Sudarsun S 1 Audio and Video over Internet Sudarsun S., M.Tech Checktronix India Pvt Ltd Chennai

Sudarsun S 2 Introduction What is Audio/Video over Internet? What are the benefits of AV on Internet? –Cost of traditional communication –Availability/Mobility with Wireless –Entertainment Industry On demand Movie, Songs Duplication Protection –Distance does not matter! –Decentralization What is and Why Streaming data? Real-time Communication Protocols

Sudarsun S 3 Agenda Learn the fundamentals of streaming –TCP, UDP and their limitations –RTP, RTSP to overcome TCP limitations –Error Correction and Detection Low Quality Piggybacking Interleaving Understand “On demand” multimedia data –On demand cinema Video conferencing

Sudarsun S 4 Overview The big picture

Sudarsun S 5 Media Data types Audio : WAV, MP3, RM Video: AVI, MPG, MOV, RM Bandwidth calculation 3GPP, 3GPP2 –3rd generation, high-speed wireless networks MPEG4 –Professional-quality audio and video streams H264 formats –MPEG-4 standard (Part 10) used across 3G for mobile devices to iChat AV for video conferencing to HD for broadcast and DVD

Sudarsun S 6 TCP & UDP Connection Oriented – Is that a Overhead ? Connectionless – Will that guarantee timely delivery? Maximum Effort Reliability vs Just In Time with permissible error rate Packet Sequence – Is that an Advantage ? Summary of general deficiencies

Sudarsun S 7 RTP (RFC 3550) Real-time Transport Protocol on UDP Uses RTCP (special set of messages) to exchange periodic reports One RTP session per media flow 16 bit sequence numbers to detect packet loss 32 bit time stamp to handle jitter due to network

Sudarsun S 8 RTP Format (V) Version; 2 bits(P) Padding; 1 bit. (X) Extension; 1 bit.(CC) CSRC Count; 4 bits. (M) Marker; 1 bit.(PT) Payload Type; 7 bits. Sequence Number; 16 bits.Time Stamp; 32 bits. SyncSRCId; 32 bits.ContributingSRCId List;

Sudarsun S 9 How RTP Works? IP UDP RTP HDR Audio Payload IP UDP RTP HDR Video Payload Uses separate sessions for audio and video Uses sequence number to synchronize audio/video

Sudarsun S 10 RTP Vs OSI PCMA audioMPEG2 videoApplication RTP Transport UDP IP Network EthernetFrame RelayData Link

Sudarsun S 11 RTCP Supervise QoS Reception reports, Sender reports, Source description Reports: packets sent/lost, inter-arrival jitter Helps modify sender transmission rate and for diagnostics purpose RTCP bandwidth = 5% of session BW Commands: SR, RR, SrcDESc, BYE, APP

Sudarsun S 12 Continuous Media Real-time (Video Conferences) –Interactive –Tight timing relationship –Error rate/Jitter to be near Zero Streaming –Playback stored media –Error rate need not be very low –Loose timing relationship

Sudarsun S 13 RTSP (RFC 2326) Application-level protocol for control over the delivery of data with real-time properties. Works on top of HTTP Extensible framework to enable controlled, on- demand delivery of real-time data. Supports live data feeds and stored clips Controls multiple data delivery sessions (UDP, multicast UDP, TCP). Delivery mechanisms based on RTP.

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Sudarsun S 15 RTSP Methods OPTIONS- obtain available methods SETUP- Establish transport ANNOUNCE- alter description of media object. DESCRIBE- get low level description of media object. PLAY- start playback. RECORD- Start recording PAUSE- suspend delivery, keep state SET_PARAMETER- device or encoding control TEARDOWN- remove state.

Sudarsun S 16 Error Correction Piggy backing (FEC) Interleaving Combine both

Sudarsun S 17 Low Quality Piggybacking Works for single packet loss, How about multi-packet loss ?

Sudarsun S 18 Interleaving Data blackout is recovered with intermittent jitter

Sudarsun S 19 Network Strategies Multicasting reduces amount of redundant data transferred Streaming media delivery networks allow for multiple, geographically scattered servers (achieved either by splitting or caching) Dedicated networks guarantee bandwidth Multiple-access transmissions over Internet— requested info sent from several different locations simultaneously

Sudarsun S 20 Streaming Media Three modes in which video information can be streamed: –Live broadcasting –On-demand streaming –Conferencing

Sudarsun S 21 Live Broadcasting System SLTA: Simulated Live Transfer Agent (Rebroadcasting)

Sudarsun S 22 On-demand System Structure

Sudarsun S 23 Streaming Media – On demand Distribution system similar to live broadcasting system, except: –No direct connection between encoder and server –Remote proxy servers can cache popular files –Clients allowed to rewind, fast forward, etc. –Server proxy transfers only initiated by client

Sudarsun S 24 Where to Get More Information html html streaming.html streaming.html uide.htm uide.htm lVideoStreaming.html lVideoStreaming.html

Sudarsun S 25 Limitations Bandwidth limitation Congestion and Quality of network Buffer Overhead in Portable devices Compression and Decompression overhead Security issues –Eavesdropping –Duplication by Data Augmentation

Sudarsun S 26 Some Servers Audio –Winamp’s Shoutcast Server –Streamsicle Broadcast server –RealMedia Stream server Video –Quicktime Server –Helix universal server –Macromedia communication server –Ffmpeg (

Sudarsun S 27 Conclusion Streaming multimedia poses many challenges to video encoders –Variability of channel performance –High server workloads Need to adapt coded bit rate to match channel capacities; must be done efficiently and on the fly

Sudarsun S 28 Thank You Sudarsun S., M.Tech Director – Research and Development Checktronix India Pvt Ltd November 2005