Convert a video to another format

Worked example

Some conversions need no encoding at all — they just repackage the same streams in a different container.

The equivalent command

ffmpeg -i holiday-clip.mp4 -c:v libvpx-vp9 -crf 32 -b:v 0 -pix_fmt yuv420p -deadline realtime -cpu-used 5 -c:a libopus -b:a 128k -threads 1 -y out-holiday-clip.webm

This is exactly what runs in the browser. Copy it to run the same job locally on a file too large for a tab.

Why it matters

"Converting" covers two very different jobs. Changing the container — MP4 to MKV, say — can often be done by copying the existing video and audio packets into the new wrapper, which is instant and lossless. Changing the codec, as MP4 to WebM requires, means decoding and re-encoding every frame. The tool works out which applies and tells you, because one takes a second and the other takes minutes.

What this needs

A 30.7 MB FFmpeg download, cached by your browser after the first time. Nothing is downloaded until you click.