U.S. patent application number 14/551869 was filed with the patent office on 2016-11-10 for method and system for determining a quality value of a video stream.
The applicant listed for this patent is Telefonaktiebolaget LM Ericsson (Publ). Invention is credited to Jorgen Gustafsson, David Lindegren, Martin Pettersson.
Application Number | 20160330484 14/551869 |
Document ID | / |
Family ID | 40810500 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160330484 |
Kind Code |
A9 |
Gustafsson; Jorgen ; et
al. |
November 10, 2016 |
Method and System for Determining a Quality Value of a Video
Stream
Abstract
Hence a method is provided for determining a quality value of a
video stream, comprising the steps of: identifying lost data
packets of the video stream; identifying at least two intra coded
frames of the video stream; determining intra coded frames having a
maintained image quality, based on estimating if a lost data packet
is associated with an intra coded frame; estimating a distance
between each one of the lost data packets and a next respective,
subsequent intra coded frame having a maintained image quality; and
generating the quality value, based on the distances. A system and
a computer readable medium are also described.
Inventors: |
Gustafsson; Jorgen; (Lulea,
SE) ; Lindegren; David; (Lulea, SE) ;
Pettersson; Martin; (Vallentuna, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget LM Ericsson (Publ) |
Stockholm |
|
SE |
|
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Prior
Publication: |
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Document Identifier |
Publication Date |
|
US 20150215649 A1 |
July 30, 2015 |
|
|
Family ID: |
40810500 |
Appl. No.: |
14/551869 |
Filed: |
November 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13127285 |
May 3, 2011 |
8923411 |
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PCT/EP2008/064959 |
Nov 4, 2008 |
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14551869 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 17/004 20130101;
H04N 19/154 20141101; H04N 19/89 20141101; H04N 19/159 20141101;
H04L 43/0835 20130101; H04N 19/521 20141101; H04N 19/46 20141101;
H04N 19/66 20141101 |
International
Class: |
H04N 19/66 20060101
H04N019/66; H04N 19/513 20060101 H04N019/513; H04L 12/26 20060101
H04L012/26 |
Claims
1-19. (canceled)
20. A method of determining a quality value of a video stream
transmitted to a media player, the method comprising, for a
measuring interval of the video stream: identifying at least two
lost data packets of the video stream, identifying intra coded
frames of the video stream, determining, for each of the intra
coded frames identified, that the intra coded frame has a
maintained image quality if none of the lost data packets
identified are associated with the intra coded frame, estimating,
for each of the lost data packets identified, a distance between
that lost data packet and the next intra coded frame that occurs
subsequently to the lost data packet in the video stream and that
has a maintained image quality, and generating the quality value,
based on the distances.
21. The method according to claim 20, wherein generating the
quality value based on the distances comprises weighting the
distances.
22. The method according to claim 21, wherein said weighting
comprises weighting a relatively longer distance higher than
weighting a relatively shorter distance.
23. The method according to claim 22, wherein the relatively longer
distance and the relatively shorter distance are estimated for a
common intra coded frame.
24. The method according to claim 21, wherein said weighting
comprises weighting an estimated distance of a lost data packet
associated with an intra coded frame of the video stream relatively
higher than weighting an estimated distance of a lost data packet
associated with a predicted image frame of the video stream.
25. The method according to claim 21, wherein said weighting
comprises weighting distances of two data packets associated with a
common image frame higher than weighting distances of two data
packets associated with different image frames.
26. The method according to claim 20, wherein the data packets are
defined by a real-time transport protocol comprising a marker bit,
and wherein identifying an intra coded frame of the video stream
comprises identifying an image frame of the video stream as an
intra coded frame based on a marker bit value of a data packet of
the image frame.
27. The method according to claim 20, wherein identifying an intra
coded frame of the video stream comprises identifying an image
frame of the video stream as an intra coded frame based on whether
or not an image size of the image frame is a factor larger than an
image size of an average image frame.
28. The method according to claim 20, wherein generating the
quality value is based on a data packet loss rate.
29. A system for determining a quality value of a video stream
transmitted to that media player, the system configured to, for a
measuring interval of the video stream: identify at least two lost
data packets of the video stream, identify intra coded frames of
the video stream, determine, for each of the intra coded frames
identified, that the intra coded frame has a maintained image
quality if none of the lost data packets identified are associated
with the intra coded frame, estimate, for each of the lost data
packets identified, a distance between that lost data packet and
the next intra coded frame that occurs subsequently to the lost
data packet in the video stream and that has a maintained image
quality, and generate the quality value, based on the
distances.
