U.S. patent application number 13/223210 was filed with the patent office on 2012-07-05 for systems and methods for encoding trick play streams for performing smooth visual search of media encoded for adaptive bitrate streaming via hypertext transfer protocol.
This patent application is currently assigned to Rovi Technologies Corporation. Invention is credited to Jason Braness, Kourosh Soroushian, Auke Sjoerd van der Schaar.
Application Number | 20120170642 13/223210 |
Document ID | / |
Family ID | 46380759 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120170642 |
Kind Code |
A1 |
Braness; Jason ; et
al. |
July 5, 2012 |
SYSTEMS AND METHODS FOR ENCODING TRICK PLAY STREAMS FOR PERFORMING
SMOOTH VISUAL SEARCH OF MEDIA ENCODED FOR ADAPTIVE BITRATE
STREAMING VIA HYPERTEXT TRANSFER PROTOCOL
Abstract
Systems and methods for performing smooth visual search of media
encoded for adaptive bitrate streaming using trick play streams are
disclosed. One embodiment of the invention includes transcoding a
selected portion of the source video into a portion of trick play
stream video for inclusion in a trick play stream using the source
encoder, where the portion of trick play stream video is encoded at
a lower frame rate and a lower resolution than the source video,
writing the trick play stream to a separate container file using
the source encoder, and adding an entry to an index that identifies
the location of each frame in the portion of trick play stream
video within the container file containing the trick play
stream.
Inventors: |
Braness; Jason; (San Diego,
CA) ; Soroushian; Kourosh; (San Diego, CA) ;
van der Schaar; Auke Sjoerd; (Los Angeles, CA) |
Assignee: |
Rovi Technologies
Corporation
Santa Clara
CA
|
Family ID: |
46380759 |
Appl. No.: |
13/223210 |
Filed: |
August 31, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61430110 |
Jan 5, 2011 |
|
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Current U.S.
Class: |
375/240.01 ;
375/E7.026 |
Current CPC
Class: |
H04N 21/8543 20130101;
H04N 21/44008 20130101; H04N 21/26258 20130101; H04N 21/44004
20130101; H04N 21/44209 20130101; H04N 19/40 20141101; H04N 19/593
20141101; H04L 65/607 20130101; H04N 21/2662 20130101; H04N 21/6587
20130101; H04N 21/2387 20130101; H04N 21/42607 20130101; H04N
21/23439 20130101; H04N 21/435 20130101; H04N 21/8456 20130101;
G11B 27/322 20130101; G11B 27/005 20130101; H04N 21/85406 20130101;
H04N 19/172 20141101; G11B 27/11 20130101; H04N 19/177 20141101;
H04N 21/8455 20130101; H04L 65/4084 20130101; H04N 21/234345
20130101; H04L 65/4092 20130101 |
Class at
Publication: |
375/240.01 ;
375/E07.026 |
International
Class: |
H04N 11/04 20060101
H04N011/04 |
Claims
1. A method of encoding source video as a plurality of alternative
streams and a trick play stream using a source encoder, the method
comprising: repeatedly selecting a portion of the source video
using the source encoder; transcoding the selected portion of the
source video into a plurality of alternative portions of encoded
video using the source encoder, where each alternative portion is
encoded using a different set of encoding parameters and commences
with an intra frame starting a closed group of pictures (GOP);
transcoding the selected portion of the source video into a portion
of trick play stream video for inclusion in a trick play stream
using the source encoder, where the portion of trick play stream
video is encoded at a lower frame rate and a lower resolution than
the source video; writing each of the alternative portions of
encoded video to a separate container file using the source
encoder; writing the trick play stream to a separate container file
using the source encoder; and adding an entry to an index that
identifies the location of each frame in the portion of trick play
stream video within the container file containing the trick play
stream.
2. The method of claim 1, wherein transcoding a selected portion of
the source video into a portion of trick play stream video further
comprises transcoding the selected portion so that each frame is an
IDR frame.
3. The method of claim 1, wherein the selected portions of source
video are selected based upon their duration.
4. The method of claim 3, wherein the selected portions of source
video each have a duration of two seconds.
5. The method of claim 1, wherein the container files containing
the alternative streams and the trick play stream are Extensible
Binary Markup Language (EBML) container files.
6. The method of claim 5, wherein: the element of the EBML
container file to which each alternative portion of encoded video
is written is a Cluster element; and each Cluster element to which
each of the alternative portions of encoded video is written is
assigned the same time code.
7. The method of claim 6, wherein the element of the EBML container
file to which the portion of trick play stream video is written is
a Cluster element.
8. The method of claim 7, wherein the frames of each portion of
encoded video are contained within elements within the Cluster
element.
9. The method of claim 8, wherein the first element that contains a
frame in the Cluster element contains the intra frame.
10. The method of claim 9, wherein the first element that contains
a frame is a BlockGroup element that contains a Block element,
which specifies the time code attribute of the intra frame relative
to the time code of the Cluster element.
11. The method of claim 8, wherein each frame in the portion of
trick play stream video is an intra frame.
12. The method of claim 11, wherein each element containing a frame
in the Cluster element is a BlockGroup element containing the
portion of trick play stream video contains a Block element, which
specifies the time code attribute of the intra frame relative to
the time code of the Cluster element.
13. The method of claim 12, wherein adding an entry to an index
that identifies the location of each frame in the portion of trick
play stream video within the container file containing the trick
play stream, further comprises adding the location of each
BlockGroup element in the Cluster element containing the portion of
trick play stream video to the index for the EBML container file
containing the trick play stream.
14. The method of claim 13, further comprising packing the index
for the EBML container file containing the trick play stream into
the EBML container file containing the trick play stream.
15. The method of claim 14, wherein each index comprises a Cues
element.
16. The method of claim 15, wherein: each Cues element includes a
CuePoint element that points to the location of the Cluster element
containing the portion of trick play stream video within the EBML
file containing the trick play stream; and each CuePoint element
comprises a plurality of elements that point to the BlockGroup
elements within the Cluster element pointed to by the CuePoint
element.
17. The method of claim 5, further comprising writing an element to
each of the EBML container files specifying a set of encoding
parameters.
18. The method of claim 17, wherein the set of encoding parameters
includes at least one parameter selected from the group consisting
of frame rate, frame height, frame width, sample, aspect ratio,
maximum bitrate, and minimum buffer size.
19. The method of claim 1, further comprising creating a top level
index file that identifies each of the container files containing
the alternative streams used during normal playback of the encoded
video and identifies the container file that includes the trick
play stream used during visual search of the encoded video.
20. A source encoder configured to encode source video as a
plurality of alternative streams and a trick play stream, the
source encoder comprising: a processor configured to communicate
with memory, the processor configured by a source encoder
application stored in memory; wherein the source encoder
application configures the processor to: repeatedly select a
portion of the source video using the source encoder; transcode the
selected portion of the source video into a plurality of
alternative portions of encoded video, where each alternative
portion is encoded using a different set of encoding parameters and
commences with an intra frame starting a closed group of pictures
(GOP); transcode the selected portion of the source video into a
portion of trick play stream video for inclusion in a trick play
stream using the source encoder, where the portion of trick play
stream video is encoded at a lower frame rate and a lower
resolution than the source video; write each of the alternative
portions of encoded video to a separate container file using the
source encoder; write the trick play stream to a separate container
file using the source encoder; and add an entry to an index that
identifies the location of each frame in the portion of trick play
stream video within the container file containing the trick play
stream.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/430,110, entitled "Systems and Methods for
Adaptive Bitrate Streaming of Media Stored in Matroska Files Using
Hypertext Transfer Protocol", filed Jan. 5, 2011. The disclosure of
U.S. Provisional Application Ser. Nos. 61/430,110 is herein
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to adaptive
streaming and more specifically to adaptive bitrate streaming
systems that include visual search functionality.
BACKGROUND
[0003] The term streaming media describes the playback of media on
a playback device, where the media is stored on a server and
continuously sent to the playback device over a network during
playback. Typically, the playback device stores a sufficient
quantity of media in a buffer at any given time during playback to
prevent disruption of playback due to the playback device
completing playback of all the buffered media prior to receipt of
the next portion of media. Adaptive bit rate streaming or adaptive
streaming involves detecting the present streaming conditions (e.g.
the user's network bandwidth and CPU capacity) in real time and
adjusting the quality of the streamed media accordingly. Typically,
the source media is encoded at multiple bit rates and the playback
device or client switches between streaming the different encodings
depending on available resources.
[0004] During streaming, a user may desire to view a different
portion of the media. So called "trick play" functions are offered
by many adaptive bitrate streaming systems, which enable the user
to show intermittent frames of the video stream in the forward
direction or the reverse direction (often with audio muted). The
result is a jerky sequence of still images that the user can view
to locate a desired portion of the media from which to commence
normal playback.
