[Libav-user] libavformat RTP management

[William MANCON]

I used av_sdp_create to get the correct SDP. this function gave me :
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 53.21.1
m=video 5000 RTP/AVP 96
b=AS:128
a=rtpmap:96 VP8/90000

And after that i tried to write the stream to a file using :

ffmpeg -i sdp.foo  -c:v copy  output.webm -loglevel debug

This is the output :

Applying option loglevel (set logging level) with argument debug.
Successfully parsed a group of options.
Parsing a group of options: input file sdp.foo.
Successfully parsed a group of options.
Opening an input file: sdp.foo.
[sdp @ 0x442a320] Format sdp probed with size=2048 and score=50
[sdp @ 0x442a320] video codec set to: vp8
[udp @ 0x4431780] end receive buffer size reported is 131072
[udp @ 0x4431580] end receive buffer size reported is 131072
[NULL @ 0x4430e20] setting jitter buffer size to 500
[sdp @ 0x442a320] Before avformat_find_stream_info() pos: 143 bytes
read:143 seeks:0
[sdp @ 0x442a320] Received no start marker; dropping frame


It look likes ffmpeg do not read data on the line ?!

After launching the command It seems to wait for something, I wait few
minutes and I do a Ctrl+c

then the output is :

[sdp @ 0x442a320] Could not find codec parameters for stream 0 (Video: vp8,
1 reference frame, yuv420p): unspecified size
Consider increasing the value for the 'analyzeduration' and 'probesize'
options
[sdp @ 0x442a320] After avformat_find_stream_info() pos: 143 bytes read:143
seeks:0 frames:0
sdp.foo: could not find codec parameters
Input #0, sdp, from 'sdp.foo':
  Metadata:
    title           : No Name
  Duration: N/A, bitrate: N/A
    Stream #0:0, 0, 1/90000: Video: vp8, 1 reference frame, yuv420p, 90k
tbr, 90k tbn, 90k tbc
Successfully opened the file.
Parsing a group of options: output file output.webm.
Applying option c:v (codec name) with argument copy.
Successfully parsed a group of options.
Opening an output file: output.webm.
Output #0, webm, to 'output.webm':
Output file #0 does not contain any stream
[AVIOContext @ 0x4432da0] Statistics: 143 bytes read, 0 seeks

I do not understant "sdp.foo: could not find codec parameters"

Someone have an idea of what append ?

If I try with ffplay : ffplay sdp.foo
A windows apprear but the video is a black screen. Nothing else.

Do someone understand what's happening ?

On Fri, Oct 23, 2015 at 3:02 PM, William MANCON <wmancon at gmail.com> wrote:

>
> Just to make sure: On this mailing list, only the
>> libraries from the FFmpeg project are supported.
>>
>
> > Yes,
>
> I suspect the payload descriptor is not added by
>> the encoder function (which is in libavcodec) but
>> by the muxer (in libavformat).
>>
>> You should be able to use ffmpeg (the command line
>> tool) to test.
>>
>> >I tried but  without the correct sdp it fail. I Maybe need to set the
> correct payload type in the code.
> I tried with this sdp :
>
> v=0
> o=- 0 0 IN IP4 127.0.0.1
> s=No Name
> c=IN IP4 127.0.0.1
> t=0 0
> a=tool:libavformat 55.22.100
> m=video 1234 RTP/AVP 96
> b=AS:200
> a=rtpmap:96 VP8/90000
> a=fmtp:96 apt=100
>
> with no luck. the stream is outputted at rtp://127.0.0.1:5000 do i need
> the port to the sdp ?
>
> Thanks Carl for your comment.
>
> William.
> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user
>
>
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