[MPlayer-users] 3 pass encoding: scaling and bitrate

[The Wanderer]

Marcos Dione wrote:

> On Tue, May 04, 2004 at 05:48:00PM -0400, D Richard Felker III wrote:
> 
>> Huh?? Does downscaling change the length of the movie in time? Does
>> it change the number of bits on a cd??? If the answer to these
>> questions is no (and it is!) how the hell do you expect downscaling
>> to let you increase the bitrate???
> 
> i thought, and excuse my ignorance here, that scaling from 720x480 to
> 640x416 (or similar) would use less 'bits per frame' (note the
> quotes), so the movie at a certain bitrate would occupy less @ the
> second size, so letting me bumping the bitrate a little to fit again
> the cd size.

I started to write a response much like this, but realized in the middle
what mistake I'd made.

Scaling from 720x480 to 640x416 will either use fewer bits per frame,
and hence lower the final bitrate, *or* result in a higher final quality
but use the same overall bitrate. If you both scale down *and* decrease
the bitrate to maintain the same quality as at the larger size, you will
have room to increase the bitrate - but a given bitrate X a given length
will always result in the same filesize. The only difference resolution
makes is what quality can be obtained with that bitrate.

-- 
       The Wanderer

Warning: Simply because I argue an issue does not mean I agree with any
side of it.

A government exists to serve its citizens, not to control them.