[FFmpeg-user] DTS 7.1 to AC3 5.1

[Paul B Mahol]

On Thu, May 22, 2025 at 8:22 PM Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 22/05/2025 16.07, Paul B Mahol wrote:
> > On Thu, May 22, 2025 at 8:01 PM Mark Filipak <markfilipak.imdb at gmail.com
> >
> > wrote:
> >
> >> Hi, All,
> >>
> >> I've tried every trick in the documentation but I can't persuade FFmpeg
> >> CLI to convert DTS 7.1 to
> >> AC3 5.1.
> >>
> >> The best I get is AC3 5.0(side).
> >>
> >> Handbrake does it, and it uses the same libraries! I went ahead and
> made a
> >> minimal-resolution, MPEG2
> >> copy just to get at the AC3 5.1.
> >>
> >> Do you do DTS 7.1 to AC3 5.1 via FFmpeg? How do you do it?
> >>
> >>
> >>         silent = 3,214,906,938 bytes
> >> with DTS 7.1 = 8,623,235,367 bytes
> >> with AC3 5.1 = 3,968,811,052 bytes
> >>
> >
> > Use librempeg instead:
> >
> > ffmpeg -i 7_1.m2ts -af acl2cl=5.1 -vn x.ac3
>
> Thank you, Mr. Mahol. 'acl2cl' is not documented. But I will try it.
>
> The try will likely fail because 'librempeg' appears to be lacking in Mr.
> Doshi's builds. Hopefully,
> I'm wrong about that.
>

There is windows librempeg build on github fork. If you use github search
you can easily find it (if you have github account).

You can use similar/same with pan filter in ffmpeg:

ffmpeg -i input.m2ts -af "pan=5.1|FL=FL|FR=FR|FC=FC|LFE=LFE|BL=BL|BR=BR"
output.ac3

why this is not the default with aresample/aformat in FFmpeg is strange.


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