[FFmpeg-trac] #7268(undetermined:new): ffmpeg-vaapi hevc vbr encode can not control the output bitrate

[FFmpeg]

#7268: ffmpeg-vaapi hevc vbr encode can not control the output bitrate
-------------------------------------+-------------------------------------
             Reporter:  focusluo     |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 ffmpeg -hwaccel vaapi -vaapi_device /dev/dri/renderD128 -v verbose -f
 rawvideo -s:v 1920x1080 -i ./1080p_blue_sky.yuv -vf format=nv12,hwupload
 -c:v hevc_vaapi -g 12 -bf 0 -b:v 4M -quality 4 -y
 ./hevce_vbr_1920x1080_gop12_refdist0_bitrate4M.h265

 My input is 4M bitrate, but the output is bitrate=3480.3kbits/s, which is
 out of the 10% range

 some log of output:
 [hevc_vaapi @ 0x5654f5b96240] Input 1920x1080 -> Surface 1920x1088 -> CTU
 60x34.
 Output #0, hevc, to './hevce_vbr_1920x1080_gop12_refdist0_bitrate4M.h265':
   Metadata:
     encoder         : Lavf58.17.100
     Stream #0:0: Video: hevc (hevc_vaapi) (Main), 1 reference frame,
 vaapi_vld, 1920x1080, q=2-31, 4000 kb/s, 25 fps, 25 tbn, 25 tbc
     Metadata:
       encoder         : Lavc58.20.101 hevc_vaapi
 No more output streams to write to, finishing.e=00:00:07.92
 bitrate=3442.3kbits/s speed=3.12x
 frame=  217 fps= 78 q=-0.0 Lsize=    3688kB time=00:00:08.68
 bitrate=3480.3kbits/s speed=3.11x
 video:3688kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 0.000000%
 Input file #0
 (/root/media_streams//encoderbitstreams//1080p_blue_sky.yuv):
   Input stream #0:0 (video): 217 packets read (674956800 bytes); 217
 frames decoded;
   Total: 217 packets (674956800 bytes) demuxed
 Output file #0 (./hevce_vbr_1920x1080_gop12_refdist0_bitrate4M.h265):
   Output stream #0:0 (video): 217 frames encoded; 217 packets muxed
 (3776077 bytes);
   Total: 217 packets (3776077 bytes) muxed

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Ticket URL: <https://trac.ffmpeg.org/ticket/7268>
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