A non-hidden video get decoded by CPU/GPU and blocks its bandwidth. Hidden videos don't consume any CPU/GPU. So keep them hidden until needed, and hide them again if not needed anymore.
Note that the video resolution here is 4096x2048 and NOT 3840x2160 (true 4k). This is because for 3D processing both width and height are upscaled internally to the nearest power of 2.
For 3840x2160, this upscales to 4096x4096, which is too high for current renderers.
Before uploading any videos to the GMetri File Manager (by dragging and dropping files onto it), just run them through a compression tool to reduce their sizes drastically.
Compressing a video using Handbrake
Alternatively, you can compress/resize content on the Adobe Suite
If you are using Adobe Premiere Pro or Adobe After Effects, directly compress and export the video from Adobe Media Encoder.
Here's a tutorial for this:
Compressing a Video using Media Encoder
On Mobile devices a Click action is required in the rule that starts a video (as opposed to any other event like a variable reaching a value, or the scene loading). This is because Mobile devices are strict about getting a user interaction before allowing audio to play.
Here's an example where click events are used to play a video.
A rule where click event(s) are used to play a video
Note that this restriction doesn't apply on muted videos. If you mute your video, you can play your video with any rule.
You can mute a video like this:
Muting a Video