[32.1.0] Media Source not showing in Audio Mixer on macOS (regression from 31.x)

Operating System Info

macOS

Other OS

No response

OBS Studio Version

32.1.0

OBS Studio Version (Other)

No response

OBS Studio Log URL

No response

OBS Studio Crash Log URL

No response

Expected Behavior

Media Source should appear in the Audio Mixer with volume control, just like in version 31.0.4.

Current Behavior

After upgrading to 32.1.0, Media Source does not show in the Audio Mixer at all.
Downgrading to 31.0.4 fixes the issue - Media Source appears correctly in the mixer.

Steps to Reproduce

1. Open OBS Studio 32.1.0
2. Add a Media Source (video file with audio)
3. Check the Audio Mixer - Media Source is not visible
4. No volume control available for the media source
5. Play the media - still no audio meter or volume control in mixer

Anything else we should know?

This appears to be a regression caused by PR #13118 "frontend: Ignore sources with disabled audio in mixer".

The obs_source_audio_active() check may not correctly detect media source audio as "active" even when the media is playing.

This works correctly in:

• OBS Studio 31.0.4 ✓

This is broken in:

• OBS Studio 32.1.0 ✗

The issue affects macOS users who rely on Media Source for video/audio playback with mixer control.

Reproduce the missing Media Source mixer entry on macOS with OBS Studio 32.1.0, then compare it with 31.0.4. Start by reviewing PR #13118 and the obs_source_audio_active() check; done means a playing Media Source appears in the Audio Mixer with an audio meter and volume control.