[Ffmpeg-devel] Applying vhooks to only some output streams

[James Le Cuirot]

Hi guys. I am using ffmpeg to encode two videos at once. I'm also using
the watermark vhook. Ideally I'd like to only apply the watermark to
just one of the videos but as far as I can tell, this isn't possible at
the moment. I could just encode the videos separately but time is
crucial and this actually operates behind the scenes of a web front
end, which makes it a little flakey. The less times I have to run
ffmpeg, the better!

I had a quick look at the source to see whether it was feasible. I
thought that maybe it would work if a copy of each frame were made
before applying the hooks. Which frame then gets sent to the output
each stream would depend on the position of the vhook argument.

ffmpeg -i foo.avi bar1.avi bar2.avi -vhook "blah.so" bar3.avi bar4.avi

So in the above example, the hook would only be applied to bar3.avi and
bar4.avi. For multiple vhooks, I guess you could restrict it to applying
either all or none of them, otherwise it would get too messy. So would
this work or am I being naive here?

James