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

["Tomas Härdin" <git@haerdin.se>]

mån 2024-01-22 klockan 15:59 +0200 skrev Martin Storsjö:
> 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.

Ooh, didn't know that. That sounds like a decent solution here. Can RoQ
really not do < 800 kbps at all or is it just that it looks bad with
say 256x256 but perhaps more decent with 128x128 or so?

/Tomas
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