ffmpeg

Extracting sound from a video and save it as MP3.

fmpeg -i path/to/video.mp4 -vn path/to/sound.mp3

Creating a gif from a video.

ffmpeg -i path/to/video.mp4 -filter:v 'scale=-1:960' -r 15 path/to/output.gif

Capturing screen, webcam, etc is also possible, but need to figure how as it's device specific.

ffmpeg -video_size 1024x768 -framerate 25 -f x11grab -i :0.0+100,200 -f alsa -ac 2 -i hw:0 output.mkv

References

• ffmpeg Documentation