[OBS 28.01/macOS M1] Stinger track matte transition lags

Operating System Info

macOS 12

Other OS

No response

OBS Studio Version

28.0.1

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/sBVbRFECCov6jbaw

OBS Studio Crash Log URL

No response

Expected Behavior

The stinger transition with track matte runs smooth and finishes within 3 seconds (length of video). Scene is changing accordingly.

Current Behavior

The stinger track matte transition is very slow. After 3 seconds the track matte is only about half way animated. After the 3 seconds the track matte video is cut and the scenes are just switching, like a cut transition.

Steps to Reproduce

1. Use a QuickTime formatted, HQX typed, Grass Valley encoded, 3840x1080 track matte video file with alpha channel
2. Configure OBS to use this file as stinger transition with track matte (side-by-side)
3. Hardware encoder on / off doesn't matter
4. Do a scene switch with the stinger transition activated
5. The transition runs very slow and gets cut off when the video expires

Anything else we should know?

I was using the same stinger video on OBS 27.2.4 on the same machine before and is was working well. I notice that the CPU load goes over 110 % when the transition is running. I'm working on a macBook Pro M1 MAX.

Transition is working smooth if the stinger video has no alpha channel.

UPDATE: Works when I use ffmpeg to convert the .mov to .webm.

Start by reviewing the linked OBS log and reproducing the transition with the specified QuickTime/HQX/Grass Valley alpha video on macOS 12 and an M1 Max. Compare it with the working WebM conversion and the no-alpha case; done means the original alpha-containing stinger completes smoothly within its three-second duration instead of being cut off.