[FFmpeg-trac] #7629(avcodec:new): VAAPI: HEVC (h265) VBR encode bitrate way too low

FFmpeg trac at avcodec.org
Wed Dec 19 10:16:45 EET 2018

#7629: VAAPI: HEVC (h265) VBR encode bitrate way too low
             Reporter:  uartie      |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avcodec
              Version:  git-master  |               Resolution:
             Keywords:  vaapi       |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by lizhong1008):

 Took a quick look at this issue. I believe this is a i965 driver instead
 of ffmpeg issue.

 Here are the file size of encoded bitstreams via FFmpeg with same bitrate
 setting as bug description but just changing encoder type and BRC
 mode.(prefix "i965" means i965 driver, "ihd" means iHD driver)

 ls -ls test_*
 2564 -rw-r--r-- 1 root root 2624921 12月 19 15:19 test_i965_cbr.h265
 2560 -rw-r--r-- 1 root root 2621123 12月 19 15:17 test_i965.h264
 384 -rw-r--r-- 1 root root  391474 12月 19 15:19 test_i965_vbr.h265
 2556 -rw-r--r-- 1 root root 2613360 12月 19 15:19 test_ihd_cbr.h265
 2536 -rw-r--r-- 1 root root 2596236 12月 19 15:17 test_ihd.h264
 2556 -rw-r--r-- 1 root root 2617061 12月 19 15:18 test_ihd_vbr.h264
 2544 -rw-r--r-- 1 root root 2604431 12月 19 15:20 test_ihd_vbr.h265

 You can see the file size is not normal for "i965 driver + VBR mode +
 HEVC" case, any other cases are normal.

 Checked i965 driver: https://github.com/intel/intel-vaapi-
 You can find the case "target_percentage <=
 HEVC_BRC_MIN_TARGET_PERCENTAGE" hasn't been handled.
 HEVC_BRC_MIN_TARGET_PERCENTAGE is 50, but gstreamer-vaapi always set it to
 be 70 for VBR (see: https://github.com/GStreamer/gstreamer-
 vaapi/blob/master/gst-libs/gst/vaapi/gstvaapiencoder.c#L939), so this
 gstreamer-vaapi won't trigger it.

 Current setting will make target_percentage=50 in FFmpeg (see:
 and then trigger the driver issue.

 To further make sure, I have tried to set the maxrate to be 7M (then
 target_percentage is larger then 50):
 LIBVA_DRIVER_NAME=i965 ./ffmpeg -hwaccel vaapi -vaapi_device
 /dev/dri/renderD128 -v verbose -f rawvideo -pix_fmt yuv420p -s:v 1920x1080
 -r:v 30 -i /root/Videos/1080p_blue_sky.yuv -vf 'format=nv12,hwupload' -c:v
 hevc_vaapi -b:v 4000k -maxrate 7000k -vframes 150 -y

 ls -ls test_i965_maxrate7M_vbr.h265
 2626930 12月 19 15:51 test_i965_maxrate7M_vbr.h265
 echo "2626930*8*30/1024.0/150" |bc
 You can see the encoded bit-rate is close to target bit-rate.

Ticket URL: <https://trac.ffmpeg.org/ticket/7629#comment:3>
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