30. The system according to claim 29, wherein the system is
configured to generate the quality value based on the distances by
weighting the distances.
31. The system according to claim 30, wherein the system is
configured to weight a relatively longer distance higher than
weighting a relatively shorter distance.
32. The system according to claim 31, wherein the relatively longer
distance and the relatively shorter distance are estimated for a
common intra coded frame.
33. The system according to claim 30, wherein the system is
configured to weight an estimated distance of a lost data packet
associated with an intra coded frame of the video stream relatively
higher than weighting an estimated distance of a lost data packet
associated with a predicted image frame of the video stream.
34. The system according to claim 30, wherein the system is
configured to weight distances of two data packets associated with
a common image frame higher than weighting distances of two data
packets associated with different image frames.
35. The system according to claim 29, wherein the data packets are
defined by a real-time transport protocol comprising a marker bit,
and wherein the system is configured to identify an image frame of
the video stream as an intra coded frame based on a marker bit
value of a data packet of the image frame.
36. The system according to claim 29, wherein the system is
configured to identify an image frame of the video stream as an
intra coded frame based on whether or not an image size of the
image frame is a factor larger than an image size of an average
image frame.
37. The system according to claim 29, wherein the system is
configured to generate the quality value based on a data packet
loss rate.
38. A computer program product stored on a computer readable medium
and comprising a computer program having software instructions
that, when run on a computer associated with a system, cause the
system to determine a quality value of a video stream transmitted
to the media player, the software instructions causing the system
to, for a measuring interval of the video stream: identify at least
two lost data packets of the video stream, identify intra coded
frames of the video stream, determine, for each of the intra coded
frames identified, that the intra coded frame has a maintained
image quality if none of the lost data packets identified are
associated with the intra coded frame, estimate, for each of the
lost data packets identified, a distance between that lost data
packet and the next intra coded frame that occurs subsequently to
the lost data packet in the video stream and that has a maintained
image quality, and generate the quality value, based on the
distances.
Description
TECHNICAL FIELD
[0001] The invention relates to a method, system and computer
readable medium for determining a quality value of a video
stream.
BACKGROUND
[0002] Today new radio networks have enabled more bitrate-heavy
services such as streamed multimedia (video) content and mobile TV.
At the same time TV over Internet Protocol (IP) has become a
popular service in fixed communication networks. Along with this
development there has been a growing emphasis on real-time
assessment of video quality for this kind of visual communication
services. The methods for video quality assessment include
subjective methods and objective methods. The subjective methods
typically involve human assessors, who grade or score video quality
based on their subjective feelings, and use the grades or scores
obtained in such a subjective way for video quality assessment. The
objective methods, on the other hand, do not involve human
assessors and assess the video quality only by using information
obtained from the video sequences.
[0003] The objective video quality assessment methods can be
further classified into full-reference methods, reduced-reference
methods, and no-reference methods. Full reference models are
available on the market and, for example, include Perceptual
Evaluation of Video Quality by OPTICOM, Optimacy tool from Genista
Corporation and products from Psytechnics Ltd and National
Telecommunications and Information Administration.
[0004] Both the full-reference methods and the reduced-reference
methods need reference information about the original video (i.e.
the video actually transmitted from the transmitting side) to
conduct the video quality assessment and thus cannot be used for
real-time in-service video quality assessment. On the other hand,
the no-reference methods do not require the reference information
of the original video. Instead, the no-reference methods make
observations only on decoded video (i.e. the video that has been
received and decoded on the receiving side) and estimate the video
quality using only the observed information on the decoded
video.
[0005] For a no-reference video quality assessment, two major
sources of video quality decline should be taken into
consideration. The first one is coding and compression of video
sources and the second one is data packet loss during transmission,
i.e. during the streaming of the video content. Another source of
video quality decline may be so called packet jitter.
[0006] In an IP network, deterioration in perceived video quality
is typically caused by data packet loss. Most packet losses result
from congestions in network nodes as more and more packets are
dropped off by routers in IP networks when congestion occurs and
the severity increases. In case of a wireless communication
network, poor radio conditions may cause packet loss. The effect of
packet loss is a major problem for real-time video transmission
(streaming video). The measurement of the video quality decline
caused by packet loss during transmission is referred to as packet
loss metric.