[0005] Adaptive streaming solutions typically utilize either
Hypertext Transfer Protocol (HTTP), published by the Internet
Engineering Task Force and the World Wide Web Consortium as RFC
2616, or Real Time Streaming Protocol (RTSP), published by the
Internet Engineering Task Force as RFC 2326, to stream media
between a server and a playback device. HTTP is a stateless
protocol that enables a playback device to request a byte range
within a file. HTTP is described as stateless, because the server
is not required to record information concerning the state of the
playback device requesting information or the byte ranges requested
by the playback device in order to respond to requests received
from the playback device. RTSP is a network control protocol used
to control streaming media servers. Playback devices issue control
commands; such as "play" and "pause", to the server streaming the
media to control the playback of media files. When RTSP is
utilized, the media server records the state of each client device
and determines the media to stream based upon the instructions
received from the client devices and the client's state.
[0006] In adaptive streaming systems, the source media is typically
stored on a media server as a top level index file pointing to a
number of alternate streams that contain the actual video and audio
data. Each stream is typically stored in one or more container
files. Different adaptive streaming solutions typically utilize
different index and media containers. The Synchronized Multimedia
Integration Language (SMIL) developed by the World Wide Web
Consortium is utilized to create indexes in several adaptive
streaming solutions including IIS Smooth Streaming developed by
Microsoft Corporation of Redmond, Wash., and Flash Dynamic
Streaming developed by Adobe Systems Incorporated of San Jose,
Calif. HTTP Adaptive Bitrate Streaming developed by Apple Computer
Incorporated of Cupertino, Calif. implements index files using an
extended M3U playlist file (.M3U8), which is a text file containing
a list of URIs that typically identify a media container file. The
most commonly used media container formats are the MP4 container
format specified in MPEG-4 Part 14 (i.e. ISO/IEC 14496-14) and the
MPEG transport stream (TS) container specified in MPEG-2 Part 1
(i.e. ISO/IEC Standard 13818-1). The MP4 container format is
utilized in IIS Smooth Streaming and Flash Dynamic Streaming. The
TS container is used in HTTP Adaptive Bitrate Streaming.
[0007] The Matroska container is a media container developed as an
open standard project by the Matroska non-profit organization of
Aussonne, France. The Matroska container is based upon Extensible
Binary Meta Language (EBML), which is a binary derivative of the
Extensible Markup Language (XML). Decoding of the Matroska
container is supported by many consumer electronics (CE) devices.
The DivX Plus file format developed by DivX, LLC of San Diego,
Calif. utilizes an extension of the Matroska container format (i.e.
is based upon the Matroska container format, but includes elements
that are not specified within the Matroska format).
SUMMARY OF THE INVENTION
[0008] Systems and methods in accordance with embodiments of the
invention perform smooth visual search of media encoded for
adaptive bitrate streaming using trick play streams. A trick play
stream encodes the source media in such a way that playback of the
trick play stream with appropriate manipulation of the timestamps
of the frames of the trick play stream appears to the user to be
source media played back at a higher speed. In this way, the trick
play stream can be utilized to perform a smooth visual search as
opposed to the disjointed sequence of frames experienced when
visual search is performed by jumping between intra or IDR frames
in one of the streams utilized for normal playback. One embodiment
of the invention includes repeatedly selecting a portion of the
source video using the source encoder, transcoding the selected
portion of the source video into a plurality of alternative
portions of encoded video using the source encoder, where each
alternative portion is encoded using a different set of encoding
parameters and commences with an intra frame starting a closed
group of pictures (GOP), transcoding the selected portion of the
source video into a portion of trick play stream video for
inclusion in a trick play stream using the source encoder, where
the portion of trick play stream video is encoded at a lower frame
rate and a lower resolution than the source video, writing each of
the alternative portions of encoded video to a separate container
file using the source encoder, writing the trick play stream to a
separate container file using the source encoder, and adding an
entry to an index that identifies the location of each frame in the
portion of trick play stream video within the container file
containing the trick play stream.
[0009] In a further embodiment of the invention, transcoding a
selected portion of the source video into a portion of trick play
stream video further comprises transcoding the selected portion so
that each frame is an IDR frame.
[0010] In another embodiment, the selected portions of source video
are selected based upon their duration.
[0011] In a still further embodiment, the selected portions of
source video each have a duration of two seconds.
[0012] In still another embodiment, the container files containing
the alternative streams and the trick play stream are Extensible
Binary Markup Language (EBML) container files.
[0013] In a yet further embodiment, the element of the EBML
container file to which each alternative portion of encoded video
is written is a Cluster element, and each Cluster element to which
each of the alternative portions of encoded video is written is
assigned the same time code.
[0014] In yet another embodiment, the element of the EBML container
file to which the portion of trick play stream video is written is
a Cluster element.
[0015] In a further embodiment again, the frames of each portion of
encoded video are contained within elements within the Cluster
element.
[0016] In another embodiment again, the first element that contains
a frame in the Cluster element contains the intra frame.
[0017] In a further additional embodiment, the first element that
contains a frame is a BlockGroup or a SimpleBlock element that
contains a Block element, which specifies the time code attribute
of the intra frame relative to the time code of the Cluster
element.
[0018] In a still yet further embodiment, each frame in the portion
of trick play stream video is an intra frame.
[0019] In still yet another embodiment, each element containing a
frame in the Cluster element is a BlockGroup or a SimpleBlock
element containing the portion of trick play stream video contains
a Block element, which specifies the time code attribute of the
intra frame relative to the time code of the Cluster element.
[0020] In a still further embodiment again, adding an entry to an
index that identifies the location of each frame in the portion of
trick play stream video within the container file containing the
trick play stream, further comprises adding the location of each
BlockGroup element in the Cluster element containing the portion of
trick play stream video to the index for the EBML container file
containing the trick play stream.
[0021] Still another embodiment again also includes packing the
index for the EBML container file containing the trick play stream
into the EBML container file containing the trick play stream.
[0022] In a still further additional embodiment, each index
comprises a Cues element.
[0023] In still another additional embodiment, each Cues element
includes a CuePoint element that points to the location of the
Cluster element containing the portion of trick play stream video
within the EBML file containing the trick play stream, and each
CuePoint element comprises a plurality of elements that point to
the BlockGroup elements within the Cluster element pointed to by
the CuePoint element.
[0024] A yet further embodiment again also includes writing an
element to each of the EBML container files specifying a set of
encoding parameters.
[0025] In yet another embodiment again, the set of encoding
parameters includes at least one parameter selected from the group
consisting of frame rate, frame height, frame width, sample, aspect
ratio, maximum bitrate, and minimum buffer size.
[0026] A yet further additional embodiment, also includes creating
a top level index file that identifies each of the container files
containing the alternative streams used during normal playback of
the encoded video and identifies the container file that includes
the trick play stream used during visual search of the encoded
video.
[0027] Another further embodiment includes a processor configured
to communicate with memory, the processor configured by a source
encoder application stored in memory. In addition, the source
encoder application configures the processor to: repeatedly select
a portion of the source video using the source encoder; transcode
the selected portion of the source video into a plurality of
alternative portions of encoded video, where each alternative
portion is encoded using a different set of encoding parameters and
commences with an intra frame starting a closed group of pictures
(GOP); transcode the selected portion of the source video into a
portion of trick play stream video for inclusion in a trick play
stream using the source encoder, where the portion of trick play
stream video is encoded at a lower frame rate and a lower
resolution than the source video; write each of the alternative
portions of encoded video to a separate container file using the
source encoder; write the trick play stream to a separate container
file using the source encoder; and add an entry to an index that
identifies the location of each frame in the portion of trick play
stream video within the container file containing the trick play
stream.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a network diagram of an adaptive bitrate streaming
system in accordance with an embodiment of the invention.
[0029] FIG. 2 conceptually illustrates a top level index file and
Matroska container files generated by the encoding of source media
in accordance with embodiments of the invention.
[0030] FIG. 3 conceptually illustrates a specialized Matroska
container file incorporating a modified Cues element in accordance
with an embodiment of the invention.
[0031] FIGS. 4a-4c conceptually illustrate the insertion of
different types of media into the Clusters element of a Matroska
container file subject to various constrains that facilitate
adaptive bitrate streaming in accordance with embodiments of the
invention.
[0032] FIG. 4d conceptually illustrates the multiplexing of
different types of media into the Clusters element of a Matroska
container file subject to various constraints that facilitate
adaptive bitrate streaming in accordance with an embodiment of the
invention.
[0033] FIG. 4e conceptually illustrates the inclusion of a trick
play stream into the Clusters element of a Matroska container file
subject to various constraints that facilitate adaptive bitrate
streaming in accordance with an embodiment of the invention.
[0034] FIG. 5 conceptually illustrates a modified Cues element of a
specialized Matroska container file, where the Cues element
includes information enabling the retrieval of Cluster elements
using HTTP byte range requests in accordance with an embodiment of
the invention.
[0035] FIG. 5a conceptually illustrates a modified Cues element of
a specialized Matroska container file in accordance with an
embodiment of the invention, where the Cues element is similar to
the Cues element shown in FIG. 5 with the exception that attributes
that are not utilized during adaptive bitrate streaming are
removed.
[0036] FIG. 5b conceptually illustrates a modified Cues element of
a specialized Matroska container file in accordance with an
embodiment of the invention, where each CueTrackPositions element
includes non-standard CueBlockPosition attributes that point to the
BlockGroup (or SimpleBlock) elements within the Cluster element
pointed to by the CueTrackPositions element.
