[Mlt-devel] More robust producer lengths?

[anders m. <and...@gm...>]

Hello!

My name is Anders Musikka, and I'm new to this list.

Firstly, let me give a big thank you to everyone contributing to MLT!
It seems to be a very capable, well designed, and needed open source
library.

Recently, I was trying to use openshot to edit a few vacation videos.
I had some trouble. Being a programmer and open source enthusiast, I
traced one of the problems back to MLT.

What had happened was this (I think):

1: Openshot had stored a slightly invalid length of a few of my clips.
2: Openshot specified my clip as a producer for MLT, entering an "in"
and "out" value, where the "out" value was actually one frame after
the real last one in the clip.
3: Openshot then added a few transitions. However, since the actual
length of the clips, as rendered by MLT, weren't the same as the
nominal length (out-in+1), the transitions weren't placed correctly on
the timeline by Openshot, giving unsightly flickering at the start of
fade-ins, for example.

Now, it could probably be argued that there's a bug with openshot.

However, the fact that anyone who uses MLT to compose complex videos,
needs to do a sort of dead reckoning, to try and figure out when in
absolute time each clip will actually start, invites this kind of bug,
and makes it very hard to debug when it occurs.

Would it be possible to change MLT, so that the rendered length of a
clip would always be exactly (out-in+1) frames? I.e, if there aren't
enough frames in the clip, simply repeat the last frame as required?
Maybe provide this behavior as a kind of option?

I'm willing to do some implementation work for this, however I would
need to be pointed in the right direction to be able to come up with a
patch.

best regards,
Anders Musikka