[Live-devel] RTSP video decoding - packets too small

[Guillaume Ferry]

Hello Ross,

Thanks for your reply.

Le 06/09/2010 20:40, Ross Finlayson a écrit :
>> I'm using liveMedia library to implement an audio / video RTSP receiver.
>> To do so, I have created a minimal MediumSink subclass, in which I do 
>> my decoding stuff (using libav* code).
>>
>> It works really fine with streamed audio, but I can't decode videos 
>> properly.
>> I noticed that the frames I'm receiving have really small sizes (sth 
>> like 2000 bytes), and should be more around 60000 bytes to contain an 
>> 'image'.
>
> You haven't said anything about what RTP payload format (codec) the 
> video is using.  Please post an example of the SDP description 
> returned by the server (in response to the RTSP "DESCRIBE" command).
>

Here's the complete SDP :

******************* SDP message ********************
v=0
o=- 1283760697113531 1 IN IP4 127.0.1.1
s=MPEG-1 or 2 Program Stream, streamed by MultimediaRTSPServer
i=video:f24.mpg
t=0 0
a=tool:LIVE555 Streaming Media v2008.07.24
a=type:broadcast
a=control:*
a=range:npt=0-105.379
a=x-qt-text-nam:MPEG-1 or 2 Program Stream, streamed by MultimediaRTSPServer
a=x-qt-text-inf:video:f24.mpg
m=video 0 RTP/AVP 32
c=IN IP4 0.0.0.0
a=control:track1
m=audio 0 RTP/AVP 14
c=IN IP4 0.0.0.0
a=control:track2

******************* End of SDP  ********************

This video has (on purpose) no audio track, so I can focus on video 
stream only.
Payload of value 32 is an MPEG1 or MPEG2 video, if I refer to FFmpeg RTP 
sources.

The thing is, with frames this small (~2000 bytes), I iterate video 
decoding on it until libavcodec tells me we have a complete frame : it 
seems to work fine with the first frame (I can't display it though), 
afterwards, the video decoder seems completely lost.

Then, I inserted some traces into FileSink.cpp, and just using openRTSP, 
I noticed that frames sizes were identical to mine... And i can read the 
resulting video file perfectly with FFmpeg or VLC.

If you have any more ideas, they are of course welcomed, but liveMedia 
seems not guilty on this one :)

Best regards,
Guillaume.
>
>> PS : some interesting insight : when I try to read one of those 
>> videos with ffplay (small player contained in ffmpeg sources), it 
>> works just fine.
>
> Have you tried using VLC?
Also fine with VLC...

-- 
Guillaume FERRY
Bertin Technologies
Département Bertin Conseil
Activité Traitement de l'Information et du Contenu
/Tél/ 	01.39.30.62.09
/Fax/ 	01.39.30.62.45
/Mail/ 	ferry at bertin.fr
/Web/ 	www.bertin.fr <http://www.bertin.fr>

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