[0037] FIG. 6 conceptually illustrates the indexing of Cluster
elements within a specialized Matroska container file utilizing
modified CuePoint elements within the container file in accordance
with embodiments of the invention.
[0038] FIG. 7 conceptually illustrates the indexing of BlockGroup
(or SimpleBlock) elements within a specialized Matroska container
file utilizing non-standard CueBlockPosition attributes within the
container file in accordance with embodiments of the invention.
[0039] FIG. 8 is a flow chart illustrating a process for encoding
source media for adaptive bitrate streaming in accordance with an
embodiment of the invention.
[0040] FIGS. 9a-9b conceptually illustrate communication between a
playback device and an HTTP server associated with switching
between streams in response to the streaming conditions experienced
by the playback device and depending upon the index information
available to the playback device prior to the decision to switch
streams in accordance with embodiments of the invention.
DETAILED DISCLOSURE OF THE INVENTION
[0041] Turning now to the drawings, systems and methods for
encoding source media for adaptive bitrate streaming and visual
search using trick play streams are illustrated. In a number of
embodiments, source media is encoded as a number of alternative
streams for adaptive bitrate streaming and an additional trick play
stream that can be utilized to perform visual search of the encoded
media. The trick play stream encodes the source media in such a way
that playback of the trick play stream appears to the user to be
source media played back at a higher speed. In this way, the trick
play stream can be utilized to perform a smooth visual search as
opposed to the disjointed sequence of frames experienced when
visual search is performed by jumping between intra or IDR frames
in one of the streams utilized for normal playback. Each stream is
stored in a Matroska (MKV) container file. In many embodiments, the
Matroska container file is a specialized Matroska container file in
that the manner in which the media in each stream is encoded and
stored within the container is constrained to improve streaming
performance. In several embodiments, the Matroska container file is
further specialized in that additional index elements (i.e.
elements that are not specified as part of the Matroska container
format) can be included within the file to facilitate the retrieval
of individual frames of video from the trick play stream during
fast visual searches. A top level index file containing an index to
the streams contained within each of the container files is also
generated to enable adaptive bitrate streaming of the encoded
media. In many embodiments, the top level index file is a
Synchronized Multimedia Integration Language (SMIL) file containing
URIs for each of the Matroska container files. In other
embodiments, any of a variety of file formats can be utilized in
the generation of the top level index file.
[0042] The performance of an adaptive bitstrate streaming system in
accordance with embodiments of the invention can be significantly
enhanced by encoding each portion of the source video at each bit
rate in such a way that the portion of video is encoded in each
stream as a single (or at least one) closed group of pictures (GOP)
starting with an Instantaneous Decoder Refresh (IDR) frame, which
is an intra frame. In a number of embodiments, the trick play
stream is further constrained such that every frame of the trick
play stream is an IDR frame. In many embodiments, the trick play
stream is also encoded at a lower bitrate, frame rate and/or
resolution. The frames of the trick play stream are stored within
Cluster elements having time codes corresponding to the Cluster
elements of the alternative streams used during normal playback. In
this way, the playback device can switch between the alternative
streams used during normal playback and the trick play stream at
the completion of the playback of a Cluster and, irrespective of
the stream from which a Cluster is obtained the first frame in the
Cluster will be an IDR frame and can be decoded without reference
to any encoded media other than the encoded media contained within
the Cluster element.
[0043] In a number of embodiments, the indexes used in the Matroska
container files containing the alternative streams used during
normal playback is a reduced index in that the index only points to
the IDRs at the start of each cluster. Retrieval of media using
HTTP during streaming of a trick play stream can be improved by
adding additional index information to the Matroska container files
used to contain the trick play stream. The manner in which a
conventional Matroska container file identifies a BlockGroup
element within a Cluster element is using a block number. In many
embodiments, the Matroska container file format is enhanced by
adding a non-standard CueBlockPosition attribute to identify the
location of a specific BlockGroup or SimpleBlock within the
Matroska container file. In several embodiments, the
CueBlockPosition attribute identifies the location of a specific
BlockGroup or SimpleBlock within a Cluster element relative to the
start of the Clusters element. By encoding the source media so that
the index to the trick play stream identifies the location of
individual frames within the trick play stream, a playback device
can request individual frames from the trick play stream based upon
the desired playback rate (typically expressed as a multiple of the
normal playback rate) without the need to stream the entire trick
play stream.
[0044] Adaptive streaming of source media encoded in the manner
outlined above can be coordinated by a playback device in
accordance with embodiments of the invention. The playback device
obtains information concerning each of the available streams from
the top level index file and selects one or more streams to utilize
in the playback of the media. The playback device can then obtain
header information from the Matroska container files containing the
one or more bitstreams or streams, and the headers provide
information concerning the decoding of the streams. The playback
device can also request index information that indexes the encoded
media stored within the relevant Matroska container files. The
index information can be stored within the Matroska container files
or separately from the Matroska container files in the top level
index or in separate index files. The index information enables the
playback device to request byte ranges corresponding to Cluster
elements within the Matroska container file containing specific
portions of encoded media via HTTP from the server. When the user
selects to perform visual search of the encoded media using the
trick play stream, the index enables the playback device to use
multiple byte range requests to select portions of the file
containing the trick play stream corresponding to individual frames
of the trick play stream. In this way, the playback device can
request only the frames from the trick play stream utilized in the
visual search of the encoded media at a desired rate. When the user
has located the desired portion of the encoded media, the playback
device can resume adaptive bitrate streaming using the alternative
streams encoded for normal playback.
[0045] The encoding of source video for use in adaptive bitrate
streaming systems that support visual search using trick play
streams and the playback of the encoded source video using HTTP
requests to achieve visual search of the encoded media in
accordance with embodiments of the invention is discussed further
below.
Adaptive Streaming System Architecture
[0046] An adaptive streaming system in accordance with an
embodiment of the invention is illustrated in FIG. 1. The adaptive
streaming system 10 includes a source encoder 12 configured to
encode source media as a number of alternative streams. In the
illustrated embodiment, the source encoder is a server. In other
embodiments, the source encoder can be any processing device
including a processor and sufficient resources to perform the
transcoding of source media (including but not limited to video,
audio, and/or subtitles). As is discussed further below, the source
encoding server 12 can generate a top level index to a plurality of
container files containing the alternative streams used during
normal playback and a separate trick play stream. Alternative
streams are streams that encode the same media content in different
ways and/or at different bitrates to enable adaptive bitrate
streaming by performing switches between the streams during normal
playback based upon the streaming conditions. The trick play stream
is used to perform smooth visual search of the encoded media in
either the forward or reverse direction at a rate that is typically
faster than the normal playback rate. In a number of embodiments,
the streams can be encoded with different resolutions and/or at
different frame rates. In many embodiments, the trick play stream
encodes the source media in such a way that playback of the trick
play stream appears to the user to be the source media smoothly
playing back at a higher speed. The encoding of media for
performing smooth visual searching is disclosed in U.S. patent
application Ser. No. 12/260,404 entitled "Application Enhancement
Tacks" to Priyadarshi et al., filed Oct. 29, 2008. The disclosure
of U.S. patent application Ser. No. 12/260,404 is incorporated by
reference herein in its entirety. In several embodiments, the trick
play stream is encoded at a lower frame rate and/or at a lower
resolution than the other streams.
[0047] The top level index file and the container files are
uploaded to an HTTP server 14. A variety of playback devices can
then use HTTP or another appropriate stateless protocol to request
portions of the top level index file and the container files via a
network 16 such as the Internet. The playback device can select
between the alternative streams during normal playback based upon
the streaming conditions and can request frames from the trick play
stream when the user desires to perform a smooth visual search of
the encoded media.
[0048] In many embodiments, the top level index file is a SMIL file
and the media is stored in Matroska container files. As is
discussed further below, the alternative streams are stored within
the Matroska container file in a way that facilitates the adaptive
bitrate streaming of the media. In many embodiments, the Matroska
container files are specialized Matroska container files that
include enhancements (i.e. elements that do not form part of the
Matroska file format specification) that facilitate the retrieval
of specific portions of media via HTTP during the adaptive bitrate
streaming of the media. In several embodiments, the Matroska
container file containing the trick play stream includes specific
enhancements to facilitate fast visual search using the trick play
stream.
[0049] In the illustrated embodiment, playback devices include
personal computers 18 and mobile phones 20. In other embodiments,
playback devices can include consumer electronics devices such as
DVD players, Blu-ray players, televisions, set top boxes, video
game consoles, tablets, and other devices that are capable of
connecting to a server via HTTP and playing back encoded media.
Although a specific architecture is shown in FIG. 1 any of a
variety of architectures can be utilized that enable playback
devices to request portions of the top level index file and the
container files in accordance with embodiments of the
invention.
File Structure
[0050] Files generated by a source encoder and/or stored on an HTTP
server for streaming to playback devices in accordance with
embodiments of the invention are illustrated in FIG. 2. The files
utilized in the adaptive bitrate streaming of the source media
include a top level index 30 and a plurality of container files 32
that each contain at least one stream. The top level index file
describes the content of each of the container files. As is
discussed further below, the top level index file can take a
variety of forms including a SMIL file and the container files can
take a variety of forms including a specialized Matroska container
file.
