[FFmpeg-devel] [PATCH] avformat/mxfdec: support MCA audio information

[Marton Balint]

On Sat, 1 Jan 2022, Pierre-Anthony Lemieux wrote:

> On Sat, Jan 1, 2022 at 5:11 PM Marton Balint <cus at passwd.hu> wrote:
>>
>>
>>
>> On Sat, 1 Jan 2022, Pierre-Anthony Lemieux wrote:
>>
>>> Minor suggestion below.
>>>
>>> In addition, will sample file(s) be added to FATE? Below are two examples:
>>>
>>> http://ffmpeg-imf-samples-public.s3.us-west-1.amazonaws.com/callout_51_l_r_c_lfe_ls_rs.mxf
>>> http://ffmpeg-imf-samples-public.s3.us-west-1.amazonaws.com/callout_51_l_c_r_ls_rs_lfe.mxf
>>
>> Good idea, can someone with access please upload these to the fate mxf
>> folder?
>>
>> [...]
>>
>>> I suggest adding the following audio channels, which are specified in
>>> SMPTE ST 2067-8 [1] and have a direct mapping to ffmpeg audio
>>> channels:AV_CH_STEREO_LEFT
>>>
>>> urn:smpte:ul:060e2b34.0401010d.03020120.03000000 (Left Total) ->
>>> AV_CH_STEREO_LEFT
>>> urn:smpte:ul:060e2b34.0401010d.03020120.04000000 (RightTotal) ->
>>> AV_CH_STEREO_RIGHT
>>>
>>> [1] https://registry.smpte-ra.org/view/published/labels_view.html
>>
>> Unfortunately this is a Dolby encoded stereo mix, not an ordinary LeftOnly
>> / RightOnly mix. So I am not how this should be signalled.
>
> My interpretation below.
>
> In "mov_chan.c", AV_CH_LAYOUT_STEREO_DOWNMIX means
> MOV_CH_LAYOUT_MATRIXSTEREO [1], which is defined in Core Audio [2].
>
> LtRt, i.e. matrix-encoded audio, is not generally Dolby-specific [3].
>
> [1] https://github.com/FFmpeg/FFmpeg/blob/d6b2357eddca392ee137cb2a92ff178a0a7d0cce/libavformat/mov_chan.c#L168
> [2] https://developer.apple.com/documentation/coreaudiotypes/1572101-audio_channel_layout_tags/kaudiochannellayouttag_matrixstereo?changes=_8_7&language=objc
> [3] https://en.wikipedia.org/wiki/Matrix_decoder

Well, ok, I will add these two labels then before pushing.

Thanks,
Marton