U.S. patent application number 08/826345 was filed with the patent office on 2001-08-09 for interleaved multiple multimedia stream for synchronized transmission over a computer network.
Invention is credited to CHOU, PHILIP A., KLEMETS, ANDERS EDGAR.
Application Number | 20010013068 08/826345 |
Document ID | / |
Family ID | 25246300 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010013068 |
Kind Code |
A1 |
KLEMETS, ANDERS EDGAR ; et
al. |
August 9, 2001 |
INTERLEAVED MULTIPLE MULTIMEDIA STREAM FOR SYNCHRONIZED
TRANSMISSION OVER A COMPUTER NETWORK
Abstract
The production of an interleaved multimedia stream for servers
and client computers coupled to each other by a diverse computer
network which includes local area networks (LANs) and/or wide area
networks (WANs) such as the internet. Interleaved multimedia
streams can include compressed video frames for display in a video
window, accompanying compressed audio frames and annotation frames.
In one embodiment, a producer captures separate video/audio frames
and generates an interleaved multimedia file. In another
embodiment, the interleaved file include annotation frames which
provide either pointer(s) to the event(s) of interest or include
displayable data embedded within the annotation stream. The
interleaved file is then stored in the web server for subsequent
retrieval by client computer(s) in a coordinated manner, so that
the client computer(s) is able to synchronously display the video
frames and displayable event(s) in a video window and event
window(s), respectively. In some embodiments, the interleaved file
includes packets with variable length fields, each of which are at
least one numerical unit in length.
Inventors: |
KLEMETS, ANDERS EDGAR;
(SUNNYVALE, CA) ; CHOU, PHILIP A.; (MENLO PARK,
CA) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG,WOESSNER & KLUTH, PA
P.O. BOX 2938
MINNEAPOLIS
MN
55402
|
Family ID: |
25246300 |
Appl. No.: |
08/826345 |
Filed: |
March 25, 1997 |
Current U.S.
Class: |
709/231 |
Current CPC
Class: |
H04L 65/752 20220501;
H04L 9/40 20220501; H04L 65/762 20220501; H04L 65/80 20130101; H04L
65/1101 20220501 |
Class at
Publication: |
709/231 |
International
Class: |
G06F 015/16 |
Claims
What is claimed is:
1. In a computer having a processor and memory, said computer
useful in association with a web server coupled to a client
computer via a network, a method for producing an interleaved
multimedia file from a video file and an audio file, the method
comprising the steps of: if a video frame buffer is empty, then
retrieving a first video frame from the video file, said first
video frame including a video timestamp; if an audio frame buffer
is empty, then retrieving a first audio frame from the audio file,
said first audio frame including an audio timestamp; and if the
video timestamp is less than or equal to the audio timestamp, then
writing the first video frame to a first packet of the interleaved
file; and retrieving a second video frame from the video file; else
if the audio timestamp is less than or equal to the video
timestamp, then writing the first audio frame to a second packet of
the interleaved file; and retrieving a second audio frame from the
audio file.
2. The method of claim 1 wherein said first and second packet has a
variable packet length field.
3. The method of claim 2 wherein the size of the variable packet
length field is at least one numerical unit, and said step of
writing the first video frame to the first packet includes the
steps of: if the size of the first video frame is less than one
numerical unit, then writing the size into a length field of the
variable packet length field of the first packet; if the size of
the first video frame is between one numerical unit and two
numerical units, then writing a null number into a null field of
the variable packet length field of the first packet; and writing
the size into the length field of the variable packet length field
of the first packet; and if the size of the first video frame is
greater than two numerical units, then writing three null numbers
into the null field of the variable packet length field of the
first packet; and writing the size into the length field of the
variable packet length field of the first packet.
4. The method of claim 1 further comprising the step of writing an
annotation frame from an annotation file into said interleaved
file.
5. A producer useful for generating an interleaved file configured
to provide a synchronized playback of a video file and an audio
file on a client computer, the producer comprising a capture module
configured to generate an interleaved file from video frames from
the video file and audio frames from the audio file, based on
timestamps of the video frames and the audio frames.
6. The producer of claim 5 further comprising an author module
configured to combined said interleaved file with a plurality of
annotation frames, based on the timestamps of the video frames, the
audio frames and the annotation frames.
7. The producer of claim 5 wherein said video and audio frames are
stored in packets with variable packet length fields.