[0051] In many embodiments, each Matroska container file contains a
single stream. For example, the stream could be one of a number of
alternate video streams, an audio stream, one of a number of
alternate audio streams, a subtitle stream, one of a number of
alternate subtitle streams, a trick play stream, or one of a number
of alternate trick play streams. In several embodiments, the
Matroska container file includes multiple multiplexed streams. For
example, the Matroska container could include a video stream, and
one or more audio streams, one or more subtitle streams, and/or one
or more trick play streams. As is discussed further below, in many
embodiments the Matroska container files are specialized files. The
encoding of the media and the manner in which the media is stored
within Cluster elements within the Matroska container file can be
subject to constraints designed to enhance the performance of an
adaptive bitrate streaming system. In addition, the Matroska
container file can include index elements that facilitate the
location and downloading of Cluster elements from the various
Matroska container files during the adaptive streaming of the media
and the downloading of individual BlockGroup or SimpleBlock
elements from within a Cluster element. Top level index files and
Matroska container files that can be used in adaptive bitrate
streaming systems in accordance with embodiments of the invention
are discussed below.
Top Level Index Files
[0052] Playback devices in accordance with many embodiments of the
invention utilize a top level index file to identify the container
files that contain the streams available to the playback device for
use in adaptive bitrate streaming. In many embodiments, the top
level index files can include references to container files that
each include an alternative stream of encoded media or a trick play
stream. The playback device can utilize the information in the top
level index file to retrieve encoded media from each of the
container files according to the streaming conditions experienced
by the playback device and/or instructions from the user related to
performing visual search of the encoded media.
[0053] In several embodiments, the top level index file provides
information enabling the playback device to retrieve information
concerning the encoding of the media in each of the container files
and an index to encoded media within each of the container files.
In a number of embodiments, each container file includes
information concerning the encoded media contained within the
container file and an index to the encoded media within the
container file and the top level index file indicates the portions
of each container file containing this information. Therefore, a
playback device can retrieve the top level index file and use the
top level index file to request the portions of one or more of the
container files that include information concerning the encoded
media contained within the container file and an index to the
encoded media within the container file. A variety of top level
index files that can be utilized in adaptive bitrate streaming
systems in accordance with embodiments of the invention are
discussed further below.
Top Level Index SMIL Files
[0054] In a number of embodiments, the top level index file
utilized in the adaptive bitrate streaming of media is a SMIL file,
which is an XML file that includes a list of URIs describing each
of the streams and the container files that contain the streams.
The URI can include information such as the "system-bitrate" of the
stream contained within the stream and information concerning the
location of specific pieces of data within the container file.
[0055] The basic structure of a SMIL file involves providing an XML
declaration and a SMIL element. The SMIL element defines the
streams available for use in adaptive bitrate streaming and
includes a HEAD element, which is typically left empty and a BODY
element that typically only contains a PAR (parallel) element. The
PAR element describes streams that can be played simultaneously
(i.e. include media that can be presented at the same time).
[0056] The SMIL specification defines a number of child elements to
the PAR element that can be utilized to specify the streams
available for use in adaptive bitrate streaming. The VIDEO, AUDIO
and TEXTSTREAM elements can be utilized to define a specific video,
audio or subtitle stream. The VIDEO, AUDIO and TEXTSTREAM elements
can collectively be referred to as media objects. The basic
attributes of a media object are the SRC attribute, which specifies
the full path or a URI to a container file containing the relevant
stream, and the XML:LANG attribute, which includes a 3 letter
language code. Additional information concerning a media object can
be specified using the PARAM element. The PARAM element is a
standard way within the SMIL format for providing a general name
value pair. In a number of embodiments of the invention, specific
PARAM elements are defined that are utilized during adaptive
bitrate streaming.
[0057] In many embodiments, a "header-request" PARAM element is
defined that specifies the size of the header section of the
container file containing the stream. The value of the
"header-request" PARAM element typically specifies the number of
bytes between the start of the file and the start of the encoded
media within the file. In many embodiments, the header contains
information concerning the manner in which the media is encoded and
a playback device retrieves the header prior to playback of the
encoded media in order to be able to configure the decoder for
playback of the encoded media. An example of a "header-request"
PARAM element is follows:
TABLE-US-00001 <param name="header-request" value="1026"
valuetype="data" />
[0058] In a number of embodiments, a "mime" PARAM element is
defined that specifies the MIME type of the stream. A "mime" PARAM
element that identifies the stream as being an H.264 stream (i.e. a
stream encoded in accordance with the MPEG-4 Advanced Video Codec
standard) is as follows:
TABLE-US-00002 <param name="mime" value="V_MPEG4/ISO/AVC"
valuetype="data" />
[0059] The MIME type of the stream can be specified using a "mime"
PARAM element as appropriate to the encoding of a specific stream
(e.g. AAC audio or UTF-8 text stream).
[0060] When the media object is a VIDEO element, additional
attributes are defined within the SMIL file format specification
including the systemBitrate attribute, which specifies the bitrate
of the stream in the container file identified by the VIDEO
element, and width and height attributes, which specify the
dimensions of the encoded video in pixels. Additional attributes
can also be defined using the PARAM element. In several
embodiments, a "vbv" PARAM element is defined that specified the
VBV buffer size of the video stream in bytes. The video buffering
verifier (VBV) is a theoretical MPEG video buffer model used to
ensure that an encoded video stream can be correctly buffered and
played back at the decoder device. An example of a "vbv" PARAM
element that specifies a VBV size of 1000 bytes is as follows:
TABLE-US-00003 <param name="vbv" value="1000" valuetype="data"
/>
[0061] An example of VIDEO element including the attributes
discussed above is as follows:
TABLE-US-00004 <video src="http://cnd.com/video1_620kbps.mkv"
systemBitrate="620" width="480" height="270" > <param
name="vbv" value="1000" valuetype="data" /> </video>
[0062] Adaptive bitrate streaming systems in accordance with
embodiments of the invention can support trick play streams, which
can be used to provide smooth visual search through source content
encoded for adaptive bitrate streaming. A trick play stream can be
encoded that appears to be an accelerated visual search through the
source media when played back, when in reality the trick play
stream is simply a separate track encoding the source media at a
lower frame rate. In many embodiments of the system a VIDEO element
that references a trick play stream is indicated by the
systemProfile attribute of the VIDEO element. In other embodiments,
any of a variety of techniques can be utilized to signify within
the top level index file that a specific stream is a trick play
stream. An example of a trick play stream VIDEO element in
accordance with an embodiment of the invention is as follows:
TABLE-US-00005 <video
src="http://cnd.com/video_test2_600kbps.mkv"
systemProfile="DivXPlusTrickTrack" width="480" height="240">
<param name="vbv" value="1000" valuetype="data" /> <param
name="header-request" value="1000" valuetype="data" />
</video>
[0063] In a number of embodiments of the invention, a
"reservedBandwidth" PARAM element can be defined for an AUDIO
element. The "reservedBandwidth" PARAM element specifies the
bitrate of the audio stream in Kbps. An example of an AUDIO element
specified in accordance with an embodiment of the invention is as
follows:
TABLE-US-00006 <audio
src="http://cnd.com/audio_test1_277kbps.mkv" xml:lang="gem"
<param name="reservedBandwidth" value="128" valuetype="data"
/> />
[0064] In several embodiments, the "reservedBandwidth" PARAM
element is also defined for a TEXTSTREAM element. An example of a
TEXTSTREAM element including a "reservedBandwidth" PARAM element in
accordance with an embodiment of the invention is as follows:
TABLE-US-00007 <textstream
src="http://cnd.com/text_stream_ger.mkv" xml:lang="gem" <param
name="reservedBandwidth" value="32" valuetype="data" />
/>
[0065] In other embodiments, any of a variety of mechanisms can be
utilized to specify information concerning VIDEO, AUDIO, and
SUBTITLE elements as appropriate to specific applications.
[0066] A SWITCH element is a mechanism defined within the SMIL file
format specification that can be utilized to define adaptive or
alternative streams. An example of the manner in which a SWITCH
element can be utilized to specify alternative video streams at
different bitrates is as follows:
TABLE-US-00008 <switch> <video
src="http://cnd.com/video_test1_300kbps.mkv"/> <video
src="http://cnd.com/video_test2_900kbps.mkv"/> <video
src="http://cnd.com/video_test3_1200kbps.mkv"/>
</switch>
[0067] The SWITCH element specifies the URLs of three alternative
video streams. The file names indicate that the different bitrates
of each of the streams. As is discussed further below, the SMIL
file format specification provides mechanisms that can be utilized
in accordance with embodiments of the invention to specify within
the top level index SMIL file additional information concerning a
stream and the container file in which it is contained.
