in this case, v. mp4 is the video it just analysed and is trying to analyse again and failing with this error. Video shooters.... MP4 or MOV files... and why? - Facebook

They generally offer high compression with a good balance between file size and quality.

To give you a more detailed write-up, could you please tell me:

The study investigates the video compression techniques and the "opaque nature" of algorithms used by different devices to produce these files. 3. Media Testing/FFmpeg Data (Chromium)