Queries on: Fixed position and style formatting for EBU-TT-D subtitles

[Brainiarc7]

System info

Operating System: Ubuntu 22.04
Shaka Packager Version: main, git tip

Issue and steps to reproduce the problem:

This is a query on the current state of Fixed position and style formatting for EBU-TT-D subtitles in shaka-packager.
As highlighted on this PR, EBU Teletext input following Level 1.5 of the core specification ETSI EN 300 706 V1.2.1 (2003-04) and webvtt in MP4 segments output are implemented. This works well, as tested.

However, fixed position and style formatting for the same aren't implemented (yet), which raises two questions:

1. Can this be extended to match what Amazon's Medialive implementation achieves?

2. Is such a feature within the scope of a downstream packager such as Shaka?

[tobbee]

I'm working on adding vertical positioning, approximative alignment (calculated from text positions to be left, center, and right) as well as text color. Should hopefully have a PR before the end of the month (March 2024).

[cosmin]

Closed by #1384