[0068] In many embodiments of the invention, the EXCL (exclusive)
element is used to define alternative tracks that do not adapt
during playback with streaming conditions. For example, the EXCL
element can be used to define alternative audio tracks or
alternative subtitle tracks. An example of the manner in which an
EXCL element can be utilized to specify alternative English and
French audio streams is as follows:
TABLE-US-00009 <excl> <audio
src="http://cnd.com/english-audio.mkv" xml:lang="eng"/>
<audio src="http://cnd.com/french-audio.mkv" xml:lang="fre"/>
</excl>
[0069] An example of a top level index SMIL file that defines the
attributes and parameters of two alternative video levels, an audio
stream and a subtitle stream in accordance with an embodiment of
the invention is as follows:
TABLE-US-00010 <?xml version="1.0" encoding="utf-8"?>
<smil xmlns="http://www.w3.org/ns/SMIL" version="3.0"
baseProfile="Language"> <head> </head> <body>
<par> <switch> <video
src="http://cnd.com/video_test1_300kbps.mkv" systemBitrate="300"
vbv="600" width="320" height="240" > <param name="vbv"
value="600" valuetype="data" /> <param name="header-request"
value="1000" valuetype="data" /> </video> <video
src="http://cnd.com/video_test2_600kbps.mkv" systemBitrate="600"
vbv ="900" width="640" height="480"> <param name="vbv"
value="1000" valuetype="data" /> <param name="header-request"
value="1000" valuetype="data" /> </video> </switch>
<audio src="http://cnd.com/audio.mkv" xml:lang="eng">
<param name="header-request" value="1000" valuetype="data" />
<param name="reservedBandwidth" value="128" valuetype="data"
/> </audio> <textstream
src="http://cnd.com/subtitles.mkv" xml:lang="eng"> <param
name="header-request" value="1000" valuetype="data" /> <param
name="reservedBandwidth" value="32" valuetype="data" />
</textstream> </par> </body> </smil>
[0070] The top level index SMIL file can be generated when the
source media is encoded for playback via adaptive bitrate
streaming. Alternatively, the top level index SMIL file can be
generated when a playback device requests the commencement of
playback of the encoded media. When the playback device receives
the top level index SMIL file, the playback device can parse the
SMIL file to identify the available streams. The playback device
can then select the streams to utilize to playback the content and
can use the SMIL file to identify the portions of the container
file to download to obtain information concerning the encoding of a
specific stream and/or to obtain an index to the encoded media
within the container file.
[0071] Although top level index SMIL files are described above, any
of a variety of top level index file formats can be utilized to
create top level index files as appropriate to a specific
application in accordance with an embodiment of the invention. The
use of top level index files to enable playback of encoded media
using adaptive bitrate streaming in accordance with embodiments of
the invention is discussed further below.
Storing Media in Matroska Files for Streaming
[0072] A Matroska container file used to store encoded video in
accordance with an embodiment of the invention is illustrated in
FIG. 3. The container file 32 is an Extensible Binary Markup
Language (EBML) file that is an extension of the Matroska container
file format. The specialized Matroska container file 32 includes a
standard EBML element 34, and a standard Segment element 36 that
includes a standard Seek Head element 40, a standard Segment
Information element 42, and a standard Tracks element 44. These
standard elements describe the media contained within the Matroska
container file. The Segment element 36 also includes a standard
Clusters element 46. As is described below, the manner in which
encoded media is inserted within individual Cluster elements 48
within the Clusters element 46 is constrained to improve the
playback of the media in an adaptive streaming system. In many
embodiments, the constraints imposed upon the encoded video are
consistent with the specification of the Matroska container file
format and involve encoding the video so that each Cluster includes
at least one closed GOP commencing with an IDR frame. When the
stream is a trick play stream, each frame in the stream is an IDR
frame. In addition to the above standard elements, the Segment
element 36 also includes a modified version of the standard Cues
element 52. As is discussed further below, the Cues element
includes specialized CuePoint elements (i.e. non-standard CuePoint
elements) that facilitate the retrieval of the media contained
within specific Cluster elements via HTTP and, in the case of the
trick play stream, facilitate the retrieval of specific frames of
video from within specific Cluster elements via HTTP or a similar
stateless protocol.
[0073] The constraints imposed upon the encoding of media and the
formatting of the encoded media within the Clusters element of a
Matroska container file for adaptive bitrate streaming supporting
visual search and the additional index information inserted within
the container file based upon whether the stream is one of the
alternative streams used during normal playback or a trick play
stream in accordance with embodiments of the invention is discussed
further below.
Encoding Media for Insertion in Cluster Elements
[0074] An adaptive bitrate streaming system provides a playback
device with the option of selecting between different streams of
encoded media during playback according to the streaming conditions
experienced by the playback device or in response to a user
instruction to perform a visual search using the trick play stream.
In many embodiments, switching between streams is facilitated by
separately pre-encoding discrete portions of the source media in
accordance with the encoding parameters of each stream and then
including each separately encoded portion in its own Cluster
element within the stream's container file. Furthermore, the media
contained within each cluster is encoded so that the media is
capable of playback without reference to media contained in any
other cluster within the stream. In this way, each stream includes
a Cluster element corresponding to the same discrete portion of the
source media and, at any time, the playback device can select the
Cluster element from the stream that is most appropriate to the
streaming conditions experienced by the playback device and can
commence playback of the media contained within the Cluster
element. Accordingly, the playback device can select clusters from
different streams as the streaming conditions experienced by the
playback device change over time. When the user provides a trick
play command, the playback device can select frames from an
appropriate Cluster element in the trick play stream based upon the
direction of visual search and the speed of the visual search. The
frame rate of the trick play stream is typically much lower than
that of the other streams (e.g. 5 frames per second of the source
content as opposed to 30 frames per second of the source content
for a stream used during normal playback). In many embodiments,
each frame of the trick play stream is an IDR frame. By playing
back the frames of the trick play stream at a higher speed than the
nominal frame rate of the trick play stream, a smooth visual search
can be provided without significantly increasing the processing
burden on the decode device beyond that typically experienced
during normal playback. The specific constraints applied to the
media encoded within each Cluster element depending upon the type
of media (i.e. video, audio, or subtitles) are discussed below.
[0075] A Clusters element of a Matroska container file containing a
video stream in accordance with an embodiment of the invention is
illustrated in FIG. 4a. The Clusters element 46 includes a
plurality of Cluster elements 48 that each contain a discrete
portion of encoded video. In the illustrated embodiment, each
Cluster element 48 includes encoded video corresponding to a two
second fragment of the source video. In other embodiments, the
Cluster elements include encoded video corresponding to a portion
of the source video having a greater or lesser duration than two
seconds. The smaller the Cluster elements (i.e. the smaller the
duration of the encoded media within each Cluster element), the
higher the overhead associated with requesting each Cluster
element. Therefore, a tradeoff exists between the responsiveness of
the playback device to changes in streaming conditions and the
effective data rate of the adaptive streaming system for a given
set of streaming conditions (i.e. the portion of the available
bandwidth actually utilized to transmit encoded media). In a number
of embodiments, the Cluster elements of the alternative video
streams used during normal playback contain portions of video
having the same duration and the Cluster elements of the trick play
stream have a longer duration. In a number of embodiments, the
Cluster elements of the alternative video streams contain two
second portions of video and the Cluster elements containing the
trick play stream contain 64 frames of video, which corresponds to
approximately 12.8 seconds of the source media (depending on the
frame rate of the trick play stream). In several embodiments, the
encoded video sequences in the Cluster elements for a stream have
different durations. Each Cluster element 48 includes a Timecode
element 60 indicating the start time of the encoded video within
the Cluster element and a plurality of BlockGroup (or SimpleBlock)
elements. As noted above, the encoded video stored within the
Cluster is constrained so that the encoded video can be played back
without reference to the encoded, video contained within any of the
other Cluster elements in the container file. In many embodiments,
encoding the video contained within the Cluster element as a GOP in
which the first frame is an IDR frame enforces the constraint. In
the illustrated embodiment, the first BlockGroup (or SimpleBlock)
element 62 contains an IDR frame (i.e. an intra frame). Therefore,
the first BlockGroup (or SimpleBlock) element 62 does not include a
ReferenceBlock element. The first BlockGroup (or SimpleBlock)
element 62 includes a Block element 64, which specifies the
Timecode attribute of the frame encoded within the Block element 64
relative to the Timecode of the Cluster element 48. Subsequent
BlockGroup (or SimpleBlock) elements 66 are not restricted in the
types of frames that they can contain (other than that they cannot
reference frames that are not contained within the Cluster
element). Therefore, subsequent BlockGroup (or SimpleBlock)
elements 66 can include ReferenceBlock elements 68 referencing
other BlockGroup element(s) utilized in the decoding of the frame
contained within the BlockGroup (or SimpleBlock) element or can
contain IDR frames and are similar to the first BlockGroup (or
SimpleBlock) element 62. As noted above, the manner in which
encoded video is inserted within the Cluster elements of the
Matroska file conforms with the specification of the Matroska file
format.
[0076] The insertion of encoded audio and subtitle information
within a Clusters element 46 of a Matroska container file in
accordance with embodiments of the invention is illustrated in
FIGS. 4b and 4c. In the illustrated embodiments, the encoded media
is inserted within the Cluster elements 48 subject to the same
constraints applied to the encoded video discussed above with
respect to FIG. 4a. In addition, the duration of the encoded audio
and subtitle information within each Cluster element corresponds to
the duration of the encoded video in the corresponding Cluster
element of the Matroska container file containing the encoded
video. In other embodiments, the Cluster elements within the
container files containing the audio and/or subtitle streams need
not correspond with the start time and duration of the Cluster
elements in the container files containing the alternative video
streams.