8. A computer-readable medium useful in association with a computer
system having a processor and memory, the computer-readable medium
comprising computer-readable code instructions configured to cause
said computer system to execute the steps of: if a video frame
buffer is empty, then retrieving a first video frame from a video
file, said first video frame including a video timestamp; if an
audio frame buffer is empty, then retrieving a first audio frame
from an audio file, said first audio frame including an audio
timestamp; and if the video timestamp is less than or equal to the
audio timestamp, then writing the first video frame to a first
packet of an interleaved file; and retrieving a second video frame
from the video file; else if the audio timestamp is less than or
equal to the video timestamp, then writing the first audio frame to
a second packet of the interleaved file; and retrieving a second
audio frame from the audio file.
9. The computer-readable medium of claim 8 wherein said first and
second packet has a variable packet length field.
10. The computer-readable medium of claim 9 wherein the size of the
variable packet length field is at least one numerical unit, and
said step of writing the first video frame to the first packet
includes the steps of: if the size of the first video frame is less
than one numerical unit, then writing the size into a length field
of the variable packet length field of the first packet; if the
size of the first video frame is between one numerical unit and two
numerical units, then writing a null number into a null field of
the variable packet length field of the first packet; and writing
the size into the length field of the variable packet length field
of the first packet; and if the size of the first video frame is
greater than two numerical units, then writing three null numbers
into the null field of the variable packet length field of the
first packet; and writing the size into the length field of the
variable packet length field of the first packet.
11. The computer readable medium of claim 8 further comprising
computer-readable code instructions configured to cause said
computer system to execute the step of writing an annotation frame
from an annotation file into said interleaved file.
Description
RELATED APPLICATIONS
[0001] Pending U.S. patent application Ser. No. ______, entitled
"Production of a Video Stream with Synchronized Annotations over a
Computer Network", Attorney Docket Number VXT.sub.--703, assigned
to VXtreme, Inc. and filed Mar. 14, 1997, is herein incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to multimedia communications.
More particularly, the present invention relates to the delivery of
an interleaved multimedia stream over a diverse computer
network.
[0004] 2. Description of the Related Art
[0005] With the proliferation of connections to the internet by a
rapidly growing number of users, the viability of the internet as a
widely accepted medium of communication has increased
correspondingly. Bandwidth requirements can vary significantly
depending on the type of multimedia data being delivered. For
example, a low resolution, low frame rate video telephone call may
require only an ISDN connection, while a high resolution video
broadcast of a live event to a large group of viewers may require
the bandwidth of a T1 connection. Hence, the ability to deliver of
multimedia data over the internet is limited by bandwidth capacity
and cost of the network connection and also by the computational
capability of the server and client computers.
[0006] Pending patent application VXT.sub.--703 describes the
production of separate video, audio and annotation streams for
synchronous delivery from a stream server to a client computer.
However, if the stream server is not available or not affordable to
the end user at the client computer, then the client computer may
only have access to web servers which are not designed to provide
synchronous delivery capability of the separate video, audio and
annotation streams.
[0007] In view of the foregoing, there are desired techniques for
generating integrated multimedia content such as video and audio
frames, for synchronous delivery from a web server client
computer(s).
SUMMARY OF THE INVENTION
[0008] The present invention provides interleaved multimedia
streams for servers and client computers coupled to each other by a
diverse computer network which includes local area networks (LANs)
and/or wide area networks (WANs) such as the internet. Interleaved
multimedia streams can include compressed video frames for display
in a video window, accompanying compressed audio frames and
annotation frames.
[0009] In one embodiment, a producer captures separate video/audio
frames and generates an interleaved multimedia file. In another
embodiment, the interleaved file include annotation frames which
provide either pointer(s) to the event(s) of interest or include
displayable data embedded within the annotation stream.
Accordingly, each annotation frame includes either an event locator
or an event data. In addition, each annotation frame includes an
event time marker which corresponds to the time stamp(s) of
associated video frame(s) within the video stream.
[0010] The interleaved file is then stored in the web server for
subsequent retrieval by client computer(s) in a coordinated manner,
so that the client computer(s) is able to synchronously display the
video frames and displayable event(s) in a video window and event
window(s), respectively. In some embodiments, the interleaved file
includes packets with variable length fields, each of which are at
least one numerical unit in length.
[0011] These and other advantages of the present invention will
become apparent upon reading the following detailed descriptions
and studying the various figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of an exemplary computer system
for practicing the various aspects of the present invention.
[0013] FIG. 2 is a block diagram showing an exemplary hardware
environment for practicing the annotated video-on-demand (VOD)
system of the present invention.
[0014] FIG. 3A shows one embodiment of a producer which includes a
capture module and an author module.
[0015] FIG. 3B shows another embodiment of the producer in which
the capture module generates an interleaved stream.
[0016] FIG. 4A is a flowchart illustrating the capture of a live
video/audio stream from a video camera or from a previously stored
video file.
