My PhD Project
My project was entitled Backwards Compatible Adaptive Error Resilience Techniques for Video over Mobile Networks. Its basic aim was to improve the robustness of MPEG-4 to the kind of channel errors present in mobile links. I passed my viva exam on 15 October 2001.
Initial tests corrupting MPEG-4 video with errors showed a number of things:
- Shape coding dramatically increases the sensitivity of MPEG-4 to error.
- The error resilience tools are reasonably effective.
Real-time Video
As part of the ACTS ACCORD project, a real-time MPEG-4 application has been developed to run under Microsoft Windows. This allows raw YUV video data to be encoded, sent over an IP link and decoded in real-time. RTP is used to ensure that transmission delay is minimised, packets are decoded in the correct order, and QoS information is available to the encoder. This software can be used in conjunction with a real-time GPRS emulator that has been developed within the group. At the IEE 3G 2000 conference, a paper detailing some of our real-time video work over GPRS was presented. However, delay times in real GPRS networks are likely to mean that real-time video over GPRS will not be possible. In fact, even streaming video will prove challenging.
Software
The software used for this project has been adapted from source code from MoMuSys, and Microsoft. The original source code is available here (this is the original freely distributable source code without any of the modifications made within CCSR):
Please note that the compiled decoders crash when they encounter errors. They are for demonstrating the MPEG-4 codec, rather than for practical use.
Example Video
The two video sequences featured here show a sequence corrupted with a BER of 10-4. Note that both sequences have been re-encoded to allow them to be downloaded (you will need Windows Media Player to view them).
Novel Achievements
A certain amount of original work has been performed as part of my PhD:
- Prioritisation of MPEG-4 streams over mobile networks
- Backwards compatible insertion of user defined data into MPEG-4
- Motion adaptive error resilient encoding
- Optimimal packetisation study for MPEG-4 over RTP