Multiplexing Streams in a Single MKV Container File
[0077] The Clusters elements shown in FIGS. 4a-4c assume that a
single stream is contained within each Matroska container file. In
several embodiments, media from multiple streams is multiplexed
within a single Matroska container file. In this way, a single
container file can contain a video stream multiplexed with one or
more corresponding audio streams, and/or one or more corresponding
subtitle streams. Storing the streams in this way can result in
duplication of the audio and subtitle streams across multiple
alternative video streams. However, the seek time to retrieve
encoded media from a video stream and an associated audio, and/or
subtitle stream can be reduced due to the adjacent storage of the
data on the server. The Clusters element 46 of a Matroska container
file containing multiplexed video, audio and subtitle data in
accordance with an embodiment of the invention is illustrated in
FIG. 4d. In the illustrated embodiment, each Cluster element 48
includes additional BlockGroup (or SimpleBlock) elements for each
of the multiplexed streams. The first Cluster element includes a
first BlockGroup (or SimpleBlock) element 62v for encoded video
that includes a Block element 64v containing an encoded video frame
and indicating the Timecode attribute of the frame relative to the
start time of the Cluster element (i.e. the Timecode attribute 60).
A second BlockGroup (or SimpleBlock) element 62a includes a Block
element 64a including an encoded audio sequence and indicating the
timecode of the encoded audio relative to the start time of the
Cluster element, and a third BlockGroup (or SimpleBlock) element
62s including a Block element 64s containing an encoded subtitle
and indicating the timecode of the encoded subtitle relative to the
start time of the Cluster element. Although not shown in the
illustrated embodiment, each Cluster element 48 likely would
include additional BlockGroup (or SimpleBlock) elements containing
additional encoded video, audio or subtitles. Despite the
multiplexing of the encoded video, audio, and/or subtitle streams,
the same constraints concerning the encoded media apply.
Incorporating Trick Play Streams in MKV Container Files
[0078] As noted above, a separate trick play stream can be encoded
that appears to be a smooth visual search through the source media
when played back, when in reality the trick play stream is simply a
separate stream encoding the source media at a lower frame rate and
played back at a higher rate. In several embodiments, the trick
play stream is created by generating a trick play stream in the
manner outlined in U.S. patent application Ser. No. 12/260,404 and
inserting the trick play stream into a Matroska container file
subject to the constraints mentioned above with respect to
insertion of a video stream into a Matroksa container file. In many
embodiments, the trick play stream is also subject to the further
constraint that every frame in each Cluster element in the trick
play stream is encoded as an IDR frame (i.e. an intra frame).
Transitions to and from a trick play stream can be treated in the
same way as transitions between any of the other encoded streams
are treated within an adaptive bitrate streaming system in
accordance with embodiments of the invention. As noted above,
however, the duration of the Cluster elements of the trick play
streams need not correspond to the duration of the Cluster elements
of the alternative video streams utilized during normal playback.
Playback of the frames contained within the trick play stream to
achieve accelerated visual search typically involves the playback
device manipulating the timecodes assigned to the frames of encoded
video prior to providing the frames to the playback device's
decoder to achieve a desired increase in rate of accelerated search
(e.g. x2, x4, x6, etc.).
[0079] A Clusters element containing encoded media from a trick
play stream is shown in FIG. 4e. In the illustrated embodiment, the
encoded trick play stream is inserted within the Cluster elements
48 subject to the same constraints applied to the encoded video
discussed above with respect to FIG. 4a. However, each Block
element contains an IDR. Therefore, the BlockGroup (or SimpleBlock)
elements do not include a ReferenceBlock element. In other
embodiments, the Cluster elements within the container file
containing the trick play stream need not correspond with the start
time and duration of the Cluster elements in the container files
containing the alternative video streams utilized during normal
playback. Furthermore, the frames of the trick play stream can be
contained within a SimpleBlock element.
[0080] In many embodiments, source content can be encoded to
provide a single trick play stream or multiple trick play streams
for use by the adaptive bit rate streaming system. When a single
trick play stream is provided, the trick play stream is typically
encoded at a low bitrate, low frame rate and low resolution. For
example, a trick play stream could be encoded at around 384 kbps
with a frame rate of 5 fps. In a number of instances, a trick play
stream could also be encoded at a lower resolution. Even when the
trick play stream is encoded at a very low bitrate requesting all
frames of the trick play stream can require considerable bandwidth.
For example, a trick play stream encoded at 384 kbps and 5 fps
played at 8.times. visual search speed utilizes at least 2,304
kbps, which is much higher than the lowest streaming levels that
are used in many adaptive bitrate streaming systems, and is played
back at 40 fps, which is beyond the capabilities of most devices
(typically limited to 30 fps). Therefore, the visual search could
stall at high visual search speeds during network congestion or
simply due to the limitations of the playback device. In a number
of embodiments of the invention, the bandwidth utilized during
visual search is reduced by only requesting the frames from the
trick play stream utilized at the visual search speed. In this way,
the frame rate and the bandwidth utilization can remain relatively
constant irrespective of the speed of the visual search. As is
discussed further below, the ability to request individual frames
from within a Cluster element involves utilizing a modified Cues
element to index the content within a Matroska container file
containing a trick play stream to index each frame within the trick
play stream.
[0081] When multiple alternative trick play streams are provided, a
separate trick play stream can be utilized for each visual search
speed. Multiple alternative trick play streams can also be provided
that encode the trick play stream at different bitrates to enable
adaptive rate streaming with respect to the trick play stream.
Indexing Clusters within MKV Container Files for Normal
Playback
[0082] The specification for the Matroska container file format
provides for an optional Cues element that is used to index Block
elements within the container file. A modified Cues element 52 that
can be incorporated into a Matroska container file in accordance
with an embodiment of the invention to facilitate the requesting of
clusters by a playback device using HTTP during normal playback is
illustrated in FIG. 5. The modified Cues element 52 includes a
plurality of CuePoint elements 70 that each include a CueTime
attribute 72. Each CuePoint element includes a CueTrackPositions
element 74 containing the CueTrack 76 and CueClusterPosition 78
attributes. In many embodiments, the CuePoint element is mainly
configured to identify a specific Cluster element as opposed to a
specific Block element within a Cluster element. Although, in
several applications the ability to seek to specific BlockGroup (or
SimpleBlock) elements within a Cluster element is required and
additional index information is included in the Cues element.
[0083] The use of a modified Cues element to index encoded media
within a Clusters element of a Matroska file in accordance with an
embodiment of the invention is illustrated in FIG. 6. A CuePoint
element is generated to correspond to each Cluster element within
the Matroska container file. The CueTime attribute 72 of the
CuePoint element 70 corresponds to the Timecode attribute 60 of the
corresponding Cluster element 48. In addition, the CuePoint element
contains a CueTrackPositions element 74 having a CueClusterPosition
attribute 78 that points to the start of the corresponding Cluster
element 48. The CueTrackPositions element 74 can also include a
CueBlockNumber attribute, which is typically used to indicate the
Block element containing the first IDR frame within the Cluster
element 48.
[0084] As can readily be appreciated the modified Cues element 52
forms an index to each of the Cluster elements 48 within the
Matroska container file. Furthermore, the CueTrackPosition elements
provide information that can be used by a playback device to
request the byte range of a specific Cluster element 48 via HTTP or
another suitable protocol from a remote server. The Cues element of
a conventional Matroska file does not directly provide a playback
device with information concerning the number of bytes to request
from the start of the Cluster element in order to obtain all of the
encoded video contained within the Cluster element. The size of a
Cluster element can be inferred in a modified Cuse element by using
the CueClusterPosition attribute of the CueTrackPositions element
that indexes the first byte of the next Cluster element.
Alternatively, additional CueTrackPosition elements can be added to
the modified Cues elements in accordance with embodiments of the
invention that index the last byte of the Cluster element (in
addition to the CueTrackPositions elements that index the first
byte of the Cluster element), and/or a non-standard CueClusterSize
attribute that specifies the size of the Cluster element pointed to
by the CueClusterPosition attribute is included in each
CueTrackPosition element to assist with the retrieval of specific
Cluster elements within a Matroska container file via HTTP byte
range requests or a similar protocol.
[0085] The modification of the Cues element in the manner outlined
above significantly simplifies the retrieval of Cluster elements
from a Matroska container file via HTTP or a similar protocol
during adaptive bitrate streaming. In addition, by only indexing
the first frame in each Cluster the size of the index is
significantly reduced. Given that the index is typically downloaded
prior to playback, the reduced size of the Cues element (i.e.
index) means that playback can commence more rapidly. Using the
CueClusterPosition elements, a playback device can request a
specific Cluster element from the stream most suited to the
streaming conditions experienced by the playback device by simply
referencing the index of the relevant Matroska container file using
the Timecode attribute for the desired Cluster element.