[0017] FIGS. 4B and 4C are flowcharts illustrating a locator
annotation stream and a data annotation stream, respectively.
[0018] FIG. 5 shows an exemplary format for storing and delivering
a compressed video stream.
[0019] FIG. 6 shows an exemplary customized LiveScreen display
which includes a video window, a set of VCR-like control buttons, a
selectable table of contents (TOC) and an HTML page window.
[0020] FIG. 7 illustrates an author tool provided by an author
module for the designer to visually creating annotation
streams.
[0021] FIGS. 8A and 8B are exemplary formats illustrating a locator
annotation stream and a data annotation stream, respectively.
[0022] FIG. 9A illustrates one embodiment of the client computer
which includes a web browser and a browser plug-in module for
interfacing a web browser with a client module.
[0023] FIG. 9B illustrates another embodiment of the client
computer in which the browser plug-in module receives an
interleaved stream from the web server and distributes the
video/audio stream(s) to the video/audio decoder(s) and the
annotation stream(s) to the annotation interpreter.
[0024] FIGS. 10A and 10B are flowcharts illustrating the operation
of the client module.
[0025] FIG. 11 is a flowchart illustrating the use of a table of
content with content labels enabling a viewer to skip forward or
backward to predetermined locations in the video/audio stream.
[0026] FIGS. 12A and 12B are two portions of a flowchart
illustrating the combination of video frames from a video file and
audio frames from an audio file into an interleaved file.
[0027] FIGS. 13A and 13B illustrate an exemplary format of the
interleaved file which includes a plurality of data packets for
storing video and audio frames with a variable packet length
field.
[0028] FIGS. 14A, 14B, and 14C show three exemplary formats for the
variable packet length field of FIG. 13B.
[0029] FIG. 15 is a flowchart illustrating the selection of a
suitable format for writing a packet into the interleaved file.
[0030] FIG. 16 is a flowchart illustrating the interpretation of
the exemplary variable packet length field formats of FIGS. 14A,
14B and 14C, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The present invention will now be described in detail with
reference to a few preferred embodiments thereof as illustrated in
the accompanying drawings. In the following description, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent,
however, to one skilled in the art, that the present invention may
be practiced without some or all of these specific details. In
other instances, well known process steps have not been described
in detail in order to not unnecessarily obscure the present
invention.
[0032] FIG. 1 is a block diagram of an exemplary computer system
100 for practicing the various aspects of the present invention.
Computer system 100 includes a display screen (or monitor) 104, a
printer 106, a floppy disk drive 108, a hard disk drive 110, a
network interface 112, and a keyboard 114. Computer system 100
includes a microprocessor 116, a memory bus 118, random access
memory (RAM) 120, read only memory (ROM) 122, a peripheral bus 124,
and a keyboard controller 126. Computer system 100 can be a
personal computer (such as an Apple computer, e.g., an Apple
Macintosh, an IBM personal computer, or one of the compatibles
thereof), a workstation computer (such as a Sun Microsystems or
Hewlett-Packard workstation), or some other type of computer.
[0033] Microprocessor 116 is a general purpose digital processor
which controls the operation of computer system 100. Microprocessor
116 can be a single-chip processor or can be implemented with
multiple components. Using instructions retrieved from memory,
microprocessor 116 controls the reception and manipulation of input
data and the output and display of data on output devices.
[0034] Memory bus 118 is used by microprocessor 116 to access RAM
120 and ROM 122. RAM 120 is used by microprocessor 116 as a general
storage area and as scratch-pad memory, and can also be used to
store input data and processed data. ROM 122 can be used to store
instructions or program code followed by microprocessor 116 as well
as other data.
[0035] Peripheral bus 124 is used to access the input, output, and
storage devices used by computer system 100. In the described
embodiment(s), these devices include display screen 104, printer
device 106, floppy disk drive 108, hard disk drive 110, and network
interface 112. Keyboard controller 126 is used to receive input
from keyboard 114 and send decoded symbols for each pressed key to
microprocessor 116 over bus 128.
[0036] Display screen 104 is an output device that displays images
of data provided by microprocessor 116 via peripheral bus 124 or
provided by other components in computer system 100. Printer device
106 when operating as a printer provides an image on a sheet of
paper or a similar surface. Other output devices such as a plotter,
typesetter, etc. can be used in place of, or in addition to,
printer device 106.
[0037] Floppy disk drive 108 and hard disk drive 110 can be used to
store various types of data. Floppy disk drive 108 facilitates
transporting such data to other computer systems, and hard disk
drive 110 permits fast access to large amounts of stored data.
