[FFmpeg-devel] MOV: center channel 'chan' metadata

Carl Eugen Hoyos ceffmpeg at gmail.com
Sat Mar 17 15:29:36 EET 2018

2018-03-17 3:33 GMT+01:00, Courtland Idstrom <cidstrom at telltalegames.com>:
> Hi -
> I'm working with a post-production workflow to mux 5.1 wav audio into a mov
> file (each channel specified as a separate track), with correct channel
> assignments written as metadata. I'm able to get everything except for the
> Center channel to appear correctly when viewed in Quicktime, however the
> Center channel shows up as 'mono'.
> I'm using a command like this (other channels omitted for the sake of
> brevity):
> ffmpeg -i input.mov \
>   -i audio.wav \
>  -filter_complex "[1:0]pan=FC|c0=c0[FC]" \
>  -map 0:v \
>  -map "[FC]" \
>  -c:v copy \
>  -c:a pcm_s24le \
>  output.mov
> This ends up writing a 'chan' tag that indicates Mono content
> (MOV_CH_LAYOUT_MONO). If I use a different channel, such as "FL", it writes
> a value that Quicktime understands (layout=MOV_CH_LAYOUT_USE_BITMAP
> bitmap=0). After some tracing, it appears that this configuration comes
> from the layout defined in mov_ch_layout_map_1ch for a single center
> channel. This seems like intended functionality and not a bug, but
> unfortunately doesn't solve my issue.

You could still send a patch that changes this mapping to get some feedback.
(I am not a fan but if there is no other simple solution...)

Carl Eugen

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