[FFmpeg-user] Problems parsing SDP file for RTP type 33

[Ben Barker]

Hi,

I have two SDP files. On points to an Mpeg4 multicast stream, the
other to a Mpeg 2 DVB stream.

If I try to access the former with the following sdp:

v=0
m=video <port> RTP/AVP 96
c=IN IP4 <mcaddress>
a=rtpmap:96 MP4V-ES/90000
a=source-filter: incl IN IP4 <mcaddress>  <source_address>

All works fine, and from the command line I see that the SDP has been
properly parsed:

FFmpeg version git-b319052, Copyright (c) 2000-2011 the FFmpeg developers
  built on Aug 15 2011 16:42:18 with gcc 4.1.2 20070626 (Red Hat 4.1.2-14)
  configuration:
  libavutil    50. 37. 0 / 50. 37. 0
  libavcore     0. 16. 1 /  0. 16. 1
  libavcodec   52.109. 0 / 52.109. 0
  libavformat  52. 97. 0 / 52. 97. 0
  libavdevice  52.  2. 3 / 52.  2. 3
  libavfilter   1. 74. 0 /  1. 74. 0
  libswscale    0. 12. 0 /  0. 12. 0
found ssm_source..<source_address>
found ssm_source....<source_address>

At which point streaming starts.

If however I try to access my Mpeg2 stream using the following sdp:

v=0
m=video <port> RTP/AVP 33
c=IN IP4 <multicast_address>
a=rtpmap:96 MP4V-ES/90000
a=source-filter: incl IN IP4 <multicast_address> <source_address>

Then ffmpeg returns:


FFmpeg version git-b319052, Copyright (c) 2000-2011 the FFmpeg developers
  built on Aug 15 2011 16:42:18 with gcc 4.1.2 20070626 (Red Hat 4.1.2-14)
  configuration:
  libavutil    50. 37. 0 / 50. 37. 0
  libavcore     0. 16. 1 /  0. 16. 1
  libavcodec   52.109. 0 / 52.109. 0
  libavformat  52. 97. 0 / 52. 97. 0
  libavdevice  52.  2. 3 / 52.  2. 3
  libavfilter   1. 74. 0 /  1. 74. 0
  libswscale    0. 12. 0 /  0. 12. 0
found ssm_source..|2ÿ½
udp_resolve_host: Temporary failure in name resolution
found ssm_source..|2ÿ½

Here you can see that the ssm given above is not that in the SDP - not
even a valid IP address. After a few trials, the key thing that causes
this to happen seems to be changing the RTP type in the sdp file from
96 to 33.

Can anyone suggest why this is failing? Both SDP files have been
tested and ar working if passed into VLC from the same machine...