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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM A More Loss-Tolerant RTP Payload Format for MP3 Audio Ross Finlayson LIVE.COM
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Existing RTP payload format for MPEG audio (RFC 2250) Packet boundaries are on MPEG frame boundaries Appropriate for MPEG (1 or 2) layer I or II audio »because their frames are true “application data units” (ADUs) - can be decoded independently Less appropriate for layer III audio (“mp3”) »mp3 frames contain a back-pointer to earlier frames »ADU boundaries don’t correspond to frame boundaries »causes noticeable audio glitches when packets are lost
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Illustration frame ADU
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Illustration frame ADU
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM If a frame gets lost... frame ADU
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM If a frame gets lost... frame ADU Data received, but useless Data lost
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Alternative: Send headers+ADUs, not frames ADU
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM A new RTP payload format for MP3 Identical to the existing format (RFC 2250), except »packets contain complete ADUs - not frames »uses a different payload type (dynamic) Data-preserving rearrangement of the original »no redundancy added => no increase in bit rate However, implementations now need more knowledge of the internals of MP3 frames
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Recent additions to this Internet-Draft How to handle streams with layer I or II frames mixed with layer III »probably an uncommon situation ‘Pseudo-code’ for converting between regular “MP3 frames” and “ADU frames”
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IETF Washington DC, 1999.11Ross Finlayson, LIVE.COM Notes For more information - including audio illustrations: »http://www.live.com/rtp-mp3/ Some multicast MP3 server and receiver tools that (optionally) use this payload format: »http://www.live.com/liveCaster/ Let’s have some more implementations!
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