[FFmpeg-user] more sound madness

Ted Park kumowoon1025 at gmail.com
Sat Mar 7 15:38:04 EET 2020


> command below seems simple enough, and works, except that the last two audio channels (those coming from the second input) are muted in the metadata.
> (Meaning, the sound data is there, but QT atom has flagged them as ‘inactive’.)

> What is the secret handshake to remap / patch / reroute / matrix / add / omit the sound channels of multiple input files to one new file?
> (I can’t imagine I’m the only one doing this kind of stuff. And at this point I really don’t care if all the channels end up in one track, or in multiple, just to have them play in QT / Premiere and alike.)
The reverse of “inactive” is “default” iirc, so they aren’t in alternate groups. The mov muxer seems to do that by default for me though.

> bouke at Boukes-iMac ~ % /Applications/ffmpeg  -i /Volumes/Data/test/C0092.MP4 -i /Volumes/Data/test/068.WAV -map 0:0 -map 0:a -map_channel 0.1.1:0.1  -map 1:a -map_channel 1.0.8:0.2 -map 1:a -map_channel 1.0.9:0.3  -c:a pcm_s24le -c:v copy -shortest /Volumes/Data/test/last2muted.mov -y

I think it would help to do the channel mapping first just to separate the options
% ffmpeg -i /Volumes/Data/test/C0092.MP4 -i /Volumes/Data/test/068.WAV -map 0:1 -map 1:0 -map 1:0 -map_channel 0.1.1:0.1 -map_channel 1.0.8:0.2 -map_channel 1.0.9:0.3 -c:a pcm_s24le -map 0:0 -c:v copy -shortest /Volumes/Data/test/last2muted.mov -y

> Stream mapping:
>  Stream #0:0 -> #0:0 (copy)
>  Stream #0:1 -> #0:1 (pcm_s16be (native) -> pcm_s24le (native))
>  Stream #1:0 -> #0:2 (pcm_s24le (native) -> pcm_s24le (native))
>  Stream #1:0 -> #0:3 (pcm_s24le (native) -> pcm_s24le (native))
> Press [q] to stop, [?] for help
> -map_channel is forwarded to lavfi similarly to -af pan=0x4|c0=c1.
> [pan @ 0x7fb020e00a00] Pure channel mapping detected: 1
> -map_channel is forwarded to lavfi similarly to -af pan=0x4|c0=c8.
> [pan @ 0x7fb020d04740] Pure channel mapping detected: 8
> -map_channel is forwarded to lavfi similarly to -af pan=0x4|c0=c9.
> [pan @ 0x7fb020f1d200] Pure channel mapping detected: 9

It shouldn’t matter if audio channels come before others. Also I am kind of suspicious of this, I don’t know if using 4 channels is normal in this situation, or how the extra channels are mapped wrt gain. Exploding the multitrack recording into separate wave files first might make things simpler.
Ted Park

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