Effects of P2P Streaming on Video Quality

1. Effects of P2P Streaming on Video Quality Csaba Kiraly, Luca Abeni, Renato Lo Cigno DISI – University of Trento, Italy kiraly@disi.unitn.it

2. Problem domain P2P Streaming, also known as P2P-TV • Examples you might know • PPLive, SoapCast, TVAnts, etc. • How they work? • A source generates encoded audio/video • This media stream is divided into chunks • Various peers receive the encoded media and contribute to the diffusion, by forwarding received chunks to other peers • Live stream, so delay does matter! ICC 2010, Cape Town, 23-27 May 2010

3. Studying chunk diffusion • Numerous simulators are available to study these systems • P2PTVSim, PeerSim, SSSim, etc. • These provide answers like 0.8 Mb/s with 4% chunk loss ↔ 0.7 Mb/s with 2% loss ICC 2010, Cape Town, 23-27 May 2010

4. Our Contribution • Methodology and tools for the comparison of P2P-TV systems through the evaluation of received video quality • As seen by the user • Simulation driven by real video traces • Instead of simplifying assumptions, like “… lets assume the video is 1Mb/s CBR …” • Initial evaluation using the new tool • Choice of encoding rate • Confronting chunkization schemes • Various codecs ICC 2010, Cape Town, 23-27 May 2010

5. Methodology and Tools overlay topology chunk rate and sizechunk and peer schedulers Raw video stream • Codec • Encoding rate • GOP size • etc. Encoder Chunkizer chunk time and size trace • Chunk forming: • fixed size • 1 chunk = 1 GOP • 1 chunk = N frames P2P Simulator chunks chunk loss Remove lost chunks corrupted stream • Use codec’s error concealment • replicate last decoded frame Fill missing frames refilled stream Compare PSNR, SSIM, etc. ICC 2010, Cape Town, 23-27 May 2010

6. Simulation parameters • 1000 peers • Push based operation based on buffer map of neighbours • Overlay • unstructured • random regular graph overlay with degree 20 • Network • Access link constrained • Homogeneous upload bandwidth of 1 Mb/s • Download bandwidth is not a bottleneck • Raw stream: “foreman” sequence looped 4 times • Encoding: H.264 using ffmpeg and x264 ICC 2010, Cape Town, 23-27 May 2010

7. Streaming rate vs. chunk loss • Curves became flat: • Quality gained by increased encoding rate is lost during transmission ICC 2010, Cape Town, 23-27 May 2010

8. Blind vs. media-aware chunkization • Comparing chunk creation policies • Blind: each chunk has same fix size, independent of stream structure • Media-aware: respect frame boundaries, e.g.1 chunk = 1 GOP (Group Of Pictures) ICC 2010, Cape Town, 23-27 May 2010

9. The effect of schedulers Comparing different chunk and peer selection policies • a good scheduler • ensures lossless delivery with low delay • Guarantees unaffected PSNR to the users. ICC 2010, Cape Town, 23-27 May 2010

10. Choosing the right codec • Evaluated received video quality as a function of video rate with 4 codecs • No real surprises • H.263 < MPEG2 < MPEG4 < H.264 • Slight differences in the optimal working point • Because of different error concealment implementations ICC 2010, Cape Town, 23-27 May 2010

11. Conclusions • Simulating the P2P system and evaluating the quality of video “as seen by users” is feasible • The proposed methodology allows joint evaluation of media encoding, chunkization strategies, and “traditional” peer parameters, such as scheduling and overlay algorithms • Tool-chain available as open source GPL code: http://napa-wine.eu Questions? ICC 2010, Cape Town, 23-27 May 2010