Chapter 4 Experimental Results
4.2 On-Line Testing
With the on-line evaluation on the multimedia test bed, the simulations of video content delivery with the proposed robust system without use of motion information over wireless channels are shown in Fig. 46 and Fig. 47. We test each case with different combinations of a retransmission scheme and Resync_Markers to evaluate the visual quality of the reconstructed video sequences. Tool 1 disables simultaneously the retransmission scheme of the test bed and the use of Resync_Marker in the coded bitstream. Tool 2 adopts the same techniques as in the Tool 1 except the use of Resync_Markers. Tool 3 enables both tools at the same time, which can have the best subjective quality on the average for streaming video contents over the wireless channels. The simulation results show that the Tool 3 has the best visual quality.
As observed from the reconstructed video frames, the proposed video streaming system can provide better subjective visual quality of receiving videos for the consumers.
(a) (a)
(b) (b)
(c) (c) Fig. 46. The visual quality comparisons for
the 3 combinations of the tools within the error resilience system. (a) Tool 1; (b) Tool 2; (c) Tool 3.
Fig. 47. The visual quality comparisons for the 3 combinations of the tools within the error resilience system (a) Tool 1; (b) Tool 2;
(c) Tool 3.
As the packet loss rate increase, retransmission can reduce the packet loss rate of transmission channel. Deciding which packet should be retransmitted first or using efficient retransmission can make the results better. Besides, network bandwidth is also an impact factor affecting the retransmission performance. With enough bandwidth to retransmit all the packets, we could make the decoder to get the error free bitstream.
4.3 Summary
The experiment results show that the proposed error concealment method and error resilience system can improve the video quality under the packet loss through transmission channels. In addition, intra refreshment in the encoder for off-line testing or retransmission scheme in the system for on-line testing is also taken into consideration. By combining the motion concealment, intra refreshment and retransmission, the error resilient and crash proof decoder can improve the visual quality of received video significantly.
Chapter 5 Conclusion
5.1 Contributions
This thesis has developed an efficient error concealment and error resilient MPEG-4 decoding system.
1. For any packet loss that causes the loss of MBs or VOP headers during the transmission, we have proposed an error resilient decoding system that can prevent the decoder from being crashed, provide a reconstructed video of proper visual quality, and retain the temporal resolution.
2. For the corrupted MBs, we have proposed an adaptive block-based hybrid error concealment method. The innovations are the hybrid concealment scheme with less complexity, block-based concealment to refine MB-based method, and a smooth filter is used to make the concealment results have better visual quality. Based on our proposed method, the damaged video can recover the quality and provide a good performance both on PSNR and visual quality.
3. The error resilient decoding system is simulated on the MPEG-21 part-12 multimedia test bed under various network conditions. The simulation results show that the error resilient decoding system is applicable to video communications or video streaming.
5.2 Future Works
For the multimedia including text, audio, and video, error resilience only on video coding is not sufficient to provide a good media service. Different kinds of media all need to be investigated. For the streaming system, decoder is combined with client. Taking client and network conditions into consideration, we may have more information and ability to get best
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自 傳
黃名彥: 民國 1980 年生於高雄市。 2002 畢業於台灣新竹的國立交通大學 電子工程學系，之後進入該校電子工程所攻讀碩士學位。以 MPEG-4 解碼 器為論文研究主題。
Ming-Yen Huang was born in KaoHsiung in 1980. He received the BS degree in Electronics Engineering, National Chiao Tung University (NCTU), HsinChu, Taiwan in 2002. His current research interest is MPEG-4 decoder.