[FFmpeg-user] Using amerge to convert dual mono to stereo

Tim Nicholson tim.nicholson at bbc.co.uk
Mon Jan 16 09:06:56 CET 2012

On 15/01/12 16:06, Nicolas George wrote:
> Le quartidi 24 nivôse, an CCXX, Tim Nicholson a écrit :
>> Well what I wanted was the first mono stream to be left and the
>> second mono stream to be right. What I got was the first mono stream
>> on both channels.
> Cf. the mail I just posted on -devel: this is not a problem with amerge but
> a problem with -f lavfi being unable to output anything but s16, plus a
> problem with aconvert downmixing everything to mono as a bonus to converting
> to s16.

Yes, quite. I wasn't suggesting it was amerge's fault. Just that in 
order to avoid the unhelpful automatic settings it was necessary to 
force the format.

> You can work around the second problem with aformat=s16:stereo:all at the
> end of the filter chain, but it will need a cleaner solution.

I tried at the beginning of the filter in case I ended up trying to 
force stereo out of an already converted back to mono, but I guess 
either approach will do if that doesn't happen.

I used aconvert in preference to aformat as I'm still not  100% sure of 
its correct use, and I find the current docs a tad confusing....


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