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DIstorsion on RTP/PCM stream

Posted: 22 Jul 2009 15:24
by mcosta
HI,

I'm developing an application sending, through RTP protocol, audio packets in PCM (8Khz 8bits).
Using VLC I read this stream but the audio has a distorsion.

I used wireshark to ensure that received packets contain correct data. (I tried with a single tone signal).
Can you help me to understand the origin of this distorsion.

Thanks,

Massimo

Re: DIstorsion on RTP/PCM stream

Posted: 22 Jul 2009 18:30
by Rémi Denis-Courmont
Errm, you're using what payload format?

Re: DIstorsion on RTP/PCM stream

Posted: 22 Jul 2009 20:43
by mcosta
The PayloadType is 0 (PCMU).

Packets are transmitted with interval of 20ms.

I'm using the Windows precompiled version of VLC 1.0.0.
I would like to activate some logging features of VLC but I don't know how do this

Thanks

PS. Using SoX, I converted RAW PCM data in Wav and AU file and VLC plays them correctly

Re: DIstorsion on RTP/PCM stream

Posted: 22 Jul 2009 21:14
by Rémi Denis-Courmont
Payload type 0 (PCMU) is monophonic 8000 Hz "µ-law" logarithmic PCM, a.k.a. G.711. If you feed linear PCM samples, then yes, the sound should be distorted.

Re: DIstorsion on RTP/PCM stream

Posted: 23 Jul 2009 10:53
by mcosta
Thank you for the answer. I'll try encoding data.