[FFmpeg-devel] [PATCH] avcodec/libx264: update notes to explain the scale chosen for ROI encoding

[Guo, Yejun]

Signed-off-by: Guo, Yejun <yejun.guo at 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++) {
-- 
2.7.4