I will have to check this bit more in detail, I would expect to see SEQ_set_data_from_anim only in seq_render_movie_strip.

Also requiring duration for rna_Sequences_new_movie is quite bad idea I think, because how are you supposed to know what file duration is before it is added? Also people may not notice that this causes files to be not loaded and reading movie specific properties would result in incorrect values. This would be solved by calling SEQ_set_data_from_anim from RNA get/set functions though, but still. I would rather add boolean argument to skip file loading, so it has to be enabled explicitly.

Also requiring duration for rna_Sequences_new_movie is quite bad idea I think, because how are you supposed to know what file duration is before it is added? Also people may not notice that this causes files to be not loaded and reading movie specific properties would result in incorrect values. This would be solved by calling SEQ_set_data_from_anim from RNA get/set functions though, but still. I would rather add boolean argument to skip file loading, so it has to be enabled explicitly.

duration isn't required, I made it optional in the case where you already know it, when you build an editing from a file for example.

I thought about a boolean, but to me it didn't make sense to skip_opening and not setting the duration. Because you end up with one frame files. And this boolean system requires you to know you must update duration after creation, which is not intuitive and source of mistakes.