[FFmpeg-user] Copying all audio channels and create mixdown at the same time

[Paul B Mahol]

On 8/22/17, Lou <lou at lrcd.com> wrote:
> On Tue, Aug 22, 2017, at 08:15 AM, Steve Dierker wrote:
>> Hello list,
>>
>> I have an MXF file with one video track and 8 audio track. I'm trying to
>> reencode it to MP4 while preserving all existing tracks and also adding
>> a mixdown of all audio tracks as the 9th track.
>> Right now I'm only able to do this in 2 separate FFmpeg calls and I'm
>> wondering whether one can do it in one call.
>>
>
> ffmpeg -i input -filter_complex
> "[0:a:0][0:a:1][0:a:2][0:a:3][0:a:4][0:a:5][0:a:6][0:a:7]amerge=inputs=8[mix]"
> -map 0 -map "[mix]" output
>
> Or if you want to be lazy and blindly trust amix to choose inputs for
> you:
> ffmpeg -i input -filter_complex "amerge=inputs=8[downmix]" -map 0 -map
> "[mix]" output

amerge is not an amix.

amerge merges while amix mixes streams.