[FFmpeg-devel] lavc/libvpxenc: Deprecate lossless option

[Carl Eugen Hoyos]

2019-02-08 6:08 GMT+01:00, Gyan <ffmpeg at gyani.pro>:
>
>
> On 08-02-2019 03:31 AM, Carl Eugen Hoyos wrote:
>> .
>> No strong opinion here, I hadn't realized that -crf 0 only works with
>> newer versions.
>>
>> Can you explain why crf alone has no effect and needs -b:v 0?
>> Isn't this a bug both with libvpx and libaom?
>>
>
> With crf present but VBV params absent, VPX operates using a constrained
> Q RC mode , where the target bitrate acts as a ceiling. Since acvodec
> has a non-zero default -b of 200 kbps, this produces undesirable
> effects. If set to 0, VPX switches to constant quality.

Yes.
This looks like a bug to me.

> I do see this block though,
>
>      if (avctx->codec_id == AV_CODEC_ID_VP9 && ctx->lossless == 1) {
>          enccfg.rc_min_quantizer =
>          enccfg.rc_max_quantizer = 0;
>      } else {
>          if (avctx->qmin >= 0)
>              enccfg.rc_min_quantizer = avctx->qmin;
>          if (avctx->qmax >= 0)
>              enccfg.rc_max_quantizer = avctx->qmax;
>      }
>
>
> Looks like the quantizer range is disabled only by using the deprecated
> option, or has this changed?

Is your question "Isn't 'lossless 1' necessary for lossless encoding"?

> Also, with libvpx v1.7.0-1758, I get different results for -crf 0 -b:v
> 0  vs only -lossless 1, with the latter producing a slightly larger
> file, and its result showing a slightly larger SSIM score. Although
> neither produces a SSIM of 1, like libx264. Not truly lossless?

Please provide your input sample.

Carl Eugen