[FFmpeg-devel] [PATCH 01/10] lavc/libopenh264enc: Add default qmin/qmax support

[Anton Khirnov]

Quoting Linjie Fu (2020-04-06 13:14:44)
> Set default QP range to (1, 51) instead of (2, 32).
> 
> QP = 0 is not well supported currently in libopenh264. If iMaxQp/iMinQp
> equals 0, the QP range would be changed unexpectedly inside libopenh264
> with a warning:
> 
> Warning:Change QP Range from(0,51) to (12,42)
> 
> [1] <https://github.com/cisco/openh264/blob/master/codec/encoder/core/src/encoder_ext.cpp#L375>
> [2] <https://github.com/cisco/openh264/issues/3259>
> 
> Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> ---
>  libavcodec/libopenh264enc.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/libavcodec/libopenh264enc.c b/libavcodec/libopenh264enc.c
> index ae6d17c..364926f 100644
> --- a/libavcodec/libopenh264enc.c
> +++ b/libavcodec/libopenh264enc.c
> @@ -135,6 +135,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
>      param.iTargetBitrate             = avctx->bit_rate;
>      param.iMaxBitrate                = FFMAX(avctx->rc_max_rate, avctx->bit_rate);
>      param.iRCMode                    = RC_QUALITY_MODE;
> +    // QP = 0 is not well supported, so default to (1, 51)
> +    param.iMaxQp                     = avctx->qmax >= 0 ? av_clip(avctx->qmax, 1, 51) : 51;
> +    param.iMinQp                     = avctx->qmin >= 0 ? av_clip(avctx->qmin, 1, param.iMaxQp) : 1;

Should we set them at all if they are not specified by the user?
Wouldn't it be better to leave the unset, as is done now?

-- 
Anton Khirnov