[FFmpeg-devel] [PATCH] ffmpeg: add -map_channel option.

[Michael Niedermayer]

On Tue, Oct 25, 2011 at 04:29:28PM +0200, Clément Bœsch wrote:
> On Tue, Oct 25, 2011 at 03:28:36PM +0200, Clément Bœsch wrote:
> > On Tue, Oct 25, 2011 at 03:22:12PM +0200, Clément Bœsch wrote:
> > > On Tue, Oct 25, 2011 at 02:25:53PM +0200, Michael Niedermayer wrote:
> > > > On Tue, Oct 25, 2011 at 11:07:53AM +0200, Clément Bœsch wrote:
> > > > > On Mon, Oct 24, 2011 at 06:29:10PM +0200, Michael Niedermayer wrote:
> > > > > > On Mon, Oct 24, 2011 at 04:19:10PM +0200, Michael Niedermayer wrote:
> > > > > > > On Mon, Oct 24, 2011 at 02:05:55PM +0200, Clément Bœsch wrote:
> > > > > > > > On Wed, Oct 19, 2011 at 11:42:15PM +0200, Michael Niedermayer wrote:
> > > > > [...]
> > > > > > > > > also shouldnt rematrix be independant of the existence of a channel_map
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Well, AFAIU, the rematrix is meant to automatically set the audio gain
> > > > > > > > levels for each channel; the channel mapping is "incompatible" with this,
> > > > > > > > it's all about reordering, or maybe with another phrasing: ppl won't
> > > > > > > > expect the levels to change (the number of output channels being fixed by
> > > > > > > > the number of -map_channel and not a specific -ac option)
> > > > > > > 
> > > > > > > if your inputs represents 5.1 and your output represenst 7.0 you need
> > > > > > > the rematrix code
> > > > > > 
> > > > > > a better and simpler example is stereo input and mono output
> > > > > > 
> > > > > 
> > > > > In case of stereo → mono with map_channel, you're likely to have something
> > > > > like:
> > > > >     ffmpeg -i stereo.wav -map_channel 0.0.0 left.wav -map_channel 0.0.1 right.wav
> > > > 
> > > > i meant that we have 2 input files, one with right and one with
> > > > left chanel and want one mono output file.
> > > > 
> > > 
> > > Picking from multiple input files is unfortunately not supported ATM
> > > because each output stream is limited to one input stream. Do you see any
> > > other use case for rematrix?
> > > 
> > 
> > Mmh forget this, we might workaround this with the -map.
> > 
> 
> It won't be possible to adapt ffmpeg to this easily AFAIU, so patch
> re-attached adding the mention of the limitation in the documentation.
> 
> The patch is also rebased on master dropping temporarily the two resample
> flag patches (which might need some rework according to the other thread).
> 
> So to sum up, each output stream only has a single associated stream
> (source_index field), so you can't have an output stream based on multiple
> inputs given the current design. Using filters might be a solution, but
> IMHO it does not belong to the scope of this feature.
> 
> Any other suggestion welcome,
[...]
> @@ -176,7 +177,7 @@ int swr_init(SwrContext *s){
>      if(!s->out_ch_layout)
>          s->out_ch_layout= av_get_default_channel_layout(s->out.ch_count);
>  
> -    s->rematrix= s->out_ch_layout  !=s->in_ch_layout;
> +    s->rematrix= s->out_ch_layout != s->in_ch_layout && !s->channel_map;

iam still thinking this is problematic
consider a 5.1 input that has its channels in wrong order and the
user wanting stereo output, this would require remaping channels and
rematrixing and it would be just 1 stream->1 stream

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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