[vlc-devel] FYI: New LIVE555 support for receiving Vorbis audio and VP8 video RTP streams

[Ross Finlayson]

FYI, the latest version (2011.11.08) of the "LIVE555 Streaming Media" libraries supports receiving Vorbis audio and VP8 video over RTP, and so, such streams could now be played by VLC relatively easily.

Updating the "live555.cpp" interface code to support VP8 video RTP streams should be straightforward: Just test for the codec name "VP8".

Updating the code to support Vorbis audio RTP streams is not quite as trivial, because decoding Vorbis requires first passing to the decoder 'configuration' information, which is carried 'out of band' in the stream's SDP description.

This configuration information is accessed - as a string - by calling "sub->fmtp_config()", as you do elsewhere in the code for some other codecs.   For Vorbis, this string is a Base64-encoded string.  If you Base64-decode it (using the LIVE555 "base64Decode()" function, if you wish), you will end up with a block of "packed headers" data, as described by Figure 6 and Figure 7 (Section 3.2.1) in RFC 5215.

The Vorbis decoder might also require the stream's "Ident" field - a 24-bit value that can be used to index the particular configuration currently being used by the stream.  This field - if needed - can be obtained by calling "VorbisAudioRTPSource::curPacketIdent()".  (This returns a 32-bit value; the low-order 24 bits form the "Ident" field.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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