Re: [FFmpeg-devel] [PATCH] liavcodec: add bit-rate support to RoQ video encoder

[Victor Luchitz <vluchits@gmail.com>]

Thanks, I will look into it

On Mon, Jan 22, 2024 at 4:59 PM Martin Storsjö <martin@martin.st> wrote:

> On Mon, 22 Jan 2024, Tomas Härdin wrote:
>
> >>> >>>  -    if (frame->quality)
> >> > > -        enc->lambda = frame->quality - 1;
> >> > > -    else
> >> > > -        enc->lambda = 2*ROQ_LAMBDA_SCALE;
> >> > > +    if (avctx->bit_rate <= ROQ_DEFAULT_MIN_BIT_RATE) {
> >> > > +        /* no specific bit rate desired, use frame quality */
> >> > > +        if (frame->quality)
> >> > > +            enc->lambda = frame->quality - 1;
> >> > > +        else
> >> > > +            enc->lambda = 2*ROQ_LAMBDA_SCALE;
> >> > > +    }
> >> >
> >> > This looks like a bit of a janky way to switch between qscale and
> >> > bitrate. Isn't there a way to detect whether an option has been set
> >> > explicitly? At the very least this behavior should be documented in
> >> > doc/encoders.texi
> >> >
> >>
> >> Originally, the code just checked for bit_rate !=
> >> AV_CODEC_DEFAULT_BITRATE,
> >> which required including options_table.h, which in turn produced a
> >> bunch
> >> of compilation warnings about certain fields being deprecated. None
> >> of the
> >> other codecs include that file + many simply check the bit_rate field
> >> against
> >> magic constants.
> >
> > grepping for 200000 didn't reveal anything like that. Do you have a
> > specific example of an encoder that does this?
> >
> > Perhaps we could move AV_CODEC_DEFAULT_BITRATE somewhere else, to avoid
> > pulling in a bunch of unrelated stuff. Maybe that doesn't need to hold
> > up this patch though. Tbh the way bitrate is defaulted to a value,
> > which makes it impossible to differentiate between a user-supplied -b
> > 200k an no -b at all, is even more janky. The default is also
> > ridiculously low..
> >
> > I know some encoders like libvpx allow specifying both quality (-crf)
> > and bitrate at the same time
>
> FWIW, it's possible for an encoder to individually override the defaults
> for fields like these. See e.g. x264_defaults in libx264.c, where it
> overrides the default bitrate to zero.
>
> // Martin
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-- 
Best regards,
 Victor Luchitz
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