Re: [dvd::rip] less fps = more MBs?

Paul Hunnisett paulhunni@xxxxxxxxxxxxxxxx Mon Sep 20 22:40:59 2004 
wrote:

> All seemed to work well which was great - except that I noticed that 
> when I reduce the framerate (at first from 25 to 23 and then to 15) the 
> size of the resulting file was larger than it had been at 25fps - which 
> was the exact opposite of what I expected.

Framerate may affect filesize, but it depends on your settings.

If you set a fixed video bitrate by specifying it manually or defining 
the desired file size, framerate shouldn't matter. Video bitrate is 
"data amount per time", regardless how the other video settings are, 
they don't (should, see below ;) influence the file size, because they 
are no parameter for the file size calculation. Of course, quality is 
different (e.g. bad if the image resolution is very big, but better if 
the resolution is small - although the image gets blurry if you need to
scale it up again to fit on the screen).

But if you use dvd::rip's BPP approach the thing is different. This is 
"bits per pixel" and of course the number of image pixel depends on the
frame rate: the higher the rate, the more pixels. In that case the 
filesize should decrease with smaller framerates.

But finally the whole video encoder bitrate control stuff isn't really 
deterministic and depends a lot on the actual content. You can't 
reliably predict results from some theory due to that... ;)

Regards,

Joern

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