[0038] Microprocessor 116 together with an operating system operate
to execute computer code and produce and use data. The computer
code and data may reside on RAM 120, ROM 122, or hard disk drive
120. The computer code and data could also reside on a removable
program medium and loaded or installed onto computer system 100
when needed. Removable program mediums include, for example,
CD-ROM, PC-CARD, floppy disk and magnetic tape.
[0039] Network interface circuit 112 is used to send and receive
data over a network connected to other computer systems. An
interface card or similar device and appropriate software
implemented by microprocessor 116 can be used to connect computer
system 100 to an existing network and transfer data according to
standard protocols.
[0040] Keyboard 114 is used by a user to input commands and other
instructions to computer system 100. Other types of user input
devices can also be used in conjunction with the present invention.
For example, pointing devices such as a computer mouse, a track
ball, a stylus, or a tablet can be used to manipulate a pointer on
a screen of a general-purpose computer.
[0041] The present invention can also be embodied as computer
readable code on a computer readable medium. The computer readable
medium is any data storage device that can store data which can be
thereafter be read by a computer system. Examples of the computer
readable medium include read-only memory, random-access memory,
magnetic data storage devices such as diskettes, and optical data
storage devices such as CD-ROMs. The computer readable medium can
also be distributed over a network coupled computer systems so that
the computer readable code is stored and executed in a distributed
fashion.
[0042] FIG. 2 is a block diagram showing an exemplary hardware
environment for practicing the annotated video-on-demand (VOD)
system of the present invention. The VOD system includes a
production station 210, a stream server 220, at least one web
server 230 and at least one client computer 240, each of which can
be implemented using computer system 100 described above. Stream
server 220 and web server 230 are coupled to client computer 240
via a computer network 290, e.g., the internet. Note that the
disclosed hardware environment is exemplary. For example,
production station 210 and stream server 220 can be implemented
using two separate computer systems or using one computer system.
In addition, if production station 210 and stream server 220 are
implemented on separate computer systems as shown in FIG. 2, an
optional direct connection (not shown) between production station
210 and stream server 220 can provide faster uploads of compressed
video and annotation streams. In the following description, an
audio stream optionally accompanies each video stream.
[0043] A producer 215, installed in production station 210, is a
user-friendly tool for use by a designer 219 to create a
synchronization script which includes annotation stream(s). The
annotation stream(s) define the content(s) of a LiveScreen display
245 to be displayed on client computer 240 for a viewer 249.
LiveScreen 245 display provides a graphical user interface (GUI)
with multiple windows for synchronously displaying a video stream
from stream server 220 and at least one displayable event stream.
Examples of displayable events include textual/graphical
information such as HTML-scripted web page(s) from web server
230.
[0044] In one embodiment, as shown in FIG. 3A, producer 215a
includes a capture module 317a and an author module 318a.
Production station 210 includes 16 MB of RAM and a 1 GB hard disk
drive for capturing and storing an uncompressed or precompressed
video stream. Sources for generating video streams include a video
camera 312, a video cassette recorder (VCR) (not shown) or a
previously digitized video file 314, e.g., a Video for Windows
(.avi) file. For ease of installation and use by designer 219,
producer 215a is implemented in a host environment which includes a
window-based operating system such as Microsoft Windows 95 and a
web browser such as Netscape's Navigator 3.x.
[0045] Referring also to the flowchart of FIG. 4A, in step 410
capture module 317a captures a live video/audio stream from video
camera 312 or from the previously stored video file 314. If video
camera 312 provides an analog video stream, e.g., an NTSC signal, a
hardware capture card (not shown) provides the required conversion
from the analog video stream to a digitized video stream. Because
temporary storage of uncompressed video data is memory intensive,
some form of pre-compression can be used to reduce the memory
storage requirement of the input video stream during capture step
410 and prior to compression step 420.
[0046] In step 420, capture module 420 compresses the digitized
video stream using a suitable compression technique. In this
embodiment, depending on the bandwidth capacity of the connection
provided by network 290 between stream server 220 and client
computer 240, e.g., a POTS modem, ISDN or Ethernet, a suitable
frame resolution and frame rate combination is selected. FIG. 5
shows an exemplary format 500 for storing and delivering a
compressed video stream.
[0047] A similar format can also be used to store and deliver a
separate compressed audio stream. It is also possible to combine,
e.g., interleave a compressed video and audio data into one stream
for delivery. Audio encoders/decoders (codecs) are available from a
number of commercial sources. Examples include ToolVox from Voxware
Inc., 305 College Road East, Princeton, N.J. 08540, and QCELP from
QUALCOMM Inc., 10555 Sorrento Valley Road, San Diego, Calif.
