Compressing video using ffmpeg

I use gpu-screen-recorder to create screencasts. The only problem is the resulting videos are huge, which is difficult to share online.

Fortunately, ffmpeg exists.

For decent quality, at a decent file size, quickly

ffmpeg -i input.mp4 -c:v libx264 -crf 25 -preset medium -c:a copy output.mp4

Tests on my machine produce a video file around 80% smaller than the original, at a speed of 1.7x.

For a smaller file, at the cost of speed

ffmpeg -i input.mp4 -c:v libx265 -crf 30 -preset slow -c:a copy output.mp4

Tests produce a file 90% smaller, at a significantly slower speed of 0.4x.

Part of the penalty is due to x265 encoding, and part will be of the "slow" preset.

A thing of note is that I found the CRF value¹ of 25 for x264 was visually indistinct to 30 for x265.

Of course, the speed and perhaps compression rate will differ per machine.