[Ffmpeg-devel] channel ordering and downmixing

Benjamin Larsson banan
Thu Apr 5 11:07:18 CEST 2007

Justin Ruggles wrote:
> Hi,
> Justin Ruggles wrote:
>> I need some advice on a channel ordering and downmixing framework.  I've
>> been trying to figure out the best solution for a while and keep running
>> into road blocks.
> After spending too much time just pondering different ideas, I decided
> to give it a go and try one out.
> The attached patch isn't really meant to be a working patch, but more of
> a conceptual sketch of a basic design.  I want to get ideas and comments
> before taking the time to implement it in full.
> The general concept is:
>  - add an AVChannelLayout struct to AVCodecContext
>  - have the muxer set its preferred channel layout in read_header()
>  - have the decoder override the channel layout if it wants to
>  - user-level API: av_channel_mix_init(), av_channel_mix(),
>                    av_channel_mix_close()
>  - the encoder can set the channel layout in encode_init or just set the
>    number of channels and set the mask to CHANNEL_MASK_NONE to let the
>    muxer decide
>  - if avctx->channel_layout.mask is CHANNEL_MASK_NONE, the muxer should
>    set the channel layout
> Any suggestions/critiques would be great. :)
> -Justin

Don't forget the dts down mixing coeffs. Anyway I think the codecs
should have the layout and down mixing coeffs, not channelmix.c but that
is just a technicality. DTS for example has the ability to use coeffs
from the actual bitstream.

Benjamin Larsson

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