obs-outputs: Use packet time callback for frame-accurate chapter markers

[derrod]

Description

Makes chapter markers frame-accurate by using packet timing callback introduced for BPM.

Motivation and Context

When there is a significant delay between a frame being rendered and submitted to the output, e.g. due to lookahead or audio buffering, the chapter markers would previously be too early in the file as there was no way to determine the packet's original rendering time. This change fixes that.

How Has This Been Tested?

Recorded a video at 30 fps with rc-lookahead=30, confirmed chapter markers are now inserted with a 1-second delay at the correct frame.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• 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.