Video grid with vstack and hstack [duplicate]

Question

I want to combine four videos into a grid. Currently I'm using vstack to combine the rows and then hstack to combine the two outputs, as well as adding the audio.

ffmpeg -ss 0 -i 1.mp4 -ss 8 -i 3.mp4 -filter_complex vstack left.mp4
ffmpeg -ss 0 -i 2.mp4 -ss 0 -i 4.mp4 -filter_complex vstack right.mp4
ffmpeg -i left.mp4 -i right.mp4 -filter_complex hstack -i audio.mp4 output.mp4

It seams possible to do this in one operation using overlay and pad. However, the documentation states that using vstack and hstack is faster. Can those two filters be combined to one single operation?

Answer 1

You can do it all in one command using the hstack and vstack filters.

ffmpeg -i top_l.mp4 -i top_r.mp4 -i bottom_l.mp4 -i bottom_r.mp4 -i audio.mp4 \
-filter_complex "[0:v][1:v]hstack[t];[2:v][3:v]hstack[b];[t][b]vstack[v]" \
-map "[v]" -map 4:a -c:a copy -shortest output.mp4

• The audio will be stream copied from audio.mp4 instead of being needlessly re-encoded.

If you want the audio from each input to be combined instead of providing a separate audio input then use the amerge filter. -ac 2 is added to downmix to stereo; otherwise the output would have a cumulative number of audio channels.

ffmpeg -i top_l.mp4 -i top_r.mp4 -i bottom_l.mp4 -i bottom_r.mp4 -filter_complex \
"[0:v][1:v]hstack[t];[2:v][3:v]hstack[b];[t][b]vstack[v]; \
 [0:a][1:a][2:a][3:a]amerge=inputs=4[a]" \
-map "[v]" -map "[a]" -ac 2 -shortest output.mp4