feat: add "loop" video option

[BowgartField]

Hi,
This PR add the loop (boolean) option to a layer of type video.

✅ Infinit loop on a video layer type.
✅ Fmmpeg stream not gently closed causing error at the end of the encoding (not critical)
❌ Should check that clip have just one video layer

[BowgartField]

There is the error:

[BowgartField]

maybe -stream_loop should be changed to -vf loop=loop:start=xxx:end=xxx to allow cutFrom and cutTo ?

EDIT:
Not working. Need to find a way to determine frame index of cutTo and cutFrom time