[FFmpeg-user] DTS 7.1 to AC3 5.1

[Paul B Mahol]

On Thu, May 22, 2025 at 8:30 PM Paul B Mahol <onemda at gmail.com> wrote:

>
>
> 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.
>

I know why this is happening, the channel layout type negotiation in
libavfilter is sub-optimal there.

>
>
>> _______________________________________________
>> ffmpeg-user mailing list
>> ffmpeg-user at ffmpeg.org
>> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
>>
>> To unsubscribe, visit link above, or email
>> ffmpeg-user-request at ffmpeg.org with subject "unsubscribe".
>>
>