[MPlayer-users] non-mod16 resolutions
Matthew W. Miller
mwmiller at columbus.rr.com
Thu Sep 16 03:43:17 CEST 2004
On Wed, Sep 15, 2004 at 04:37:36AM -0400, D Richard Felker III wrote:
>On Wed, Sep 15, 2004 at 08:42:25AM +0100, Martin Collins wrote:
>> Interesting that the bitrate increases linearly with the resolution
>> rather than as the square as one would (naiively) expect.
>yes, very interesting since i hypothesized this in the draft encoding
>guide, i.e. that bits_per_pixel should not be used, but instead
>bits_squared_per_pixel, for the purpose of scaling image size versus
>quality. it's nice to see it backed up by data.
Okay. In DOCS/tech/encoding-tips.txt Mosu suggests the formula
bpp = (vbitrate * 1000) / (width * height * fps)
or to solve for vbitrate,
vbitrate = bpp * width * height * fps / 1000
So if I'm reading Loren and Martin and Rich (oh my!)'s findings here, a
better formula would be
vbitrate = bpsp * sqrt(width * height) * fps / 1000
where bpsp is the desired Bits Per Square root of Pixel-count.
Note that this calculates vbitrate in kbit/sec. To calculate it in
bit/sec, leave out the "/ 1000". Of course, MPlayer will make an
educated guess about which one you're using. :)
Is anyone feeling daring enough to throw out a few approximately 'good
enough' bpsp levels?
Of course "You're going about this all wrong, the bitrate to use depends
on what you need for a particular movie" is a perfectly acceptable
response as well.
Matthew Miller <mwmiller at columbus.rr.com>
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