From the Heresphere dev:

@everyone HereSphere update v0.12.0 is now available Meta Quest devices on the Meta App Store RC channel and itch.io. This update adds support for external alpha videos for passthrough and audio track switching.

External Alpha:

Separate videos can be used to control the opacity of a passthrough video. Black areas of the video will have no opacity (transparent), while colored portions of the video will be opaque. The final opacity is the sum of all color channels (RGB in linear color space). If generating your own alpha videos, 480p seems sufficient for the resolution. Make sure to match the keyframe spacing of the original video to keep seeks aligned.
Name the external alpha video the same as the original video, but place "_XALPHA" at the end of the name right before the video extension.
If a matching "_XALPHA" video is detected, an eye symbol will appear near the upper left corner of the seekbar. Click on it to switch between external alpha passthrough and no passthrough. You can also change the mask type to "Alpha External" in the advanced video settings under the "Environment" group.
If using the HereSphere web API, external alpha videos can be provided using the "alphaExternal" field, which is a string with the url of the external alpha video.
An eye icon will appear near the top left of the web API thumbnail if an external alpha video url is provided for that scene.

Audio Tracks:

If a video has multiple audio tracks, a drop down box will appear above the seekbar. Switch between the audio tracks by using the drop down box. Currently, the player can only switch between tracks if the labeled languages are different.

Other Changes:

Default opacity multiplier is increased to 2.0
The encoding and resolution drop down boxes are now properly hidden when not streaming from the HereSphere web API

What does this mean? Will SLR jump on board and take advantage of this? Or will individuals need to produce their own external alpha for videos? I heard rumor that Czech VR may release a few external alphas soon. I’ll be curious to try it out!