It's a pretty niche case, but if you start a file with no video with
animated ass subtitles and then turned on the video later, the subtitles
would not actually be rendered animated. This because the subtitles were
already decoded, and we do not do a check for animations expect in the
specific case of an image being played back on the video since the check
can be quite expensive. To fix this edge case, we just need to reset the
ass before doing the track switch in the case where we go from no video
to a track that's an image. SD_CTRL_RESET_SOFT is added as a a sub_ctrl
to accomplish this. Fixes#17268.
Dudemanguy
49b6d80e87