MPEG-4

I am less familiar with doing this kind of thing on an iPad. The problem with video is there are many, many encoding components out there. These then get bundled together in a container such as mp4 which admittedly limits some variants but some make it in. Then the app you are using to play it (and you are using an app even if it is just Apple's) has to contain a decoder for the type of audio or video you are seeing. Apple is somewhat limited, particularly with them dropping older video codecs recently (at least in iMovie they did). VLC is pretty well trusted and has the advantage that it can play pretty much anything. At least then you could see if the issue was with the payer you are using or if it is with the file itself. If it's with the player then you don't have much option since Apple doesn't let you mess with app capabilities, particularly not on a iPadOS or iOS. Then your option would be to use an app to recode to a mroe friendly version. You'd lose quality and at this stage I particularly am not familiar with how you'd do this on an iPad. Computers have a LOT more flexibility in this regard.

What is the origin of this video? It could be using a non-standard codec. Have you tried playing it with an app such as the free VLC?

Thanks for the closure. It was probably some flavor of mp4 codec that Apple didn't support. Saying something is "mp4" is a bit like saying somebody owns a "car."