On 29/01/2019 10:14, Guo, Yejun wrote:
> Signed-off-by: Guo, Yejun <yejun....@intel.com>
> ---
> libavcodec/libx264.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> index a3493f3..8c96728 100644
> --- a/libavcodec/libx264.c
> +++ b/libavcodec/libx264.c
> @@ -383,7 +383,9 @@ static int X264_frame(AVCodecContext *ctx, AVPacket *pkt,
> const AVFrame *frame,
> qoffset = roi->qoffset.num * 1.0f / roi->qoffset.den;
> qoffset = av_clipf(qoffset, -1.0f, 1.0f);
>
> - // 25 is a number that I think it is a possible
> proper scale value.
> + /* qp range of x264 is from 0 to 51, just choose 25
> as the scale value,
> + * so the range of final qoffset is [-25.0, 25.0].
> + */
> qoffset = qoffset * 25;
>
> for (int y = starty; y < endy; y++) {
>
I'm not understanding where this number has come from at all. Is 25 purely
arbitrary? Why does the effect vary by bit depth?
From the docs explaining the best/worst behaviour on the range, I would expect
this to map 0 to 0 and 1 to 3 + 6 * bit_depth (positive or negative).
- Mark
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