By Joel Dare - Written June 6, 2025
I often need to resize video for use on the web.
Especially video created by recording my screen with Quicktime on MacOS, which tends to be rather large by default.
Here’s a quick ffmpeg command you can use to resize to something more reasonable.
ffmpeg -i input.mov \
-vcodec libx264 -crf 23 -preset fast \
-acodec aac -b:a 128k \
-movflags +faststart \
output.mp4
-I input.mov specifies your source video file.
-vcodec libx264 uses the H.264 video codec, which has good we support.
-crf 23 sets a constant rate factor, lower for better quality and a larger file. The range is 0–51 with 23 being a good default.
-preset fast is a good trade-off between encoding time and compression. The options are: ultrafast, superfast, veryfast, faster, fast, medium (default), slow, slower, veryslow. Use slow or slower for better compression/quality at the cost of speed.
-acodec aac uses AAC audio, which is widely supported.
-b:a 128k sets the audio bitrate.
-movflags +faststart optimizes the file for web streaming by moving metadata to the beginning of the file.
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