Command-line video editing?

[Linguist]

Does anyone know of commercially/freely available packages that can add watermarks/extra frames to videos and re-encode them back into original format?

Or at least something with a similar functionality?

[Helix]

you might find AviSynth interesting.

[Linguist]

you might find AviSynth interesting.

Looks like just what I need! Thanks a LOT!

[quantum-x]

ffmpeg .

[Linguist]

ffmpeg .

Ffmpeg also looks awesome, and seems to support mannyy formats.

Thanks for the advice guys! Looks like I've now got quite a number manual pages to go through