aja: Subtract packet time from audio timestamp

[norihiro]

Description

Subtract the audio packet time from the timestamp for audio.
The code is copied from pulse-input.c.

Motivation and Context

When calling obs_source_output_audio, timestamp should be the starting time of the audio packet.

How Has This Been Tested?

OS: Fedora 34.
Hardware: AJA Video Kona 4 (connected to the top PCIe slot)
CPU: Intel Core i7-11700
MB: ASRock Z590 Extreme (no GPU card is installed)
Camera: Sony SRG-120HD (configured to send 1080p59.94)
I found the bug during implementing another PR #6351.
The implementation was tested with debug information in the change of the PR.

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.

[jp9000]

What's the average duration of an audio segment for aja?

[norihiro]

On my setup, it sends 800 frames for each packet at 48000 Hz in average, so 16.7 ms, it varies 784 to 816 samples.

[norihiro]

It looks the segment time of the audio equals to the video frame time. If I configure my camera to 25 fps, the size of the segment becomes 1920 frames, 40ms.