92121.
[0048] Referring back to FIGS. 3A and 4A, in step 430, designer 219
uses author module 318a to compose a suitable LiveScreen display
format which defines the layout of LiveScreen display 245 at client
computer 240. FIG. 6 shows an exemplary customized LiveScreen
display 600 which includes a video window 610, a set of VCR-like
control buttons 620, a selectable table of contents (TOC) 630 and
an HTML page window 640. Examples of other displayable event
windows include but is not limited to ticker tape windows (not
shown). In this implementation, LiveScreen templates 319 are
available for designer 219 to use as starting points for composing
customized LiveScreen formats.
[0049] FIG. 7 illustrates an author tool 700 provided by author
module 318a for designer 219 to visually creating annotation
streams (step 440). There are two types of annotation streams. The
first type of annotation streams are data annotation streams in
which the displayable event data are embedded within the annotation
streams. Examples of data annotation streams include ticker
annotation streams which include ticker tape data embedded within
the annotation stream. The second type of annotation streams are
locator annotation streams in which the displayable data is either
too cumbersome and/or is continually evolving to be embedded as
static data within the annotation stream. Instead, event locator(s)
pointing to the location of the displayable data are stored in the
annotation streams instead of the displayable data. Examples
include URL addresses pointing to HTML pages.
[0050] Designer 219 may view frames from video stream 500 displayed
in video window 720 for referencing and selecting appropriate time
stamps to use in generating annotation streams. Within video window
720, VCR function buttons, e.g., a rewind button 724, a play button
726 and a fast forward button 728, are available for designer 219
to quickly traverse video stream 500. Since video window 720 is
provided as a convenience for designer 219, if designer 219 has
prior knowledge of the content of the video stream, designer 219
may proceed with the generation of the annotation streams without
viewing video window 720.
[0051] As shown in FIG. 7, author tool 700 displays a flipper time
track 750, a video time track 760, an audio time track 770, a
ticker time track 780 and a table of contents (TOC) time track 790.
Flipper time track 750 and ticker time track 780 aid designer 217
in generating a flipper annotation stream and a ticker annotation
stream, respectively. Another visual control aid, zoom bar 716,
enables designer 219 to select the respective portions of the
complete time tracks 750, 760, 770, 780 and 790, as defined by
start time indicator 712 and end time indicator 718, which is
currently displayed by author tool 700.
[0052] In accordance with one aspect of the invention, annotation
frames are generated by designer 217 to form customized annotation
streams (step 440). A time hairline 715 spanning time tracks 750,
760, 770, 780 and 790 provides designer 217 with a visual aid to
select an appropriate time, displayed in time indicator 714, for
synchronizing a displayable event. The exemplary format of time
indicators 712, 714 and 718 are "hours:minutes:seconds".
[0053] FIGS. 4B and 8A are a flowchart and an exemplary format,
respectively, illustrating a locator annotation stream 800a.
Locator annotation stream 800a includes an annotation stream header
810a, and a plurality of annotation frames 820a, 830a, 840a, . . .
890a. Each annotation frame includes an event locator and an event
time marker, e.g., annotation frame 820a includes event locator
822a and event time marker 824a. One example of a locator
annotation stream is a flipper stream. Flipper time track 750
provides a convenient way to select suitable event time marker
values, e.g., flipper time markers 751, 752, 753, 754, for the
respective event locators. For example, URL addresses (event
locators) pointing to HTML pages enable client computer 240 to
subsequently retrieve textual and/or graphical elements to be
displayed at predetermined time as defined by the time markers of
the flipper stream.
[0054] FIGS. 4C and 8B are a flowchart and an exemplary format,
respectively, illustrating a data annotation stream 800b. Locator
annotation stream 800a includes an annotation stream header 810a,
and a plurality of annotation frames 820a, 830a, 840a, . . . 890a.
Each annotation frame includes an event locator and an event time
marker, e.g., annotation frame 820a includes event locator 822a and
event time marker 824a. One example of a data annotation stream is
a ticker stream. The generation of the ticker stream is somewhat
similar to that of the flipper stream. However, in the case of the
ticker stream, instead of event locators, displayable data is
embedded directly into the ticker stream as event data.
[0055] When author module 318a has completed building an annotation
stream, e.g., the flipper stream, the annotation stream is given a
file name and loaded into a convenient server, e.g., stream server
220, for subsequent retrieval by client computer 240. The use of
the annotation streams is described in greater detail below with
the description of client computer 240.
