[FFmpeg-user] isolate 'voices', move them, and mix into another audio stream

[Paul B Mahol]

On Sun, Jun 1, 2025 at 7:42 PM Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 01/06/2025 15.38, Paul B Mahol wrote:
> > On Sun, Jun 1, 2025 at 7:37 PM Mark Filipak <markfilipak.imdb at gmail.com>
> > wrote:
> >
> >> On 01/06/2025 14.26, Paul B Mahol wrote:
> >>>> Am 01.06.25 um 17:48 schrieb Paul B Mahol:
> >>>>> On Sun, Jun 1, 2025 at 3:40 PM Mark Filipak <
> >> markfilipak.imdb at gmail.com>
> >>>>> wrote:
> >>>>>> I have two ac3 audio streams. One is 'voices+noise', the other is
> just
> >>>>>> 'noise' -- no voices. I want
> >>>>>> to take 'voices+noise', remove 'noise' leaving just 'voices', then
> mix
> >>>>>> 'voices' into a latter,
> >>>>>> clipped version, call it 'sounds'. I could do it with Audacity, but
> >> I'd
> >>>>>> like to do it with FFmpeg,
> >>>>>> if possible.
> >>>>>>
> >>>>>> I seek experienced guidance because I've never done this before and
> I
> >>>> want
> >>>>>> to use the best audio
> >>>>>> mixer 'filter' available -- knowing what's best comes only via
> >>>> experience.
> >>>>>>
> >>>>>> The full story:
> >>>>>>
> >>>>>> "2001, A SPACE ODYSSEY" has a tedious, 2:58.136 prelude that is just
> >>>>>> 'noise', after which the MGM
> >>>>>> Lion appears. When I made an mp4, I cut 'm2ts 0..178.136' out
> leaving
> >>>> just
> >>>>>> 'm2ts 178.136...', which
> >>>>>> is now 'mp4 0...', which begins with the MGM Lion.
> >>>>>>
> >>>>>> When I finished, I discovered that in their comments track, Keir
> >> Dullea
> >>>>>> and Gary Lockwood introduce
> >>>>>> themselves during that 'noise'. Their 'voices' spans 'm2ts
> 0..34.034'.
> >>>>>>
> >>>>>> I want to take 'm2ts 0..34.034', remove the 'noise' so that only
> >>>> 'voices'
> >>>>>> is left, then mix 'voices'
> >>>>>> into 'mp4 0..34.034', over the MGM Lion. There's a little more
> >> clipping
> >>>>>> and joining to be done but I
> >>>>>> can handle that.
> >>>>>>
> >>>>> Need actual files.
> >>>
> >>> I need exact files that Mark have.
> >>
> >> Why, Paul? This isn't troubleshooting. It's how-to.
> >>
> >> I need to do this:
> >>
> >> 1) 'voices' = mix('voices+noise',invert('noise')). 'voices+noise' is an
> >> existing ac3. 'noise' is
> >> another ac3 that is identical but without voices. 'amix' is a mixer, but
> >> is it the best mixer? More
> >> important: I don't know of any audio filter that will invert().
> >>
> >> followed by this:
> >>
> >> 2) output = mix('audio','voices'). 'audio' is an existing ac3.
> >>
> >
> > How many audio channels every file have?
>
> It's stereo ac3, 192kbpx. Do you need the files to run experiments?
>

And why do you think noise is exactly same as in another file?

You can mix audios with amix filter.
And you can change weights to -1 in amix too with special option.
See documentation of amix filter.

So something like:

ffmpeg -i voice.ac3 -i noise.ac3 -lavfi "amix=weights=1 -1" out.wav


But I really doubt you will accomplish anything with that.


>
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