OBS has added a new feature for Track Matte transitions. These are essentially a video mask and a transition placed into a single file instead of multiple different files.
Matte Transitions Setup:
1. First off we're going to start by heading to OBS and adding in a "Stinger" transition at the bottom right
2. Once you've added you're selected "Stinger" go ahead and click on the cogwheel and click properties, this will open up a bunch of settings for you.
3. When the properties first open, you'll want to make sure that Track Matte is enabled, this will uncover some new options for you. You'll want to make sure "Same file, side-by-side (stinger on the left, track matte on the right)" is selected
4. Next up let's get your transition added in. At the top of your transition settings there will be a "Browse" button, go ahead and click that and browse for your transition file.
5. Final callout is to ensure that the "Audio Transition Point Type" is set to frame and ensure that the Transition Point itself is set to 75 frames.
Matte Transition Settings:
Transition Type: Time (Frame)
Transition Points: 75