"Cover.mp4" is a common placeholder or filename used by developers for a background video or a video used as a "hero" element on a website or splash screen.

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.

It is a generic filename often used by artists or creators for a video cover of a song (e.g., "Misty Cover.mp4").

When you record a video with enabled on a compatible Google Pixel device, your phone doesn't just create one file. Instead, it creates a "dual-file" system to balance immediate usability with high-end processing:

While it could refer to any of these, I am providing a text focused on the context, as it is a specific technical term associated with that filename. Understanding COVER.mp4 in Google Pixel Video Boost

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.

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.