[0007] The streamed video is typically coded and compressed by
using codecs such as, for example, H.263, MPEG-4, H.264 and VC-1,
that utilize temporal predictive coding to improve coding
efficiency. Three types of frames are then commonly used: a) intra
frames (I-frames) that do not use temporal prediction and serves as
a video refresh frame, b) predictive frames (P-frames) and c)
bi-predictive frames (B-frames) that are predicted from one or more
reference frames. Here, I-frames and P-frames usually act as
reference frames, and if a part of a reference frame is lost an
error resulting from the loss tends to propagate in time until the
next I-frame (or P-frame) refreshes the video.
[0008] A number of prior methods for calculating video
deterioration due to packet loss have been proposed, of which one
is based on estimating a number of lost macro-blocks for each frame
type of a video stream. Another technique extracts spatial
distortion of each image in a video stream using differences
between corresponding regions of two adjacent frames in the video
sequence. The spatial distortion is weighted based on temporal
activities of the video, and the video quality is measured by
detecting the spatial distortions of all images in the
sequence.
[0009] However, the aforementioned methods for calculating video
deterioration needs to process all the blocks in the image frames,
which means that those methods are very computational intensive and
are not optimal for use in many real time video transmissions
applications.
SUMMARY
[0010] In view of the foregoing, it is an object of the invention
to provide an improvement of the above techniques and prior art.
More particularly, it is an object to provide a parametric
(no-reference) method for estimating quality of streaming video,
which method requires little computational effort.
[0011] Hence a method is provided for determining a quality value
of a video stream transmitted to a media player. The method
comprises the steps of, for a measuring interval of the video
stream: identifying at least two lost data packets of the video
stream; identifying intra coded frames of the video stream;
determining which of the intra coded frames that have a maintained
image quality, based on estimating if a lost data packet is
associated with an intra coded frame; estimating a distance between
each one of the lost data packets and a next respective, subsequent
intra coded frame having a maintained image quality; and generating
the quality value, based on the distances.
[0012] In further detail, the quality value is determined for a
measuring interval that can be set as a parameter. For example, the
measuring interval may be a time interval, or a number of
sequential data packets or a number of sequential picture frames of
the video stream. "Lost data packets" also includes any data packet
that is not necessarily lost per se but contains information that
is corrupt to such an extent that the information of the data
packet may not be fully retrieved.
[0013] It should also be noted that an intra coded frame is, in
this context, a frame which is used as a reference frame for other
frames, which means that the video is a compressed video that
comprises some picture frames that require the prior decoding of
some other picture frame(s) in order to be decoded. As known within
the art, data forming the picture frames are contained in data
packets of the video stream.
[0014] Since data packets and frames of the video stream are
sequential and since it is possible to tie a data packet to a video
frame, the distance between a lost packet and an intra frame may be
given by a time value, or by a number of data packets or by a
number of picture frames. This is quite advantageous in that the
required calculations for the distance determining are quite fast
and straightforward, which means that little computational effort
is required by a computer device that performs the method.
[0015] Here, a frame that has a "maintained image quality" is a
frame for which no information have been lost during transport.
[0016] The generating of the quality value may comprise weighting
of the distances, which is quite advantageous in that the video
quality experienced by a user may not always be linear with the
distance from a corrupt data packet to an intra coded frame. By
using weighting, less computational effort is needed in comparison
with known technologies, as weighting is a quick operation and
allows for a generation of a more subjectively reliable quality
value.
[0017] The weighting of a long distance of the distances may be
higher than the weighting of a shorter distance of the distances,
which produces a more reliable quality value as a user often
registers low video quality only after some time, i.e. when the
distance from the lost data packet to the intra coded frame is
long.
[0018] The long distance and the shorter distance may be estimated
for a common intra coded frame, which is particularly relevant
since the intra coded frame refreshes the video image.
[0019] The weighting of an estimated distance of a lost data packet
associated with an intra coded frame may be relatively higher than
the weighting of an estimated distance of a lost data packet
associated with a predicted image frame of the video stream, which
gives a more reliable quality value since an error in an intra
coded frame propagates to the next intra coded frame with a
maintained image quality. This weighting is also useful since intra
coded frames are added when there is a scene change, and a quality
loss in a scene changing intra coded frame will cause the error to
be very visible.
[0020] The weighting of distances of two data packets associated
with a common image frame may be higher than the weighting of
distances of two data packets associated with different image
frames, which give a more reliable quality value since many lost
data packets for the same image frame significantly reduces the
subjectively experienced video quality.
