Some web players use a 920x516 resolution. This maintains a roughly 16:9 aspect ratio suitable for many online platforms.
If you are converting physical film to MP4 using a device like the KODAK REELS Film Digitizer Go to product viewer dialog for this item. 516 mp4
If you have a file named 516.mp4 and need to manage it, these are the standard procedures: Some web players use a 920x516 resolution