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

[Guillaume POIRIER]

Hi,

On 1/12/07, Jeff Clagg <snacky at ikaruga.co.uk> wrote:
> 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.

Though I agree with your statement, don't know how I could easily
adapt it to existing doc.

As you can see here:
http://www1.mplayerhq.hu/DOCS/HTML/en/menc-feat-dvd-mpeg4.html#menc-feat-dvd-mpeg4-resolution-bitrate-compute
the doc already uses the bit per pixel metric.

Do you have any suggestion on how to use a better metric which could
both fit in this paragraph, and be understandable by the user?

Guillaume