Improve RTSP/RTP layer

Roadmap/checklist for Josh Allmann's Summer of Code Project:

• Primary goal: improve the receiver compatibility
  • Add support for more widespread formats ([list will follow check gst live555 and feng])
    • X-Qt/quicktime depacketizer (see X-QT patch)
    • SVQ3 [1] and QDM2 [2] depacketizers
    • VP8 (see https://groups.google.com/a/webmproject.org/group/webm-discuss/browse_thread/thread/550f946b0e22ead2# )
  • support Quicktime http tunnel mode
    • Initial implementation done and committed, not supported in the RTSP muxer yet
  • untangle the AAC and mpeg4 format specific code from rtsp.c, make them proper dynamic payload handlers
    • Patch submitted, awaiting review
  • factorize out common code for parsing SDP (fmtp) lines, that is duplicated in parse_h264_sdp_line, amr_parse_sdp_line and xiph_parse_sdp_line
  • add RTP packetizers for codecs that we already have depacketizers for (Theora, Vorbis, any other?)
  • support RTCP/Bye as end-of-file (see small task)
• Secondary goal: improve application integration
  • Provide an API to expose the rtcp layer (and the equivalent in RDT dialect)
  • Try to support subtitle streams (either as rtcp-xr or application/text stream)
  • Make VideoLanClient, MPlayer or Xine use FFmpeg RTSP
    • Patch submitted to VLC, awaiting review
  • Implement protocol variations (e.g. DCCP or improve SCTP)

Mentor: Luca Barbato, Martin Storsjö, Ronald S. Bultje