Optional preprocessing of source subtitles

[machinewrapped]

Adds a system to optionally preprocess input subtitles when they are loaded. This can fix some common issues that make translations less accurate or more error prone. It is particularly useful for subtitles generated with Whisper:

• Split long lines. Attempt to break long lines by splitting at newlines or punctuation, setting the duration of the split sections proportional to their length.
• Attempt to identify dialog markers indicating a change of speaker that are on the same line (common in Chinese subtitles) and add line breaks
• Attempt to ensure that if any lines begin with a dialog marker then all lines do

These functions are inspired by the Fix Common Errors tool in Subtitle Edit, though they work a little differently. More may be added in future - create an issue or discussion if there is something you see regularly that could be fixed automatically.

The preprocess step is not enabled by default, but it can be turned on in the settings dialog (which will add a tab with settings for the preprocessor) or in the new project dialog, so you can see how much difference it makes to the line and batch count.

---

This discussion was created from the release Optional preprocessing of source subtitles.