obs-ffmpeg: Add support for multiple video tracks to ffmpeg-mux

[kc5nra]

Depends on https://github.com/obsproject/obs-studio/pull/8093

Description

• Add support for multiple video tracks to ffmpeg-mux.
• Allows sparse video encodes (idx 1, 3,4)

Motivation and Context

• Multi-program mpegts
• Multiple angles in a single video
• Network protocols that support multiple resolutions

How Has This Been Tested?

Tested saving multiple resolutions as distinct tracks to a mkv

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [ ] The code has been tested.
• [ ] All commit messages are properly formatted and commits squashed where appropriate.
• [ ] I have included updates to all appropriate documentation.

[jp9000]

Any particular protocols or anything like that you're interested in for this case? Or is this more just like a proof-of-concept implementation for #8093?

[kc5nra]

Any particular protocols or anything like that you're interested in for this case? Or is this more just like a proof-of-concept implementation for #8093?

As you surmised, used while testing. Will support any multi-video protocol that ffmpeg supports so .. I could seem some uses there but yeah :-)

There are some "bugs" fixed here around audio tracks, but bugs could be debatable and it makes fairly extensive changes to address them