[0021] The data packets may be defined by a real-time transport
protocol comprising a marker bit, and an image frame of the video
stream may be identified as an intra coded frame in dependence of a
marker bit value of a data packet of the image frame, which
provides for a computationally efficient image identification
process.
[0022] An image frame of the video stream may be identified as an
intra coded frame in dependence of if an image size of the image
frame is a factor larger than an image size of an average image
frame, which, from a computational point of view, increases the
efficiency of the method.
[0023] The generating of the quality value may be based on a data
packet loss rate. Typically data packet loss rate is the relation
between the number of lost data packets and the total number of
transmitted data packets (during the measure interval).
[0024] According to another aspect of the invention, a system is
provided for determining a quality value of a video stream
transmitted to a media player. The system is configured to, for a
measuring interval of the video stream: identify at least two lost
data packets of the video stream; identify intra coded frames of
the video stream; determine which of the intra coded frames that
have a maintained image quality, based on estimating if a lost data
packet is associated with an intra coded frame; estimate a distance
between each one of the lost data packets and a next respective,
subsequent intra coded frame having a maintained image quality; and
generate the quality value, based on the distances.
[0025] According to yet another aspect of the invention, a computer
readable medium is provided, having stored thereon a computer
program having software instructions which when run on a computer
cause the computer to, for a measuring interval of a video stream,
perform the steps of: identifying at least two lost data packets of
the video stream; identifying intra coded frames of the video
stream; determining which of the intra coded frames that have a
maintained image quality, based on estimating if a lost data packet
is associated with an intra coded frame; estimating a distance
between each one of the lost data packets and a next respective,
subsequent intra coded frame having a maintained image quality; and
generating the quality value, based on the distances.
[0026] The inventive system and computer readable medium may
comprise, be configured to execute and/or having stored software
instructions for performing any of the features described above in
association with the inventive method, and has the corresponding
advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Embodiments of the invention will now be described, by way
of example, with reference to the accompanying schematic drawings,
in which
[0028] FIG. 1 illustrates a system implementing the invention,
[0029] FIG. 2 is a schematic view of a media player,
[0030] FIG. 3 is a schematic view of a video stream, and
[0031] FIG. 4 is a flow diagram of an embodiment of the inventive
method.
DETAILED DESCRIPTION
[0032] With reference to FIG. 1 a system implementing the invention
is illustrated and comprises a media (video) content server 112
that is connected to a database 113 on which media content such as
compressed video is stored. The media content server 112 is, via a
network 111, connected to a number of media players such as a TV
114, a mobile phone 115 and a personal computer 116 or any other
electronic device capable of receiving and playing streaming video.
The media content server 112 is configured to send a compressed
video stream via the network 111 to the media players 114, 115, 116
which in turn are configured to receive and decode the video stream
such that a video content of the stream may be played by the media
players 114, 115, 116.
[0033] Sending, receiving and decoding are here done in a
conventional manner and all involved devices implements a suitable,
known network protocol that supports streaming video.
[0034] In further detail, FIG. 2 illustrates a media player 211
that is connected (not shown) to the media content server 112 via
the network 111. The media player 211 comprises a processor 212
which is connected to a computer readable medium 213, here in the
form of a non-volatile memory such as a hard disk, ROM (Read-Only
Memory) and a flash memory, having stored thereon a computer
program 214. The computer program 214 comprises software
instructions which when run on the media player causes the media
player 211 to make the method steps described below. A
communications interface 215 is also connected to the processor 212
for providing communication with the media content server 112 via
the network 111.
[0035] The media player 211 also comprises means and software
instructions (not shown) for receiving and decoding the video
stream and subsequently play the video content of the video
stream.
[0036] As mentioned, the media content server 112 and media players
114, 115, 116, 211 mutually communicate and operate in a
conventional, known manner. In particular, the devices may
implement the "RTP Transport Protocol for Real-Time Applications"
in accordance with the Request for Comment no. 3550 (RFC 3550). Of
course, it is possible to use other protocols when implementing the
inventive method and system, e.g. the transport protocols MPEG2-TS
and MPEG4-TS. In any case, this means that the video stream sent to
the media players comprises data packets for the transportation of
the data content of the video stream.
[0037] As described, the video stream transports video that is
compressed by a compression codec (encode-decode scheme) such as
H.263, MPEG-4, H.264 and VC-1. This means that a picture frame of
the video stream is compressed using different algorithms in
dependence of what compression codec is used.
