Samara State Aerospace University, 2011

Transcription

1 E.S. Sagatov, A.M. Sukhov Samara State Aerospace University Moskovskoe sh. 34, Samara, , Russia 1 Samara State Aerospace University, 2011

2 Beginning points 2 High degradation levels due to packet losses and delay variations (network jitter) in wireless networks. Adaptation of modern coding algorithms for transfer of video frames over wireless networks such as 3G, Wi-Fi and WiMAX. The goal is to create a mathematical method for predicting the quality of video on the user side on the characteristics of the wireless network.

3 Score methods of the video quality 3 The method of subjective score (Mean Opinion Score, MOS) Subjective Assessment Method for Video Quality evaluation ( SAMVIQ ) [1] [2]. The expert is a group of people. The method of objective score evaluation is conducted with the special software, by-frame comparison. GAP Good, Acceptable and Poor gradation levels [3] [4]. [1] EBU BPN 056: SAMVIQ Subjective Assessment Methodology for Video Quality Report by EBU Project Group B/VIM (Video In Multimedia), May [2] SAMVIQ A New EBU Methodology for Video Quality Evaluations in Multimedia F. Kozamernik, V. Steinman, P. Sunna, E. Wyckens, IBC 2004, Amsterdam, pp [3] Calyam, P., Sridharan, M., et al.: Performance Measurement and Analysis of H.323 Traffic, PAM Workshop, [4] Claypool, M., Tanner, J.: The Effects of Jitter on the Perceptual Quality of Video, ACM Multimedia, 1999.

4 Analytical model 4 Q mos = Q ideal αp βj Q ideal p j Q mos α, β the highest quality of video for the codec, the scores from one to five percentage of packet loss, % variation of packet delay (network jitter) at the time of error, ms video quality at the receiving side, the scores of one to five coefficients of the model, which can be found experimentally

5 The role of key frames 5 I P P P P I P P P P I P P P I key frame P not key frame Bears in itself the full information on the video image and it can be restored without reinforcement with the additional data In the stream is ~7% Codes difference between the previous and current frames In the stream is ~93%

6 Plan of experiments

7 The information about video files 7 Tested codecs MPEG-4 (DivX ) MPEG-2 Windows Media Video 9 Coding Options video resolution 320 x 240 framerate 24 fps bitrate 256 Kbps encoding quality maximum

8 8 Search distorted frames

9 9 Journal of network packets

10 10 Errors in the sequence of RTP packets

11 The coefficients of the model 11 Model Q mos = Q ideal αp βj Codec Q ideal α k β k α w β w Wi-Fi 3G 1 MPEG-2 4,2±0,2 0,11±0,03 15±4 0,06±0,02 10±4 2 MPEG-4 4,7±0,2 0,25±0,05 15±5 0,17±0,02 10±3 3 WMV9 4,7±0,2 0,25±0,11 20±8 0,16±0,6 10±3 Codec Q ideal α k β k α w Β w 1 MPEG-2 4,2±0,2 0,12±0,02 10±2 0,06±0,01 5±1 2 MPEG-4 4,7±0,2 0,22±0,05 13±5 0,12±0,05 8±3 3 WMV9 4,7±0,2 0,32±0,1 15±5 0,22±0,08 10±3 Codec Q ideal α k β k α w Β w WiMAX 1 MPEG-2 4,2±0,2 0,2±0,1 15±0,5 2 MPEG-4 4,7±0,2 0,5±0,3 30±1 0,3±0,1 15±0,5 3 WMV9 4,7±0,2 0,3±0,1 15±0,5

12 Ways to improve the quality of video 12 The video player on the receiver side should selectively discard duplicated RTP packets The server of streaming video should duplicate the packets containing the information of key frames The period between key frames can t exceed 2 seconds (optimally 1 second) to avoid video quality degradation

13 Duplicating key frames 13 An example of standard RTP streams (VVoIP) I B B P B B P B B I B B P B B P B B Example of a modified RTP stream (VVoIP) duplicate I-frame duplicate I-frame I I B B P B B P B B I I B B P B B P B B I intra-coded frames Bears in itself the full information on the video image and it can be restored without reinforcement with the additional data In the stream is ~7% P B predictive-coded frames bidirectionally-predictivecoded frames Bears in itself the information about the changes between the current frame and one or two previous or subsequent I-or P-frames In the stream is ~93%

14 MPEG-4 key frame indicator 14 Typically, the packet type is IP Packet identificator and source address need for dropping duplicated packets Typically, the protocol is UDP Required header of RTP packet MPEG-4 video stream indicator MPEG-4 key frame indicator in video stream... Audio, Video, Synchronization and other payloads

15 MPEG-2 key frame indicator 15 Typically, the packet type is IP Packet identificator and source address need for dropping duplicated packets Typically, the protocol is UDP Required header of RTP packet MPEG-2 video stream indicator Audio, Video, Synchronization and other payloads MPEG-2 key frame indicator in video stream

16 WMV9 key frame indicator 16 Typically, the packet type is IP Packet identificator and source address need for dropping duplicated packets Typically, the protocol is UDP Required header of RTP packet WMV9 video stream indicator Audio, Video, Synchronization and other payloads WMV9 key frame indicator in video stream. The 17th byte of PES data.

17 17 Plan of the experiment with duplicating packets

18 Tool development 18 Windows network drivers hierarchy In the process of testing ideas to improve the video quality we have developed tools that 1) drop duplicate packets at the receiving end; 2) can duplicate packets that contain all the video frames or key frames only.

19 Effect of packet duplication 19 Q in Wi-Fi (IEEE802.11b) Codec Without packets duplication With key frames duplication With full packets duplication 1 MPEG-2 0,7 0,3 1,0 2 MPEG-4 1,2 0,4 1,5 3 WMV9 1,2 0,4 1,5

20 Thank you for your attention 20 All network logs, as well as video streams obtained during the experiments, you will find on the Internet at: To contact the author use the address : sagatov@ya.ru