does the size of a file determine the quality of the video?
if it were an xvid/avi yes.
with x264 mp4 or mkv, no.
x264 uses a fixed quality setting (crf).
size is directly tied to the complexity of the source (i.e. still vs. moving, grainy vs sharp, solid vs.
detailed, etc.), and how much compression can be applied to any given frame and still maintain the
fixed quality setting.