@pmshop: Printers care about pixels, not filesize...
Both files are identical resolution, only 1920x1080.
A typical photoprint would be 300dpi, or about 6"x3".
You (or your printservice) could (digitally) smear these pixels out over a bigger surface, but results may vary an will certainly be blurrier than what they see as a 'quality standard'.
I've photoshopped a lot of video-stills, with some creative filtering, you might get away with 2x or 4x the original pixel size.
A typical online printservice might accept such files (more easily) for bigger prints.(Don't feel like there is much human review there.)
You could get away with some pretty low-dpi prints if used as posters since you typicaly are looking at them from a bigger distance. Guess it depends on the subject also.
I feel, looking at your samples; the second one would seem to lend itself to quite a big blowup, if it weren't for a few artifacts just around the bird (which just happens to be the main subject
).
If you're dead-set on big prints, might be worth to check out a smaller printshop, they might be a bit more flexible ?
My 2c...
Oh, and I don't think there's a way to take photographs during filming
