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

[Marton Balint]

On Sun, 2 Jan 2022, Marton Balint wrote:

>
>
> 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.

Will push and backport this tomorrow.

Regards,
Marton