[FFmpeg-devel] Trouble with GSM audio.

[Artem Korneev]

Michel Bardiaux wrote:
> Artem Korneev a ?crit :
>   
>> Last weeks I spent in attempting to decode audio frames from GSM format 
>>     
>
> There aint no such animal. You probably mean GSM *codec*, in a wav, right?
>   
Hmm.. I have a frames, which comes from the network. And I know, that 
these frames contains audio in GSM.

>> to PCM. But I still have no solution. :(
>>
>> I've initialize codec context by these lines:
>>
>>     inCtx->bit_rate       = 13000;
>>     inCtx->sample_rate    = 8000;
>>     inCtx->channels       = 1;
>>
>> and after that, decode buffer with GSM audio by this code:
>>
>>     while ( in_size > 0 ) {
>>         outbuf_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
>>         decoded_len = avcodec_decode_audio2(inCtx, samples_ptr, 
>> &outbuf_size, inbuf_ptr, in_size);
>>
>>         in_size     -= decoded_len;
>>         inbuf_ptr   += decoded_len;
>>         samples_ptr += outbuf_size;
>>     }
>>
>> ..and only noise I have as result. :( Does anybody have a workable 
>> example of code for decoding GSM?
>>     
> Yes: ffmpeg.c!
>   
This source use decoding from the file, as I know. But I need to use it 
with the buffer, which contains frame.
> Please try ffmpeg -i on your input.
>   
I have no input files, so I tried this command with the dump (I save all 
incoming frames into the dump file):

% ffmpeg -i 
dumpgsm1.gsm                                                                                          
/tmp
FFmpeg version SVN-rUNKNOWN, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --enable-libfaac --enable-libfaad --enable-libmp3lame 
--enable-libgsm --prefix=/usr/ --disable-ffserver --disable-debug 
--disable-static --enable-shared --enable-pthreads --enable-gpl
  libavutil version: 49.3.0
  libavcodec version: 51.38.0
  libavformat version: 51.10.0
  built on Sep 26 2007 18:41:17, gcc: 4.1.2 20061115 (prerelease) 
(Debian 4.1.1-21)
dumpgsm1.gsm: Unknown format

But when I feed this file to gpe-soundbite (gpe-soundbite play 
dumpgsm1.gsm), I have hear a correctly sound. So, I think, that input is 
correct.
> Chances are, its not GSM but GSM-MS. Is the codec_id right?
>   
May be, but I'm already tried to use CODEC_ID_GSM_MS as well as 
CODEC_ID_GSM. No result yet. :(