[vlc-devel] Re: Transcode stereo stream to mono AMR

[Herman Meerlo]

Alex Antropoff wrote:
> On Fri, Jan 19, 2007 at 02:34:12PM +0100, Herman Meerlo wrote:
> HM>  Hi,
> HM> 
> HM>  I am trying to transcode a public stereo stream to mobile format using the 
> HM>  AMR audio codec (and H.263 for video). This gives no problem if the input 
> HM>  source is mono because AMR is mono as well. But when the input source is 
> HM>  stereo (or more) then the transcode fails.
> HM>  The problem has been around for a long time and I was wondering whether 
> HM>  there is a workaround for this? Can someone maybe explain what is going 
> HM>  wrong so I can try to make a patch mysel. I would think that it can not be 
> HM>  very hard to transcode the input to mono. Or am I missing something?
> HM> 
>
> HM>  [00000616] linear_resampler private debug: fl32/44100KHz/2->s16l/8000KHz/1
> HM>  [00000616] main private debug: using audio filter2 module "linear_resampler"
> HM>  [00000617] main private debug: looking for audio filter2 module: 5 
> HM>  candidates
> HM>  [00000617] audio_format private debug: fl32->s16l, bits per sample: 32
> HM>  [00000617] main private debug: using audio filter2 module "audio_format"
> HM>  [00000618] main private debug: looking for audio filter2 module: 5 
> HM>  candidates
> HM>  [00000614] main encoder debug: removing module "ffmpeg"
> HM>  [00000581] stream_out_transcode private debug: number of audio channels for 
> HM>  mixing changed, trying to reopen the encoder for mixing 2 to 2 channels
> HM>  [00000614] main encoder debug: looking for encoder module: 7 candidates
> HM>  [00000614] ffmpeg encoder debug: libavcodec already initialized
> HM>  [00000614] ffmpeg encoder warning: Only mono supported
> HM>  (amr_nb at 0x82c56d0)
> HM>  [00000614] ffmpeg encoder error: cannot open encoder
> HM>  [00000581] stream_out_transcode private error: cannot find encoder ((null))
> HM> 
> Anyone has solved this problem ?
> Currently I have to use afilter=mono and --sout-mono-downmix with vlc 0.9.0,
> with 0.8.6 all work fine.  
>
>   
Hi Alex,

I did not manage to get this working and therefore had to settle for a 
stereo stream. Jean-Paul has confirmed in this thread that this is a 
kind of fundamental problem in the way VLC is designed to handle 
transcoding. Please see the post of me on Jan-24-2007 and the reply from 
Jean-Paul on Feb-27-2007.

Regards,
Herman

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