[0038] As a result, the different algorithms for video frames gives
different picture types or frame types of the video stream, and
three major picture types are used, i.e. I-frames (Intra coded
frames), P-frames (Predicted frames) and B-frames (Bi-directional
predicted frames). As known within the art, I-frames are the least
compressible but don't require other video frames to decode.
P-frames can use data from previous frames to decompress and are
more compressible than I-frames, while B-frames can use both
previous and forward frames for data reference to get an even
higher amount of data compression. Of course, it is sufficient to
have only one type of intra coded frame (e.g. the I-frame) and one
type of predicted image frame (e.g. the P-frame or the
B-frame).
[0039] With reference to FIG. 3 a portion of the video stream S is
illustrated, which portion is defined by a measuring interval
.DELTA.T of the video stream S. The measure interval .DELTA.T is in
turn defined by a start time and a stop time and the video stream S
then comprises all data packets received by the media player
between the start time and the stop time. It is also possible to
define the measure interval .DELTA.T by a number of subsequent data
packets or by a number of subsequent picture frames of the video
stream S.
[0040] In any case, the measure interval .DELTA.T of the video
stream comprises, in this example, 16 data packets 1-16. These
packets 1-16 contains data in the form of 12 picture frames I1, P1,
P2, 12, P3, P4, 13, P5, P6, I4, P7 and P8. Here, an intra coded
frame I1, I2, I3, I4 is contained in two data packets while a
predicted frame P1, P2, P3, P4, P5, P6, P7, P8 is contained in one
data packet. This is due to the fact that an intra code frame
typically is much larger than a predicted frame, in terms of the
amount of data needed for creating the frames. The data packets
1-16 are distributed over the measure interval .DELTA.T and since
the data forming the frames are contained in the data packets the
frames are also distributed over the measure interval .DELTA.T.
Data packets that are lost during the streaming process, in this
example the packets 3, 4, 7, 8, 9, are illustrated with dashed
lines.
[0041] Each data packet contains information about a) its sequence
number i in the video stream, b) an image frame number j (derived
from time stamp) the packet belongs to, and c) if the data packet
is the last packet of an image frame. Typically, a so called marker
bit value (M-bit value) of a data packet indicates whether the data
packet is the last packet of a frame. It may also be that the
marker bit value indicates whether the data packet is the first
packet of a frame, depending on what transport format is used.
[0042] Accordingly, in this example, the stream sequence number of
the first data packet 1 is i, the stream sequence number of the
second data packet 2 is i+1 and so on. Data packets 1 and 2 each
have a same image frame number j since they belong to the same
image frame while data packet 3 has, or more specifically had since
the packet 3 was lost, a frame number of j+1 since it belong to the
next frame. Data packet 1 has an M-value of "0" indicating it is
not the last packet for the frame I1, while data packet 2 has an
M-value of "1" indicating it is the last data packet of the frame
I1. To summarize, the data packets comprise (or should have
comprised if the packet was not lost) the following
information:
TABLE-US-00001 Sequence no. Image frame Data packet (SeqNo) no.
M-bit value Size in bytes 1 i j 0 1200 2 i + 1 j 1 705 3 i + 2 j +
1 1 356 4 i + 3 j + 2 1 122 5 i + 4 j + 3 0 1200 6 i + 5 j + 3 1
467 7 i + 6 j + 4 1 502 8 i + 7 j + 5 1 301 9 i + 8 j + 6 0 1200 10
i + 9 j + 6 1 722 11 i + 10 j + 7 1 202 12 i + 11 j + 8 1 392 13 i
+ 12 j + 9 0 1200 14 i + 13 j + 9 1 456 15 i + 14 j + 10 1 188 16 i
+ 15 j + 11 1 376
[0043] In the table above illustrating data packet sizes in bytes
are included, and it is possible to use these packet sizes when
estimating which type of image frame a packet belongs to, since a
data packet with a relatively larger packet size more likely
belongs to an intra coded frame.
[0044] If the sequence of packet sequence number indicates that a
packet has been lost (a sequence gap), the image frame number and
the marker bit of the previous and following packets can be used to
determine to which frame the lost packet belongs. In this example
packet number 9 was lost, and looking at packet 8 and packet 10
both packets have the marker bit set to "1", which means that
packet 8 and 10 are the last packets of their frames. The lost
packet 9 thus belong to image frame number j+6 and by looking at
the number of packets and the aggregated size we can estimate it to
be an intra coded frame.
