Conversion from timeline frame to frame index was done by casting to
integer, which followed logic of ffmpeg seeking. However this is not
best approach in some cases - for example when FPS of scene and movie
differs by a very small amount. In this case the first frame could be
duplicated and all other frames will appear as offset by one frame.
In particular this may happen scene is set to 29.97 fps and movie is
encoded at 30000/1001 fps. A frame will still have to be duplicated, but
it should be frame where decimal of frame index crosses 0.5 to keep
audio and video in sync as best as possible.
Pull Request: https://projects.blender.org/blender/blender/pulls/113870
c7384ba6f3