Backwards compatible adaptive error resilience techniques for MPEG-4 over mobile networks.
Advances in wireless technology will soon provide sufficient capacity for the transmission
of compressed video to and from mobile terminals. However, high compression
ratios and the use of Variable Length Coding in standards such as H.263 and MPEG-4
make the encoded bitstreams particularly sensitive to errors.
This thesis investigates methods for the error robust transmission of MPEG-4 coded
video over mobile networks. It examines curent and future mobile networks, and
discusses the quality of service that they are expected to offer with respect to mobile
multimedia. Also, the MPEG-4 systems and visual layer standards are briefly described.
Real-time MPEG-4 encoder and decoder software has been developed and exploited
in the work described here. The MPEG-4 software can send MPEG-4 data over TCP
or over RTP. All of the standard MPEG•4 error resilience options are implemented in
the software. The effectiveness of these options is demonstrated through the results of
simulated transmission over a GPRS channel.
MPEG•4 is separated into two different streams via exploitation of the data partitioning
option. The two streams may then be transmitted over a mobile network using different
bearer channels. The most sensitive data stream is sent using a bearer channel with a
low bit error rate compared to the less sensitive data stream. This technique is shown
to produce quality improvements.
A technique for the insertion of user-defined data is outlined. Insertion of user- defined
data is achieved while retaining backwards compatibility with existing standard MPEG-
4 decoders. CRC codes are inserted using this scheme, to facilitate more accurate
detection of errors. This error detection aids error concealment and results in a gain in
decoded video quality after simulated transmission over a GPRS channel.
Motion adaptive encoding is employed to increase the error robustness of the encoded
bitstream. Video packet size and Intra block refresh rates are altered with first partition
size, which is used as a guide to the amount of motion within a scene.
1Tansmlssion of video using RTP is considered. In particular, a mathematical analysis
is performed for two different packetisation schemes. One scheme encapsulates one
video frame within one RTP packet, while the other scheme encapsulates a single video
packet within a single RTP packet.