[MEncoder-users] Bits per pixel, bitrate and resolution

[Jeff Clagg]

On Fri, Jan 12, 2007 at 12:09:20PM +0100, Olivier Rolland wrote:

> The more I increase the resolution, the more bits are used and the
> more the file has the expected size even though the bpp is not
> increased. And, more important, the video looks better (or so I
> think).
> 
> This makes me feel that bpp is not that usefull for selecting the
> initial resolution.

I don't think bpp is very useful for ANYTHING:

- if you're concerned enough about quality to study minutae like bpp,
  then you should also care enough to avoid re-scaling the video if
  possible (bpp deciding resolution is usually tail wagging the dog)
- if you must have a rule of thumb, you would be better served by an
  understanding that, all else being equal, bitrate should scale in
  proportion to the SQUARE ROOT of the number of pixels
- nothing beats using your eyes

I'm sure there's a lot of room to argue details, but the upshot is that
a bpp rule isn't a good reason to downscale.