[0056] In accordance with another aspect of the invention,
LiveScreen display 600 also includes a table of contents (TOC) 630,
enabling viewer 249 at client computer 240 to skip forward or
backward to a point within the entire video/audio stream 500. TOC
630 include one or more content labels, each indexed to a
corresponding time stamp in video stream 500, as defined by TOC
time markers 791, 792, 793, 794 in LiveScreen display 600.
[0057] Referring now to FIG. 9A, in one embodiment of the present
invention, client computer 240 includes a web browser 950 and a
browser plug-in module 952a for interfacing web browser 950 with a
main client module 960. Client module 960 includes an event
registry 962, playout buffer(s) 966, video/audio decoder(s) 964,
video/audio renderer(s) 965 and one or more dynamically loadable
event applet(s), e.g., flipper applet 967, ticker applet 968 and
VCR applet 969. In this embodiment, event registry 962 also
functions as an annotation interpreter 963.
[0058] FIG. 10A is a flowchart illustrating the operation of client
module 960. Assume that viewer 249 has not previously loaded client
module 960 in client computer 240, but has already loaded a web
browser 950, e.g., Netscape's Navigator (step 1010). Viewer 249
surfs the world-wide web (www) via the internet and locates a web
site of interest to viewer 249. Typically, the web site of interest
is hosted on web server 230. Accordingly, a target web page is
downloaded from web server 230 and displayed on client computer
240.
[0059] The target web page includes a link to a customized
LiveScreen display, e.g., display 600. If client module 960 has not
been previously loaded, client module 960 is now loaded over web
browser 950 for processing video/audio and annotation streams (step
1020). Depending on the implementation, a copy of client module 960
may be available from the web site of interest. Alternatively, the
target web page may provide a HTML link to another web server which
has an updated copy of client module 960.
[0060] Referring now to FIG. 10B, first, browser plug-in module
952a is installed over web browser 950 (step 1022). As discussed
above, plug-in module 952a provides the interface between client
module 960 and web browser 950. The target web page provides a HTML
link to the format for LiveScreen display 600. The LiveScreen
display format is retrieved and display 600 is installed on client
computer 240 using web browser 950 (step 1024).
[0061] Next, event registry 962 begins a registration/load process
of the event applets, e.g., flipper applet 967, ticker applet 968
and VCR applet 969 (step 1026). Event registry 962 is capable of
dynamically registering event applets, i.e., registry 962 is
capable of registering additional event applets after the initial
registration process, thereby making it possible to add new event
windows to LiveScreen display 600 of client computer 240 without
having to re-install client module 960. Each event applet has a tag
which includes attributes such as Java class, command stream format
RTP://server name and file name (location of stream). During the
registration process, each applet provides event registry 962 with
a list of its respective function(s).
[0062] Referring back to FIG. 10A, encoded video/audio frames and
associated annotation frames are streamed from stream server 220 to
client computer 240 for synchronous display (step 1030). Streaming
video and audio streams over a network is very efficient because
streaming eliminates the need for a large buffer at client computer
240. In addition, streaming also provides flexibility, e.g.,
switching video sources midstream is possible without wasting
network resources since streaming is based on a pseudo just-in-time
(JIT) protocol and does not involve downloads of the entire video
stream prior to display at client computer 240. If the underlying
transmission protocol is HTTP, then video, audio and annotation
packets are initially "pulled" by client computer 240 from server
220 using HTTP "get" packet(s).
[0063] Next, the encoded video/audio streams are decoded by decoder
964, i.e., decompressed using a suitable technique, and then
displayed at client computer 240 by renderer 965 (step 1040).
[0064] In this implementation, annotation frames streamed from
stream server 220 are encoded in Visual Basic script. As shown in
FIGS. 8A and 8B, annotation streams 800a, 800b include stream
headers 810a, 810b, respectively, followed by one or more
annotation frames. Annotation interpreter 963 parses annotation
frames in real-time in the form of messages from stream server 220,
and converts the messages into a C++ function calls for the
respective event applets (step 1050). In the case of flipper stream
800a, each annotation frame includes a HTML address and an event
time marker. In the case of ticker stream 800b, each annotation
frame includes ticker data and an event time marker. Note that an
event time marker need not be identical to a corresponding video
time stamp. Client computer 240 is capable of switching to a new
displayable event together with a video frame or in between two
video frames.
[0065] While the contents of annotation frames may differ, from the
perspective of stream streamer 220, the event data or event locator
are simply arguments to be passed on to client computer 240 to be
processed by client computer 240. Hence, all annotation frames are
processed in the same manner by stream server 220, i.e., annotation
frames are streamed to client computer 240 at the appropriate time
in accordance with their respective event time markers.