[0086] A number of the attributes within the Cues element are not
utilized during adaptive bitrate streaming. Therefore, the Cues
element can be further modified by removing the unutilized
attributes to reduce the overall size of the index for each
Matroska container file. A modified Cues element that can be
utilized in a Matroska container file that includes a single
encoded stream in accordance with an embodiment of the invention is
illustrated in FIG. 5a. The Cues element 52' shown in FIG. 5a is
similar to the Cues element 52 shown in FIG. 5 with the exception
that the CuePoint elements 70' do not include a CueTime attribute
(see 72 in FIG. 5) and/or the CueTrackPositions elements 74' do not
include a CueTrack attribute (76 in FIG. 5). When the portions of
encoded media in each Cluster element in the Motroska container
file have the same duration, the CueTime attribute is not
necessary. When the Matroska contain file includes a single encoded
stream, the CueTrack attribute is not necessary. In other
embodiments, the Cues element and/or other elements of the Matroska
container file can be modified to remove elements and/or attributes
that are not necessary for the adaptive bitrate streaming of the
encoded stream contained within the Matroska container file, given
the manner in which the stream is encoded and inserted in the
Matroska container file.
[0087] Although various modifications to the Cues element to
include information concerning the size of each of the Cluster
elements within a Matroska container file and to eliminate
unnecessary attributes are described above, many embodiments of the
invention utilize a conventional Matroska container. In several
embodiments, the playback device simply determines the size of
Cluster elements on the fly using information obtained from a
conventional Cues element, and/or relies upon a separate index file
containing information concerning the size and/or location of the
Cluster elements within the MKV container file. In several
embodiments, the additional index information is stored in the top
level index file. In a number of embodiments, the additional index
information is stored in separate files that are identified in the
top level index file. When index information utilized to retrieve
Cluster elements from a Matroska container file is stored
separately from the container file, the Matroska container file is
still typically constrained to encode media for inclusion in the
Cluster elements in the manner outlined above. In addition,
wherever the index information is located, the index information
will typically index each Cluster element and include (but not be
limited to) information concerning at least the starting location
and, in many instances, the size of each Cluster element.
Indexing Clusters within a MKV Container Containing a Trick Play
Stream
[0088] The modified Cues element utilized in MKV container files
containing streams utilized during normal playback index each
Cluster element within the MKV container file. As noted above, not
indexing every frame of the stream reduces the overall size of the
index and the time taken to download the index prior to the
commencement of playback. When performing higher rate visual
searches, the ability to download only the frames displayed during
the visual search can significantly reduce the bandwidth
requirements for performing visual search and the processing load
on the playback device. Therefore, the index to a container file
containing a trick play stream in accordance with many embodiments
of the invention indexes all of the frames in the trick play
stream.
[0089] A modified Cues element of a MKV container file containing a
trick play stream in accordance with an embodiment of the invention
is illustrated in FIG. 5b. The modified Cues element 52'' includes
a number of CuePoint elements 70'' that each include a CueTime
attribute 72'' and a CueTrackPositions element 74'' that references
a Cluster element within the MKV container file (now shown). Each
CueTrackPositions element 74'' includes a CueClusterPosition
attribute 78'' that indicates the location within the MKV container
file of the start of the Cluster element (now shown) referenced by
the CuePoint element 70''. The CueTrackPositions element 74'' also
includes a CueBlockPositions element 79'', which is a non-standard
element that includes CueBlockPosition attributes 80'' that
reference the starting location of each of the BlockGroup or
SimpleBlock elements that contain frames in the Cluster element
referenced by the CuePoint element 70''. The MKV container file
format specification does not provide for the indexing of the
location of BlockGroups (or SimpleBlocks) within the MKV container
file. Therefore, the CueBlockPostion element 79'' is a non-standard
element specified for the purpose of supporting the selective
downloading of frames from trick play streams by playback
devices.
[0090] The manner in which CueBlockPosition attributes of a
modified Cues element in an MKV container file containing a trick
play stream reference the BlockGroup or SimpleBlock elements in the
Cluster elements of the MKV container file in accordance with an
embodiment of the invention is illustrated in FIG. 7. The
CueClusterPosition attribute 78'' in each CueTrackPositions element
74'' points to the start of a Cluster element 48 within the MKV
container file. The CueBlockPosition attributes 80'' within the
CueBlockPositions element 79'' point to the start of each
BlockGroup or SimpleBlock element 62 within the Cluster element
pointed to by the CueCluster Position attribute 78''. In many
embodiments, the CueBlockPositions element 79'' is identified with
the ID 0x78 and the CueBlockPosition attribute 80'' is identified
with the ID 0x79. In this way, a playback device can use multiple
byte range HTTP requests to only request the portions of each
Cluster (i.e. the BlockGroup or Simple Block elements) containing
the frames that will be utilized during visual search. When a
playback device selectively requests portions of the Cluster
element to exclude specific BlockGroup or SimpleBlock elements, the
Cluster element that is received by the playback device is a valid
Cluster element with the exception that the size attribute of the
Cluster element will be incorrect. In a number of embodiments, the
size of the Cluster element is modified by the playback device as
it is received and/or parsed so that it can be processed like any
other Cluster element. Playback of trick play streams in accordance
with embodiments of the invention is discussed further below.
Encoding Source Media for Adaptive Bitrate Streaming
[0091] A process for encoding source media as a top level index
file and a plurality of Matroska container files for use in an
adaptive bitrate streaming system in accordance with an embodiment
of the invention is illustrated in FIG. 8. The encoding process 100
commences by selecting (102) a first portion of the source media
and encoding (104) the source media using the encoding parameters
for each stream. When the portion of media is video, then the
portion of source video is encoded as a single GOP commencing with
an IDR frame. In many embodiments, encoding parameters used to
create the alternative GOPs vary based upon bitrate, frame rate,
encoding parameters and resolution. In this way, the portion of
media is encoded as a set of interchangeable alternatives and a
portion of a trick play stream. A playback device can select the
alternative most appropriate to the streaming conditions
experienced by the playback device and can utilize the trick play
stream to perform visual search of the encoded media. When
different resolutions are supported, the encoding of the streams is
constrained so that each stream has the same display aspect ratio.
A constant display aspect ratio can be achieved across different
resolution streams by varying the sample aspect ratio with the
resolution of the stream. In many instances, reducing resolution
can result in higher quality video compared with higher resolution
video encoded at the same bit rate. In many embodiments, the source
media is itself encoded and the encoding process (104) involves
transcoding or transrating of the encoded source media according to
the encoding parameters of each of the alternative streams
supported by the adaptive bitrate streaming system.
[0092] Once the source media has been encoded as a set of
alternative portions of encoded media, each of the alternative
portions of encoded media is inserted (106) into a Cluster element
within the Matroska container file corresponding to the stream to
which the portion of encoded media belongs. In many embodiments,
the encoding process also constructs indexes for each Matroska
container file as media is inserted into Cluster elements within
the container. Therefore, the process 100 can also include creating
a CuePoint element that points to the Cluster element inserted
within the Matroska container file. When the CuePoint element
points to the Cluster element of a trick play stream, the CuePoint
element also includes CueBlockPosition attributes that point to the
BlockGroup (or SimpleBlock) elements within the Cluster element.
The CuePoint element can be held in a buffer until the source media
is completely encoded. Although the above process describes
encoding each of the alternative portions of encoded media and the
portion of media included in the trick play stream sequentially in
a single pass through the source media, many embodiments of the
invention involve performing a separate pass through the source
media to encode each of the alternative streams and/or the trick
play stream.
[0093] Referring back to FIG. 8, the process continues to select
(102) and encode (104) portions of the source media and then insert
(106) the encoded portions of media into the Matroska container
file corresponding to the appropriate stream until the entire
source media is encoded for adaptive bitrate streaming (108). At
which point, the process can insert an index (110) into the
Matroska container for each stream and create (112) a top level
index file that indexes each of the encoded streams contained
within the Matroska container files. As noted above, the indexes
can be created as encoded media is inserted into the Matroska
container files so that a CuePoint element indexes each Cluster
element within the Mastroska container file (and BlockGroup or
SimpleBlock elements when the Matroska container file contains a
trick play stream). Upon completion of the encoding each of the
CuePoint elements can be included in a Cues element and the Cues
element inserted into the Matroska container file following the
Clusters element.
[0094] Following the encoding of the source media to create
Matroska container files containing each of the streams generated
during the encoding process, which can include the generation of
trick play streams, and a top level index file that indexes each of
the streams within the Matroska container files, the top level
index file and the Matroska container files can be uploaded to an
HTTP server for adaptive bitrate streaming to playback devices. The
adaptive bitrate streaming of media encoded in accordance with
embodiments of the invention using HTTP requests is discussed
further below.
