Question about MPEG-2 file sizes

S Vid wrote on 1/15/2012, 8:47 PM

I have 2 MPEG-2 files, both 720x480 resolution.

First:
length: 1:27:44
file size: 3.61GB
6 audio channels

Second:
length: 41:57
file size: 3.12GB
2 audio channels

Why would the second MPEG-2 file, that is about half the length of the first and that has less audio channels, be almost the same filesize as the first?

(If I "Render As" MPEG-4 using Vegas 11, the second file is [correctly] about half the filesize of the first: 456MB vs. 214MB)

Comments

Steve Grisetti wrote on 1/15/2012, 9:30 PM

MPEGs use variable compression and quality levels. You can raise or lower the bit-rate as well as the number of iFrames so that its size fits a given need.

musicvid10 wrote on 1/15/2012, 10:17 PM

"Why would the second MPEG-2 file, that is about half the length of the first and that has less audio channels, be almost the same filesize as the first?"

Because you haven't taken into account the average bitrate of either file.
MediaInfo is your friend. So is an understanding of basic math.
;?)