Blender Git Loki

Fix T91005: Autosplit produces unusable files

Audio PTS was reset for each new file. This caused misalignment of video
and audio streams. In Blender, these files can't be loaded, other
players will fail to align audio and video.

Since timestamps are reset intentionally, reset also video stream
timestamps.

There were other bugs:
After timestamp was reset for audio, write_audio_frames started
encoding from timeline start until target frame, so each split video
had more audio than it should.

Also audio for last frame before splitting was written into new file.

Differential Revision: https://developer.blender.org/D13280