[FFmpeg-user] more sound madness

Ted Park kumowoon1025 at gmail.com
Sat Mar 7 19:05:05 EET 2020


> Hi Ted,
> Sorry, I have no clue what you mean here, could you please elaborate?
I am not sure if this is accessible with ffmpeg, but in the track header, usually only tracks with different alternate_group, or 0, can play at the same time.

> Nope, moving the  does not make any difference.
> Did you try this yourself? Does it work for you?
I mean, yes, but it works either way. But the source I used was a single mxf with multiple tracks, I didn’t try multiple inputs or a bwf.

>>> 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.
> trust me, it does matter. First input file gets the audio enabled, all other gets muted in metadata.
Oh right… But I mean they don’t matter if your tracks aren’t randomly disabled. I still would have thought at least one would get chosen.
When you say muted in metadata, do you literally mean they have their relative volume set to 0 per track?
Either way, I’m pretty sure it is because some channels overlap between the two inputs, I think this filter is what is actually being attempted, give it a try.
% ffmpeg -i /Volumes/Data/test/C0092.MP4 -i /Volumes/Data/test/068.WAV -filter_complex “[0:1]pan=1c|c0=c1[o1];[1:0]pan=1c|c0=c9[o2];[1:0]pan=1c|c0=c10[o3]” -map “[o1]" -map “[o2]" -map “[o3]"
 -c:a pcm_s24le -map 0:0 -c:v copy -shortest /Volumes/Data/test/last2muted.mov -y

> there is no ‘normal’ in my world, and the Mov format accepts virtually unlimited channels in virtual unlimited tracks in virtual unlimited combinations, so that ‘should’ not be an issue.
The manual panning sets all tracks as mono, at channel 0. The mov format has very little restrictions, but what is supported by software is a different story.

>> or how the extra channels are mapped wrt gain. Exploding the multitrack recording into separate wave files first might make things simpler.
> SImpler in what way?
> Sorry, but merging two files ‘should’ be possible IMHO, and I’m fighting on doing this for a couple of days now, so ‘simple’ is not in my book anymore.
Yes I agree, it was just an alternative because what should be working doesn’t seem to be. It’s simpler since you don’t have to worry about the channels being in a known layout for one thing.

Ted Park

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