[0066] Further, since the video and annotation streams are handled
synchronously but separately by video decoder 964 and annotation
interpreter 963, respectively, steps 1040 and 1050 can occur
concurrently or consecutively. As discussed above, event registry
962 is capable of dynamic registration of event applets.
Accordingly, annotation interpreter 963 is adaptable, and capable
of automatic installation and linking of new event applet(s) to add
new class(es) of displayable events for client computer 240.
[0067] After registering with event registry 962, flipper applet
967 provides the location of the flipper stream to broswer 950
which then begin receiving the flipper stream from stream server
220. Flipper annotation frames are provided by stream server 220
synchronously with the video/audio frames to client module 960 so
that the annotations, i.e., displayable events can be synchronized
for display at client computer 240 (step 1060). In this example,
URL addresses, for synchronizing HTML page flips with video stream
are provided to web broswer 950 thereby permitting client computer
240 to subsequently retrieve and display various textual and
graphical elements changing at predetermined points corresponding
to the timeline of the video stream. Note that HTML pages can be
retrieved from one or more web server(s) 230.
[0068] Similarly, after registering with event registry 962, ticker
(tape) applet 968 provides the location of the ticker stream to
broswer 950 which then begins receiving the ticker stream from
stream server 220. Ticker annotation frames are provided by stream
server 220 synchronously with the video/audio frames so that the
annotations, i.e., displayable ticker data can be synchronized for
display at client computer 240 at predetermined points
corresponding to the timeline of the video stream.
[0069] Many types and combinations of display windows and/or
content are possible. For example, another window may be used to
display documents delivered via a data annotation stream and a
"PowerPoint" viewer. Another exemplary variation includes providing
an annotation stream to an "ActiveX" object for viewing displayable
event(s) associated with a HTML page.
[0070] After registration, VCR control applet 969 provides VCR-like
control buttons 620 such as play, rewind, fast forward, pause, and
live-play. Note that since VCR buttons are under the interactive
control of viewer 249, activation points in the time line cannot be
predicted in advance, and so no annotation stream is used. Instead,
when a VCR-type function such as rewind ("REW") is activated, VCR
applet 969 sends an appropriate message is sent to stream server
220, which resets both the video/audio streams and annotation
stream(s) to the viewer selected point in time.
[0071] As shown in FIG. 11, a table of content 630 with content
labels enables viewer 249 to skip forward or backward to
predetermined locations in the video/audio stream. First, viewer
249 selects a content label of interest (step 1110). Examples of
suitable content labels are section headings of the video stream.
Next, client module 960 sends a message to stream server 220 with
the time stamp of an I-frame from the video stream whose location
is close to selected content label (step 1120). In this embodiment,
an I-frame is a video frame which includes data for a complete
video frame. Although computationally more intensive, it is also
possible to select a P-frame and then reconstructed a complete
video starting from a neighboring I-frame close to the selected
P-frame.
[0072] In step 1130, stream server 220 resets the video/audio
stream and the annotation stream(s) to correspond to the selected
I-frame. Stream server 220 is now ready to resume transmission of
the video/audio stream and the annotation stream(s) to client
computer 240 for viewing (step 1140).
[0073] Referring now to FIGS. 3B and 9B, in another embodiment,
instead of streaming three separate video, audio and annotation
streams from stream server 220 to client computer 240, an
interleaved video/audio/annotation file is produced by producer
215b, stored in web server 230, and subsequently provided to client
module 960 on demand via web browser 950. Note that an interleaved
file can include any two or more frame types, e.g., video and audio
frames, video and annotation frames, or audio and annotation
frames.
[0074] Advantages of this embodiment include simplified synchronous
delivery of video, audio and annotation frames to client computer
240. Simplicity is accomplished by eliminating the need for stream
server 220, whose primary function is to manage the transmission of
several separate video, audio and annotation streams from stream
server 220 to client computer 240. In this embodiment, since all
the video, audio and annotation frames are combined into a single
interleaved stream and are pre-sorted by timestamp values, the
interleaved stream can now be stored in web server 230 and
delivered in the form of HTTP data.
[0075] FIGS. 12A and 12B are two portions of a flowchart
illustrating the combination of video frames from a video file and
audio frames from an audio file into an interleaved file by
producer 215b. First, the audioframe and videoframe buffers are
initialized to "null" (step 1210). Note that null can be
represented by any one of a variety of ways known to one skilled in
the art.
[0076] In step 1222, if the audioframe buffer is empty, i.e., set
to null, then producer 215b retrieves the next audio frame from the
audio file (step 1224). If the retrieval is successful (step 1226),
then the audiotimestamp is set to the timestamp of the retrieved
audio frame (step 1228).
