[Ffmpeg-devel] MP3 decoding from RTP stream. Getting "invalid new backstep"

Måns Rullgård mru
Tue Oct 31 10:52:51 CET 2006

Martin Thielen said:
>>>I'm using ffmpeg to encode MP3 data transmit it over RTP and decode it.
>>>If I start the RTP sender before the receiver I get warnings on the
>>>decoder side from the ffmpeg library (only at the very beginning):
>>>backstep:452, lastbuf:0
>>>invalid new backstep 381
>>>overread, skip -5 enddists: -4 -4
>>>overread, skip -9 enddists: -1 -1
>>>invalid new backstep 382
>>>The sound is distorted as well (just for 1 second or so). Is it somehow
>>>possible to tell the AVParser or the decoder to discard the frames that
>>>leads to the distortion?
>> yes if you implement it and send a patch, and yes i fully agree that the
>> mp3 decoder should discard such packets instead of annoying the user
>> with the noise
>> just look at the code which outputs the error messages and silence the
>> output somehowm shouldnt be too hard
>> [...]
> Hi,
> I'm trying to silence the distorted output now. What would you consider

Didn't Michael already do something?

> the best way:
> 1) Return a value that indicates a problem
> 2) Set a flag (which one?) in AVCodecContext that indicates a problem
> 3) Changing the buffer values to 0? Is 0 the right value for silence?

Zero is not a good value as it will cause pops or clicks if the previous
sample has a large value.

M?ns Rullg?rd
mru at inprovide.com

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