Re: [FFmpeg-devel] [RFC]] swscale modernization proposal

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sat, Jul 06, 2024 at 02:11:30AM +0200, Hendrik Leppkes wrote:
> On Fri, Jul 5, 2024 at 11:34 PM Michael Niedermayer
> <michael@niedermayer.cc> wrote:
> > > /**
> > >  * The exact interpretation of these quality presets depends on the backend
> > >  * used, but the backend-invariant common settings are derived as follows:
> > >  */
> > > enum AVScaleQuality {
> > >     AV_SCALE_ULTRAFAST = 1,  /* no dither,      nearest+nearest     */
> > >     AV_SCALE_SUPERFAST = 2,  /* no dither,      bilinear+nearest    */
> > >     AV_SCALE_VERYFAST  = 3,  /* no dither,      bilinear+bilinear   */
> > >     AV_SCALE_FASTER    = 4,  /* bayer dither,   bilinear+bilinear   */
> > >     AV_SCALE_FAST      = 5,  /* bayer dither,   bicubic+bilinear    */
> > >     AV_SCALE_MEDIUM    = 6,  /* bayer dither,   bicubic+bicubic     */
> > >     AV_SCALE_SLOW      = 7,  /* bayer dither,   lanczos+bicubic     */
> > >     AV_SCALE_SLOWER    = 8,  /* full dither,    lanczos+bicubic     */
> > >     AV_SCALE_VERYSLOW  = 9,  /* full dither,    lanczos+lanczos     */
> > >     AV_SCALE_PLACEBO   = 10, /* full dither,    lanczos+lanczos     */
> >
> > I dont think its a good idea to hardcode dither and the "FIR" filter to the quality level in the API
> >
> 
> The entire point of presets is to have them provide a predefined set
> of parameters, easy for users to pick one value, rather than a bunch.
> And what a preset actually means should be documented.
> How do you define "presets" if they don't hardcode a list of choices
> for all the relevant options?
> 
> Advanced settings exist for a user to select any particular detail, if
> they so desire.

The problem is if new features are added and you have a hardcoded list in
the API what each quality corresponds to change it you have to bump major

also, do we really have or want to have optimized nearest neighbor scaler
code ?
If not the AV_SCALE_ULTRAFAST could be slower than AV_SCALE_VERYFAST
simply because it now "has to" do something we actually have not optimized

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras

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