If it looks like a duck, walks and quacks like a duck, it must be the same duck, right? Well, no
They could be 2 different ducks. The point I'm trying to make is just because they both record in mpg doesn't mean they're using the same version of the codec or the same settings. I would open both files in
gspot (I wouldn't trust this site too much, I just used it as an example of the program) and compare them.