Re: [FFmpeg-devel] [PATCH] Allow to modify max qp configuration parameter in libvpx without reseting the encoder

[Lynne <dev@lynne.ee>]

16 Mar 2022, 13:13 by danilchap-at-google.com@ffmpeg.org:

> On Mon, Mar 14, 2022 at 4:28 PM Jan Ekström <jeebjp@gmail.com> wrote:
>
>>
>> On Mon, Mar 14, 2022 at 3:05 PM Danil Chapovalov
>> <danilchap-at-google.com@ffmpeg.org> wrote:
>> >
>> > ---
>>
>> Probably something a la
>>
>> avcodec/libvpxenc: enable dynamic quantizer reconfiguration
>>
>> ?
>>
>
> Thank you, resubmitted with new title
>
>>
>> >  libavcodec/libvpxenc.c | 7 +++++++
>> >  1 file changed, 7 insertions(+)
>> >
>> > diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
>> > index 8f94ba15dc..45baeed435 100644
>> > --- a/libavcodec/libvpxenc.c
>> > +++ b/libavcodec/libvpxenc.c
>> > @@ -1658,6 +1658,13 @@ static int vpx_encode(AVCodecContext *avctx, AVPacket *pkt,
>> >                  flags |= strtoul(en->value, NULL, 10);
>> >              }
>> >
>> > +            en = av_dict_get(frame->metadata, "max-quantizer", NULL, 0);
>> > +            if (en) {
>> > +                struct vpx_codec_enc_cfg cfg = *enccfg;
>> > +                cfg.rc_max_quantizer = strtoul(en->value, NULL, 10);
>> > +                vpx_codec_enc_config_set(&ctx->encoder, &cfg);
>> > +            }
>> > +
>>
>> There is side data already defined for quantizers, AVVideoEncParams /
>> AV_FRAME_DATA_VIDEO_ENC_PARAMS .
>>
>> In other words, this should be handled in a similar manner to ROI, not
>> as an ad-hoc metadata key in the AVFrame.
>>
>
> I've checked struct AVVideoEncParams, it doesn't look fitting: it
> contains exact qp (plus qp per plane), while my patch suggests
> changing max-qp limit for current and following frames.
> AVVideoEncParams also has some extra fields that I'm unsure how to
> handle (they are unrelated to what I'm trying to do),
> I haven't found any other struct that would contain something like max qp.
> What is ROI? What code can I use as an example of your suggestion?
>

If the encoder is operating under bitrate mode, then I think it would
be fine to interpret the qp field as a max qp field.
IIRC Youtube run libvpx and libaom under constant bitrate mode and
adjust the max quantizer per frame, because no one can fix the
rate control system of either library.
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