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Streaming Media

Streaming Media. Daniel Johnson. What is it?. What is it?. Playing a media file stored on a remote server on a local client. Examples. iTunes “Shared Libraries” Google Video, youTube, etc. How does it work?. How does it work?. True Streaming Progressive Streaming or Pseudo-streaming.

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Streaming Media

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  1. Streaming Media Daniel Johnson

  2. What is it?

  3. What is it? Playing a media file stored on a remote server on a local client

  4. Examples • iTunes “Shared Libraries” • Google Video, youTube, etc.

  5. How does it work?

  6. How does it work? • True Streaming • Progressive Streaming or Pseudo-streaming

  7. True Streaming • Benefits • Counter piracy • Files stay on the server • No need for DRM • You can start playing anywhere in the file

  8. True Streaming • Costs • Expensive • Requires a “streaming server” • Poor quality • Delay • Jitter • Low resolution

  9. True Streaming • Protocols • RTP – Real-time Transport Protocol • RTCP - Real-time Transport Control Protocol • RTSP – Real-Time Streaming Protocol (All of the above come in a Secure variety) • RDT – Real Data Transport (proprietary – Real Networks) • DAAP – Digital Audio Access Protocol (proprietary – Apple Inc.) • SCTP – Stream Control Transport Protocol

  10. True Streaming - RTP

  11. True Streaming – RTCP “Control” is a bit of a misnomer: • Doesn’t actually control the stream • Used to gather data about the RTP stream • bytes sent • packets sent • lost packets • Jitter • Feedback • Round trip delay • Data can be used by apps to control flow and achieve a better, more consistent stream

  12. True Streaming - RTSP • Similar to HTTP, but with modified/additional commands to facilitate streaming media • Built to be Transport layer independent: • TCP • UDP • SCTP • RTP (most common) • Header is similar to HTTP/1.1

  13. True Streaming - RDT

  14. True Streaming – DAAP • Most widely used true streaming protocol because of the popularity of iTunes • Created by Apple as a proprietary protocol – introduced with iTunes 4 • Reverse engineered and became open source • Apple reasserts ownership with v. 7 • Poorly documented

  15. True Streaming - SCTP • Referred to as “multi-streaming” • Based on the PSTN message delivery concept • Allows multiple source and destination hosts • Keeps much of the reliability of TCP, without the restrictions because it’s basic unit is a full message instead of a byte

  16. True Streaming – SCTP

  17. Progressive Streaming • Benefits • Cheap • Built on existing internet technology • Uses standard web server • No new protocol implementations required • Much better quality (potentially)

  18. Progressive Streaming • Costs • File must be downloaded to client HDD (easy to pirate) • Can’t (technically) navigate file

  19. Progressive Streaming • Uses HTTP (sometimes FTP) to send file to client HDD • Most clients begin playing the file before the get all of it • Speeds up playback • If there’s a problem, playback stops completely • Speed is determined by total size of file • Better quality requires waiting longer, and visa versa

  20. Review True Streaming Progressive Streaming • Expensive – requires a special server • Fast • Controllable • Protected • Cheap – don’t need anything new • Slow(er) • Must start from the beginning • Open

  21. Examples • iTunes “Shared Libraries” • Google Video, youTube, etc.

  22. What about making movies?

  23. Making Movies • The right compression (codecs) • The right resolution

  24. codecs • Not all codecs work for streaming • Streaming codecs should allow • high compression • playback of incomplete files Example: MPEG-1

  25. Optimal Resolution

  26. Brief History – the Stretch • Originally video decoding was done with special hardware based on TV decoding • Rectangular pixels • Cropped the sides • Result was an optimal resolution of 352x240 • Software decoders didn’t bother with this

  27. Brief History – the Stretch The Result

  28. Brief History – the Squish • The other predominant influence on internet video was video conferencing Goals: • conserve bandwidth • Still look good • The result was settling on 176x144 • Most software decoders don’t worry about this either

  29. Brief History – the Squish The Result

  30. Effect of Streaming • Most software decoders ignore the “format” flag in the encoding • A lot of encoders had either the TV format or the video conferencing format as their default resolution (this has mostly been corrected) • Lots of videos made early on were stretched or squished

  31. Conclusion I do not like it on ABC,I do not like it on MTV. I would not, could not on CNN, I would not, could not on ESPN. It can't be 176x144, Bill G. Because then it isn't 4:3!* Use a 4:3 Aspect ratio for you web videos!

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