[giantrobot]

Text with video is difficult to do correctly for a few different reasons. Just rendering text well is a complicated task that's often done poorly. Allowing arbitrary text styling leads to more complexity. However for the sake of accessibility (and/or regulations) you need some level of styling ability.

This is all besides complexity like video/audio content synced text or handling multiple simultaneous speakers. Even that is besides workflow/tooling issues that you mentioned.

The MPEG-4 spec kind of punted on text and supports fairly basic timed text subtitles. Text essentially has timestamp where it appears and a duration. There's minimal ability to style the text and there's limits on the availability of fonts though it does allow for Unicode so most languages are covered. It's possible to do tricks where you style words at time stamps to give a karaoke effect or identify speakers but that's all on the creation side and is very tricky.

The Matroska spec has a lot more robust support for text but it's more of just preserving the original subtitle/text encoding in the file and letting the player software figure out what to do with that particular format and then displaying it as an overlay on the video.

It's unfortunate text doesn't get more first class love from multimedia specs. There's a lot that could be done, titles and credits as you mention, but also better integration of descriptive or reference text or hyperlink-able anchors.