[0077] In step 1232, if the videoframe buffer is empty, i.e., set
to null, then producer 215b retrieves the next video frame from the
video file (step 1234). If the retrieval is successful (step 1236),
then the videotimestamp is set to the timestamp of the retrieved
video frame (step 1238).
[0078] If both the audioframe and videoframe buffers are full and
the audiotimestamp is less than or equal to the videotimestamp, OR
if the audiotimestamp is full and the videotimestamp is empty (step
1252), then producer 215b writes the audio frame in the audioframe
buffer to the interleaved file, sets the audioframe buffer to null,
and returns (1270) to step 1222 (step 1254).
[0079] If both the audioframe and videoframe buffers are full and
the videotimestamp is less than or equal to the audiotimestamp, OR
if the videotimestamp is full and the audiotimestamp is empty (step
1262), then producer 215b writes the video frame in the videoframe
buffer to the interleaved file, sets the videoframe buffer to null,
and returns (1270) to step 1222 (step 1264).
[0080] Eventually, both audioframe and videoframe buffers will be
empty again and results of steps 1252 and 1262 will both be
negative, indicating that all the frames in both video and audio
files are been processed, and the interleaved video and audio file
is now complete. The above described algorithm for generating an
interleaved file from two input files can be adapted to generating
an interleaved file from three or more input files, e.g., by adding
the appropriate number of buffers, one for each additional input
file.
[0081] In accordance with another aspect of this embodiment, the
data packets 1320, 1330, . . . 1390 for streaming video and audio
frames include a variable packet length field 1324 as shown in
FIGS. 13A and 13B. Referring to FIGS. 14A, 14B, and 14C, three
exemplary formats 1324a, 1324b, and 1324c of the variable packet
length field 1324 are shown. In this implementation, the length of
the variable packet length field is in multiples of number units.
For example, formats 1324a, 1324b and 1324c can be one numerical
unit in length, three numerical units in length and seven numerical
units in length, respectively. As is known to one skilled in the
art, regardless of the size of the packet length field, the packet
length can be represented by a number of different methods, such as
simple binary, one's complement, BCD and floating point.
[0082] FIG. 15 is a flowchart illustrating the selection of a
suitable format for writing a packet into the interleaved file. If
the size of packet length 1324 is less than one numerical unit
(step 1510), then the first format 1324a (FIG. 14A) with one
numerical unit length is sufficient to store packet length 1324
(step 1520).
[0083] Else if the size of packet length 1324 between one numerical
unit (step 1510) and two numerical units (step 1530), then a null
number, one numerical unit in size, is written (step 1540). As
discussed above, null can be represented in any one of a number of
ways known to one skilled in the art. Next, producer 215b writes
packet length 1324 up to two numerical units in size as shown in
FIG. 14B (step 1545).
[0084] Else if the size of packet length 1324 is greater than two
numerical units (step 1530), then three null numbers, each one
numerical unit in size, are written (step 1550). Next, producer
215b writes packet length 1324 up to four numerical units in size
as shown in FIG. 14C (step 1555).
[0085] FIG. 16 is a flowchart illustrating the interpretation of
the variable packet length field formats 1324a, 1324b, and 1324c of
FIGS. 14A, 14B and 14C, respectively. If the first number (one
numeral unit in size) is not null (step 1610), then the first
number is the value of variable packet length 1324 (step 1620).
[0086] Else if the first number is null, but the second number and
the third number are not both null (steps 1610 and 1630), then the
second number and the third number represent the value of variable
packet length 1324 (step 1640).
[0087] Else if the first, second and third numbers are all null
(steps 1610 and 1630), then the fourth, fifth, sixth and seventh
numbers represent the value of variable packet length 1324 (step
1640).
[0088] Many variations of this embodiment are also possible. For
example, capture module 317b may generate separate compressed video
files and audio files and leave the entire interleaving step to
author module 318b which receives the separate video and audio
frames, generates the annotation frames, and then combines the
video, audio and annotation frames into an interleaved file.
Modifications are also possible in client module 960. For example,
instead of tasking browser plug-in module 952b with the separation
of the interleaved stream into its component video and audio frames
and annotation messages, browser plug-in module 952b may pass on
the interleaved stream to client module 960 which then separates
the interleaved stream into its component frames.
[0089] While this invention has been described in terms of several
preferred embodiments, there are alterations, permutations, and
equivalents which fall within the scope of this invention. For
example, although the present invention is described using video,
audio and annotation frames, the methods and apparatuses of the
present invention are equally applicable other multimedia frames.
It is therefore intended that the following appended claims be
interpreted as including all such alterations, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
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