ffmpeg

Installing

sudo apt install ffmpeg

Compress a video to h265

 ffmpeg -i example_h264.mp4 -c:v libx265 -crf 24 -preset fast -c:a aac -b:a 128k example_h265.mp4

CRF Info

For H.264 (x264): 

The typical CRF range is 18-28. 

CRF 18: Near lossless quality (very high quality, larger file size). 

CRF 23: Default value, good balance between quality and file size. 

CRF 28: Noticeable quality loss, much smaller file size.

Overwright a videos audio with a new audio track

 ffmpeg -i video_to_overwright.mkv -i audio_input.mp3 -c:v copy -map 0:v:0 -map 1:a:0 output.mp4

MP4 to MP3

 ffmpeg -i filename.mp4 filename.mp3