You could try a file comparison program & see if that might point out the differences between the two files.
Altap Salamander (file manager) contains a File Comparator program (Ctrl+Shift+C).
Throw two files at it & let it do its' thing.
You can (manually) select binary or text compare.
(On binary files, such as a movie, binary mode is quicker - though, depending on what they changes are, may not be an "appropriate" method of comparison.
*Appropriate.
Sometimes, an odd byte difference here or there can throw off a binary comparison that ends up making [virtually] the entire file
appear to be different, where a Text comparison will actually point out those differences. In a case like that, it is often a tag-like situation, perhaps even a version level number of an encoder used to encode the video, so something negligible. With "odd" different lengths, like you have, it could be some "dumy" bytes at the end, that while different, are "past" the "end of the file", & so are totally irrelevant. If you came across larger swaths of differences, that would have to be looked at further. If they were something like nul bytes ($00$), that could point out corruption - where one version is, & the other is not. (If that were the case, it would be odd for the file size to be different - unless the file, at some point, was recovered by some sort of "unerase" program.) Also note that "corrupt" video may
appear to be fine, as in, you may not "see" corruption, necessarily, with your player automatically bypassing corrupt spots.
So throw Salamander (or some other comparison) program at the files & see if it gives you something meaningful back.
