[Ffmpeg-devel] [PATCH] audio channel extraction

[Axel Holzinger]

Good evening :-)

> Hi
>
> On Fri, Sep 15, 2006 at 06:08:06PM +0200, Axel Holzinger wrote:
> > Hi
> >
> > > Hi
> > >
> > > On Fri, Sep 15, 2006 at 02:21:13PM +0200, Baptiste Coudurier wrote:
> > > > Michael Niedermayer wrote:
> > > > > Hi
> > > > >
> > > > > On Fri, Sep 15, 2006 at 12:47:20PM +0200, Baptiste
> Coudurier wrote:
> > > > >> Hi
> > > > >>
> > > > >> This patch adds feature to extract specific channels from
> > > audio track.
> > > > >> My main goal was to split 4 channels tracks to 2 stereos tracks.
> > > > >
> > > > > what about a more generic system which could mix chanels
> together into
> > > > > other channels? so that there would be a AxB matrix of
> coefficients to
> > > > > mix A input channels into B output channels?
> > > > >
> > > > >
> > > > > [...]
> > > >
> > > > That would be a nice idea indeed, and would that be usefull
> for ac3/aac
> > > > downmixing also ?
> > >
> > > i think so
> > >
> > >
> > > > I might lack theory and good design skills to do that
> > > > though :/
> > > > Could you point me papers, or design ideas ?
> > >
> > > just leave the coefficients to the user as command line parameters
> >
> > bad idea as the ac3 data already tells you how to downmix
> >
> > or do you think the user shall read the ac3 data directly to
> find out how to
> > downmix?
>
> if a stream contains information on how to downmix and the number
> of channels the user wants matches then this could be used as
> default if the user doesnt specify any other coefficients

exactly

> but extracting these coefficients from the stream and supporting
> downmixing based on user specified coeffs are 2 seperate things

that's what i mean
but if i'm not already sleeping, it looks to me that this makes it necessary
to extend the codec interface to obtain the default downmix coefficients

Good night
Axel