[MPlayer-users] mencoder: effective use of qp, crf params for x264?

[Guillaume POIRIER]

Hi,

On 1/30/07, matthew.garman at gmail.com <matthew.garman at gmail.com> wrote:
> On Mon, Jan 29, 2007 at 05:08:59PM +0100, Guillaume POIRIER wrote:
> > You can think of crf as an option to select the average quality
> > you want, qp as a constant quality mode, and "two pass" as
> > variable quality mode.
>
> Made me think of another question: there's a range given for crf
> (1--50).  Looks like the bitrate param is open-ended.  Is there any
> approximate relation between a given crf value and a specific
> bitrate?  E.g., could you say crf=25 is roughly equivalent to
> bitrate=1000, crf=10 is approximately bitrate=2000?

No.
the bitrate that will end up being used by qp will depend on the
complexity of the scene (more or less equivalent to "how well it
compresses"), and the "amount of efforts" that the codec put towards
trying to make good use of the bits.
Likewise, if you give bitrate as a target, the average quant of the
frame/the movie will depend on how well the movie compresses with the
given encoding parameters

Guillaume