If you try to share the video before processing is finished, you are usually sharing the COVER.mp4 preview.
This is a massive, unprocessed file (often 1GB for every 30 seconds of 4K footage). This file contains the high-dynamic-range data that Google's servers use to "boost" the video's lighting, stabilization, and color. How the Process Works: Upload: Google Photos uploads both files to the cloud. Processing: The "Boost" happens on Google's servers. Cover.mp4
It is a generic filename often used by artists or creators for a video cover of a song (e.g., "Misty Cover.mp4"). If you try to share the video before
When using the Video Boost feature on Pixel phones, the device generates a temporary file named COVER.mp4 . This is a low-resolution (1080p) preview that you can view immediately while the high-quality version is being processed in the cloud. How the Process Works: Upload: Google Photos uploads
Once the boosted version is ready, Google Photos downloads the final high-quality version and typically deletes the massive raw MAIN.mp4 to save space.
Users often find these files when manually backing up their phones or using third-party file managers. If you see a COVER.mp4 file and notice it looks lower quality than expected, it simply means the "Boost" hasn't finished processing or syncing yet.
Did you want to know more about this feature, or were you looking for a script to implement a background video named "cover.mp4" on a website? One of my favourite music quotes! | Nick Higgs The Singer