coreaudio-encoder: Fix pts/dts not including encoder delay

[derrod]

Description

Note

Requires #10689 to be fully functional as currently OBS will not treat negative audio timestamps correctly.

CoreAudio - and other AAC encoders - generally have an encoder delay that produces a number of silent "priming" samples. For CoreAudio AAC this is 2112 by default and this needs to be subtracted from the PTS/DTS to ensure that PTS 0 is the actual start of the input audio.

See Apple's documentation for a good explanation of AAC encoder delay and how to deal with it: https://web.archive.org/web/20170912012230/https://developer.apple.com/library/content/documentation/QuickTime/QTFF/QTFFAppenG/QTFFAppenG.html

Motivation and Context

Want audio to be in sync.

When using FFmpeg encoders libavcodec already handles this for us. This is also already done in the libfdk-aac module: https://github.com/obsproject/obs-studio/blob/master/plugins/obs-libfdk/obs-libfdk.c#L266-L272

How Has This Been Tested?

Validated on Windows that output DTS/PTS is now correct.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

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.