[FFmpeg-trac] #5266(ffmpeg:new): Incorrect sdp file format and rtp timestamps when sending multicast streams

[FFmpeg]

#5266: Incorrect sdp file format and rtp timestamps when sending multicast streams
-------------------------------------+-------------------------------------
             Reporter:  sampsa       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  git-
             Keywords:  rtp          |  master
  timestamp multicast                |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Hello,

 This bug has been tested with ffmpeg version "2.7.6-0ubuntu0.15.10.1" and
 also with the latest "N-78646-g10fa50c" version from the repository.

 I send audio from my local alsa device to a multicast address with the
 command (1):

 {{{
 ffmpeg -y -f alsa -i default -f mulaw -ar 8k -ac 1 -f rtp
 rtp://224.168.1.33:50300 > test.sdp
 }}}

 Now I can try to read that .sdp file with (2) ffplay:

 {{{
 ffplay test.sdp
 }}}

 .. or with some other media player, in this case, with vlc (3):

 {{{
 vlc --aout alsa --alsa-audio-channels 1 test.sdp
 }}}

 Case (2) works fine, but (3) fails.  We can take a look at file
 "test.sdp":

 {{{
 SDP:
 v=0
 o=- 0 0 IN IP4 127.0.0.1
 s=No Name
 c=IN IP4 224.168.1.33
 t=0 0
 a=tool:libavformat 56.36.100
 m=audio 50300 RTP/AVP 0
 b=AS:64
 }}}

 I think the format is wrong here: the first line saying "SDP:" shouldn't
 be there and it drives vlc crazy.

 So, we can fix the file and remove the first line.  Now we have a file,
 lets call it "fixedtest.sdp":

 {{{
 v=0
 o=- 0 0 IN IP4 127.0.0.1
 s=No Name
 c=IN IP4 224.168.1.33
 t=0 0
 a=tool:libavformat 56.36.100
 m=audio 50300 RTP/AVP 0
 b=AS:64
 }}}

 With the fixed sdp file, case (3) works, but only for a while.  Eventually
 vlc tells us that:

 {{{
 [00007f10a4c1de58] core decoder error: Could not convert timestamp 0
 }}}

 I have also seen this:

 {{{
 [00007faeb0c1dbd8] core decoder error: Could not convert timestamp
 2777164513959325
 }}}

 If we launch vlc with the verbose flag, i.e. with:

 {{{
 vlc -vvv --aout alsa --alsa-audio-channels 1 fixedtest.sdp
 }}}

 we see that it goes for forever into a buffering state:

 {{{
 [00007fb56c0009b8] core input debug: Buffering 0%
 }}}

 So, there seems to be one or two bugs here:

 a) incorrect sdp file format (with an extra line)
 b) maybe incorrect timestamps when sending streams with rtp packetization

 If (b) is not a bug, but a vlc problem, please let me know and I'll file a
 bug report at vlc.


 Regards,

 Sampsa

--
Ticket URL: <https://trac.ffmpeg.org/ticket/5266>
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