FFmpeg
Some FFmpeg snippets for pre-processing video files.
Preprocessing videos for editing in Final Cut Pro
It often happens that files downloaded from livestreams makes Final Cut Pro very laggy. One workaround is to use ffmpeg to re-encode the file once before editing. There will be a bit of quality hit, but the effect is minimal.
ffmpeg -i IN.mp4 -vcodec libx265 -tag:v hvc1 -crf 18 OUT.mp4
Note: hvc1 tag is required for AVKit to playback properly.
draft
Using M1's GPU to preprocess video
By using libx265 encoder might causes your Mac to ran out of CPU for a very long time. If you're able to sacrifice post-preprocessed massive file size for a faster speed. Then hevc_videotoolbox would be handy as well.
First do a ffprobe to determine input video's bitrate.
ffprobe -v quiet -select_streams v:0 -show_entries stream=bit_rate -of default=noprint_wrappers=1 IN.mp4
This command will answer video bitrate in bits unit.