How can I speed up this side by side video stitch in FFMPEG

Question

I have two videos the same size and pixel format (about 240x360) left and right that I want to stitch together.

I'm using:

ffmpeg -i left.mp4 -i right.mp4  -filter_complex "[0:v][1:v]hstack=inputs=2:shortest=1[v]; [0:a][1:a]amerge[a]" -map "[v]" -map "[a]" -ac 2 -shortest -y output.mp4

which takes about 15 seconds on a 3 core machine. I see x1.25 on the conversion line.

I know this isnt too bad, but any speed up I can make is going to help a lot as its in heavy use.

Any ideas how I can improve this?

Answer 1

Use a fast -preset

Assuming you are using the encoder libx264 for the MP4 output you can use a faster -preset. See FFmpeg Wiki: H.264.

ffmpeg -i left.mp4 -i right.mp4 -filter_complex "[0:v][1:v]hstack=inputs=2:shortest=1[v]; [0:a][1:a]amerge[a]" -map "[v]" -map "[a]" -preset veryfast -ac 2 -shortest -y output.mp4

Not much else you can do as the encoder is already optimized.

Use your player instead

If you only need to play the files side-by-side, and don't need an output file, you can have your player do it and avoid any need for encoding. See Multiple side-to-side video streams in one file without transcoding.