ffmpeg

ffmpeg -i video.avi

  # ls *.mkv >> list.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'

ffmpeg -f concat -i list.txt -c copy output
ffmpeg -i "concat:file1.mpg|file2.mpg|file3.mpg" -c copy output.mpg

### Merge images as video
ffmpeg -f image2 -i img%d.jpg video.mpg
### Or the opposite way
ffmpeg -i video.mpg img%d.gif

### Crop to 1080x1080
ffmpeg -i input.mp4 strict -2 -vf crop=1080:1080:0:420 output.mp4
### Split with timestamp
ffmpeg -i input.mp4 -vcodec copy -acodec copy -ss 0:12:34 -t 0:10:00 10.mins.split.mp4

### Scale 1080p to 480p
ffmpeg -i input.mp4 -vf scale=853:480 -acodec aac -vcodec h264 output.mp4
### Convert avi to mp4
ffmpeg -i input.avi -c:v h264 output.mp4
ffmpeg -i input.avi -c:v libx264 -crf 24 output.mp4
### Convert between avi and mpg, gif
ffmpeg -i video.avi video.mpg
ffmpeg -i video.mpg video.avi
ffmpeg -i video.avi anime.gif
### Extract audio from video
ffmpeg -i video.avi -vn -ar 44100 -ac 2 -ab 192 -f mp3 sound.mp3
### Encapsulation video and audio files into mp4/mkv
ffmpeg -i video.avi -i audio.aac -vcodec copy -acodec copy output.mp4