[x264-devel] Re: no gain in 2PASS for very low bitrates

[Guillaume POIRIER]

Hi,

On 12/25/05, Robert Swain <robert.swain at gmail.com> wrote:
> Hey,
>
> On 12/25/05, Guillaume POIRIER <poirierg at gmail.com> wrote:
> > Hi,
> > On 12/25/05, Patrick Lefevre <pat at wischip.com> wrote:
> > > I have used 10,000 frames content (with bunch of scene changes) @ 30fps
> > > in 2 pass mode. 1080p is still excellent quality down to 2Mb (4Mb peak).
> > > What is considered low bit-rate?]. For playback, I used mplayer,
> > > otherwise the decoding filter appears too slow (?), at least if used
> > > with mediaplayer. [1221 snapshot]
> >
> > My definition low low bitrate is when you encode a DVD size video with
> > a bit per pixel ratio lower than 0.9 with a H.264 codec. Some ppl
> > won't agree with that as it widely depends on what kind of quality you
> > target.
>
> I think you mean 0.09 bpp. :) But of course we both know that's a
> rough estimate and the requirement varies based on content. Consider
> it a guideline for 'an average DVD' as your source.

Woops, that's what I meant, yes! Bit per pixel is a pretty rough
estimate as not only the quality you'll get depends on the source (if
it compresses well or not) but also on video resolution, i.e. lower
resolution need a respectively bigger bpp to look good than higher
resolution videos.
Therefore, once you'd have read some video encoding guides, you should
just use bpp as a starting point to run a compression test, and then
adjust the bitrate accordingly.

Guillaume
--
Life is pleasant. Death is peaceful. It's the transition that's troublesome.
    Isaac Asimov (1920 - 1992)

MPlayer's doc is offline. Find some fresh one here:
http://tuxrip.free.fr//MPlayer-DOCS-HTML/en/
http://tuxrip.free.fr//MPlayer-DOCS-HTML/fr/

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