Adaptive Bitrate Streaming from MKV Container Files Using Http
[0095] When source media is encoded so that there are alternative
streams contained in separate Matroska container files for at least
one of video, audio, and subtitle content, adaptive streaming of
the media contained within the Matroska container files can be
achieved using HTTP requests or a similar stateless data transfer
protocol. HTTP requests can also be used to transition from normal
playback to visual search using a separate trick play stream. In
many embodiments, a playback device requests the top level index
file resident on the server and uses the index information to
identify the streams that are available to the playback device. The
playback device can then retrieve the indexes for one or more of
the Matroska files and can use the indexes to request media from
one or more of the streams contained within the Matroska container
files using HTTP requests or using a similar stateless protocol. As
noted above, many embodiment of the invention implement the indexes
for each of the Matroska container files using a modified Cues
element. In a number of embodiments, however, the encoded media for
each stream is contained within a standard Matroska container file
and separate index file(s) can also be provided for each of the
container files. Based upon the streaming conditions experienced by
the playback device, the playback device can select media from
alternative streams encoded at different bitrates. When the media
from each of the streams is inserted into the Matroska container
file in the manner outlined above, transitions between streams can
occur upon the completion of playback of media within a Cluster
element. This is true whether the transition is between alternative
streams during normal playback or a trick play stream utilized
during visual search. Therefore, the size of the Cluster elements
(i.e the duration of the encoded media within the Cluster elements)
is typically chosen so that the playback device is able to respond
quickly enough to changing streaming conditions and to instructions
from the user that involve utilization of a trick play stream. The
smaller the Cluster elements (i.e. the smaller the duration of the
encoded media within each Cluster element) the higher the overhead
associated with requesting each Cluster element. Therefore, a
tradeoff exists between the responsiveness of the playback device
to changes in streaming conditions and the effective data rate of
the adaptive streaming system for a given set of streaming
conditions (i.e. the portion of the available bandwidth actually
utilized to transmit encoded media). In many embodiments, the size
of the Cluster elements is chosen so that each Cluster element
contains two seconds of encoded media. In other embodiments, the
duration of the encoded media can be greater or less than two
seconds and/or the duration of the encoded media can vary from
Cluster element to Cluster element.
[0096] Communication between a playback device or client and an
HTTP server during the normal playback of media encoded in separate
streams contained within Matroska container files indexed by a top
level index file in accordance with an embodiment of the invention
is illustrated in FIG. 9a. In the illustrated embodiment, the
playback device 200 commences playback by requesting the top level
index file from the server 202 using an HTTP request or a similar
protocol for retrieving data. The server 202 provides the bytes
corresponding to the request. The playback device 200 then parses
the top level index file to identify the URIs of each of the
Matroska container files containing the streams of encoded media
derived from a specific piece of source media. The playback device
can then request the byte ranges corresponding to headers of one or
more of the Matroska container files via HTTP or a similar
protocol, where the byte ranges are determined using the
information contained in the URI for the relevant Matroska
container files (see discussion above). The server returns the
following information in response to a request for the byte range
containing the headers of a Matroska container file:
TABLE-US-00011 ELEM["EBML"] ELEM["SEEKHEAD"] ELEM["SEGMENTINFO"]
ELEM["TRACKS"]
[0097] The EBML element is typically processed by the playback
device to ensure that the file version is supported. The SeekHead
element is parsed to find the location of the Matroska index
elements and the SegmentInfo element contains two key elements
utilized in playback: TimecodeScale and Duration. The TimecodeScale
specifies the timecode scale for all timecodes within the Segment
of the Matroska container file and the Duration specifies the
duration of the Segment based upon the TimecodeScale. The Tracks
element contains the information used by the playback device to
decode the encoded media contained within the Clusters element of
the Matroska file. As noted above, adaptive bitrate streaming
systems in accordance with embodiments of the invention can support
different streams encoded using different encoding parameters
including but not limited to frame rate, and resolution. Therefore,
the playback device can use the information contained within the
Matroska container file's headers to configure the decoder every
time a transition is made between encoded streams.
[0098] In many embodiments, the playback device does not retrieve
the headers for all of the Matroska container files indexed in the
top level index file. Instead, the playback device determines the
stream(s) that will be utilized to initially commence playback and
requests the headers from the corresponding Matroska container
files. Depending upon the structure of the URIs contained within
the top level index file, the playback device can either use
information from the URIs or information from the headers of the
Matroska container files to request byte ranges from the server
that contain at least a portion of the index from relevant Matroska
container files. The byte ranges can correspond to the entire
index. The server provides the relevant byte ranges containing the
index information to the playback device, and the playback device
can use the index information to request the byte ranges of Cluster
elements containing encoded media using this information. When the
Cluster elements are received, the playback device can extract
encoded media from the Block elements within the Cluster element,
and can decode and playback the media within the Block elements in
accordance with their associated Timecode attributes.
[0099] In the illustrated embodiment, the playback device 200
requests sufficient index information from the HTTP server prior to
the commencement of playback that the playback device can stream
the entirety of each of the selected streams using the index
information. In other embodiments, the playback device continuously
retrieves index information as media is played back. In several
embodiments, all of the index information for the lowest bitrate
steam is requested prior to playback so that the index information
for the lowest bitrate stream is available to the playback device
in the event that streaming conditions deteriorate rapidly during
playback.
Switching Between Streams
[0100] The communications illustrated in FIG. 9a assume that the
playback device continues to request media from the same streams
(i.e. Matroska container files) throughout playback of the media.
In reality, the streaming conditions experienced by the playback
device are likely to change during the playback of the streaming
media and the playback device can request media from alternative
streams (i.e. different Matroska container files) to provide the
best picture quality for the streaming conditions experienced by
the playback device. In addition, the playback device may switch
streams in order to perform a visual search (i.e. fast forward,
rewind) trick play function that utilizes a trick play stream.
[0101] Communication between a playback device and a server when a
playback device switches to a new stream in accordance with
embodiments of the invention are illustrated in FIG. 9a. The
communications illustrated in FIG. 9a assume that the index
information for the new stream has not been previously requested by
the playback device and that downloading of Cluster elements from
the old stream proceeds while information is obtained concerning
the Matroska container file containing the new stream. When the
playback device 200 detects a change in streaming conditions,
determines that a higher bitrate stream can be utilized at the
present streaming conditions, or receives a trick play instruction
from a user, the playback device can use the top level index file
to identify the URI for a more appropriate alternative stream to at
least one of the video, audio, or subtitle streams from which the
playback device is currently requesting encoded media. The playback
device can save the information concerning the current stream(s)
and can request the byte ranges of the headers for the Matroska
container file(s) containing the new stream(s) using the parameters
of the corresponding URIs. Caching the information in this way can
be beneficial when the playback device attempts to adapt the
bitrate of the stream downward or return to the stream following
the completion of a visual search by the user. When the playback
device experiences a reduction in available bandwidth or receives
an instruction to resume normal playback, the playback device
ideally will quickly switch between streams. Due to the reduced
bandwidth experienced by the playback device, the playback device
is unlikely to have additional bandwidth to request header and
index information when there is congestion. Ideally, the playback
device utilizes all available bandwidth to download already
requested higher rate Cluster elements and uses locally cached
index information to start requesting Cluster elements from
Matroska container file(s) containing lower bitrate stream(s).
[0102] Byte ranges for index information for the Matroska container
file(s) containing the new stream(s) can be requested from the HTTP
server 202 in a manner similar to that outlined above with respect
to FIG. 9a. In the case of trick play streams, multiple byte range
HTTP requests can be used that request only the BlockGroup or
Simple Block elements from a Cluster element that will be utilized
by the playback device during the visual search of the encoded
media. Typically, the number of BlockGroup or SimpleBlock elements
that are not requested depends, upon the rate of the visual search.
As discussed above, the incorrect size attribute of the Cluster
element downloaded via HTTP in this way can be corrected based upon
the size of the data received by the playback device prior to
passing the Cluster element to a decoder. The time stamps on the
buffered frames can also be manipulated prior to providing the
frames to the playback device's decoder to achieve accelerated
playback of the buffered frames.
[0103] Once the index of the new stream is downloaded, the playback
device can stop downloading of Cluster elements from the previous
stream and can commence requesting the byte ranges of the
appropriate Cluster elements from the Matroska container file(s)
containing the new stream(s) from the HTTP server. As noted above,
the encoding of the alternative streams so that corresponding
Cluster elements within alternative streams and the trick play
stream (i.e. Cluster elements containing the same portion of the
source media encoded in accordance with different encoding
parameters) start with the same Timecode element and an IDR frame
facilitates the smooth transition from one stream to another.
[0104] When the playback device caches the header and the entire
index for each stream that has been utilized in the playback of the
media, the process of switching back to a previously used stream
can be simplified. The playback device already has the header and
index information for the Matroska file containing the previously
utilized stream and the playback device can simply use this
information to start requesting Cluster elements from the Matroska
container file of the previously utilized stream via HTTP.
Communication between a playback device and an HTTP server when
switching back to a stream(s) for which the playback device has
cached header and index information in accordance with an
embodiment of the invention is illustrated in FIG. 9b. The process
illustrated in FIG. 9b is ideally performed when adapting bitrate
downwards, because a reduction in available resources can be
exacerbated by a need to download index information in addition to
media. The likelihood of interruption to playback is reduced by
increasing the speed with which the playback device can switch
between streams and reducing the amount of overhead data downloaded
to achieve the switch.
[0105] Although the present invention has been described in certain
specific aspects, many additional modifications and variations
would be apparent to those skilled in the art. It is therefore to
be understood that the present invention may be practiced otherwise
than specifically described, including various changes in the
implementation such as utilizing encoders and decoders that support
features beyond those specified within a particular standard with
which they comply, without departing from the scope and spirit of
the present invention. Thus, embodiments of the present invention
should be considered in all respects as illustrative and not
restrictive.
* * * * *
References