[0045] The image frame number j of a data packet is calculated by
using the timestamp value of the data packet and by using the coded
frame-rate (picture clock frequency). In more detail:
Image frame
no..sub.SeqNo=1+(TimeStamp.sub.SeqNo-StartTime)/frameTime,
where frameTime=1/frameRate, one is added since the first frame
sequence number should be 1, and StartTime is the TimeStamp of the
first data packet (StartTime=TimeStamp.sub.1).
[0046] In this example TimeStamp is located in the RTP header for
each data packet and is the time when the packet (or rather the
decoded frame that the packet belong to) should be played in the
media player.
[0047] FrameRate (or picture clock frequency) is the number of
frames per second that the source material is sampled with, and
depends on the used codec.
[0048] As the data packets are distributed over an interval,
distances between data packets may be defined, typically by a
difference in the data packet sequence numbers. Distances between
image frames are defined by the difference between the sequence
numbers of the last data packets of the image frames, while a
distance between a data packet and an image frame is defined by the
data packet sequence number and the sequence number of the last
data packet of the image frame.
[0049] With reference to FIG. 4, the inventive method is
illustrated and comprises a first step 42, which comprises
identification of lost data packets 3, 4, 7, 8, 9 of the video
stream S, which is done by investigating which data packet sequence
numbers are missing, where a missing sequence number means a
missing data packet.
[0050] Next a second step 43 is performed and comprises
identification of intra coded frames I1, I2, I3, I4 of the video
stream S is performed. This is done by comparing data bit-size of
packets belonging to a target image frame with data-bit size of all
packets belonging to image frames surrounding the target image
frame. If the target image frame is more than or equal to x times
larger than the mean of the surrounding frames the target frame is
considered to be an intra coded image frame. A suitable value of x
is for a standard H.264 baseline stream typically 2.5. For a lost
data packet a mean data packet size is used.
[0051] To determine data bit-size of packets belonging to a target
frame, bit-sizes of all packets with same image frame number
(timestamp) belonging to the target frame are added. If a sequence
number is missing a packet is lost. The total size of packets
belonging to a frame then represents the image frame size.
[0052] Thereafter it is in a third step 44 determined which of the
intra coded frames I1, I2, I4 that have a maintained image quality,
which is done by estimating 45 if a lost data packet 9 is
associated with an intra coded frame I3. In further detail, if the
sequence numbers of data packets having the same image frame number
are sequential, no data packet is missing and the frame has a
maintained image quality.
[0053] A fourth step 46 comprises estimation of a distance D1, D2,
D3, D4, D5 between a lost data packet 3, 4, 7, 8, 9 and a next
subsequent intra coded frame I2, I4 having a maintained image
quality is done according to the definition of distances above.
[0054] Finally, in a fifth step 47 quality value Q is generated
based on the distances D1, D2, D3, D4, D5. In its most simple form
the quality value Q is the sum of the distances, which in this
example means that Q may be D1+D2+D3+D4+D5=3+2+7+6+5=23. This is an
objective quality value which may be interpreted by a subjective
evaluation done by users watching the video, such that different
quality values have corresponding different perceived video quality
values.
[0055] The quality value may be calculated by weighting the
distances, for better reflecting the perceived video quality. One
method of weighting includes weighting of a long distance D1 higher
than a shorter distance D2, e.g. by using an exponential formula
such as Q=e.sup.D1+e.sup.D2+ . . . . However, in practice more
advanced exponential formulas may be used. For a better quality
value this kind of weighting is done particularly for distances
that refer to the same intra coded frame having a maintained image
quality.
[0056] The weighting may also include weighting the distance D5
belonging to the intra coded frame I3 higher than the weighting of
the distance D3 belonging to the predicted image frame P3, e.g. by
multiplying the D5 value with a factor y prior the summarization of
distances, or prior to inserting the distance values in the
exponential formula.
[0057] Moreover, the quality value may also depend on the data
packet loss rate which per se is determined in a manner common
within the art. For example, the loss rate may then be multiplied
with the sum of the distances when determining the quality
value.
[0058] Although various embodiments of the invention have been
described and shown, the invention is not restricted thereto, but
may also be embodied in other ways within the scope of the
subject-matter defined in the following claims. In particular, the
invention may be implemented by using other methods for determining
which data packet belongs to which image frame.
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