linux-v4l2: Adjusting camera controls (Zoom, Focus, etc.) triggers stream restarts on USB3 4k webcam (Elgato 4k facecam)

Operating System Info

Other

Other OS

CachyOS

OBS Studio Version

32.2.2

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/VSSgX2ym6OQxeCBf

OBS Studio Crash Log URL

No response

Expected Behavior

1. Click the + button to add a new source or right click to edit the properties of an existing V4L2 source
2. Go to settings like zoom that have a slider
3. It sets the setting without issue

Current Behavior

1. Click the + button to add a new source or right click to edit the properties of an existing V4L2 source
2. Go to settings like zoom that have a slider
3. It sets the setting but the webcam will have a flashing blue light and drop frames

Steps to Reproduce

Basically as described in the current behaviour. I tried mainly with the zoom setting.

Anything else we should know?

I already dug into the issue myself already. I think the issue is related to the v4l2_settings_changed method:

https://github.com/obsproject/obs-studio/blob/master/plugins/linux-v4l2/v4l2-input.c#L989-L1026

What happens is:

res |= (data->framerate != obs_data_get_int(settings, "framerate")) &&
(obs_data_get_int(settings, "framerate") != -1);

Will always be evaluated as true because 60fps is the frame rate in the settings and the v4l2_framerate_list returns a packed tuple so you get for 60fps a comparison of 4294967356 != 60 so always true. That calls v4l2_terminate and v4l2_init because it assumes it needs a restart every time the slider moves.

Start in plugins/linux-v4l2/v4l2-input.c at v4l2_settings_changed, especially the framerate comparison and the v4l2_framerate_list value it uses. Verify that changing zoom or focus does not trigger v4l2_terminate and v4l2_init when the framerate is unchanged, then test the control adjustment with the affected USB3 webcam.