[FFmpeg-user] Downmixing an audio stream while keeping a copy of the original stream

[Adam Baxter]

On 23 December 2017 at 21:24, Kieran O Leary <kieran.o.leary at gmail.com>
wrote:
>
>  ffmpeg -i "out.mkv" -map 0:v -c:v copy -c:a:0 aac -b:a:0 192k -ac:a:0
> 2 -filter_complex
> "[a:0]pan=stereo|FL=FC+0.30*FL+0.30*BL|FR=FC+0.30*FR+0.30*BR[a]" -map
> [a] -map a:0:1 -c:a:1 copy "output.mkv"
>
>
I think our command lines now match up: ffmpeg -i "input.mkv" -map 0:v -c:v
copy -c:a:1 copy -c:a:0 aac -b:a:0 192k -ac:a:0 2 -filter_complex
"[a:0]pan=stereo|FL=FC+0.30*FL+0.30*BL|FR=FC+0.30*FR+0.30*BR[a]" -map [a]
-map a:0:1 -c:a:1 copy "output.mkv"

This works perfectly, but I really don't understand how! I especially don't
understand the [a] at the end of the filter. I'll try to clean up the
command line a bit tomorrow to make some sense of it.

Thanks for your help.

--Adam