lavc/qsvenc: enable hevc gpb option

GPB is the default type, just contains forward references but the
slice_type is B slice with higher encoding efficiency than regular P
slice, but lower performance.

Add an option to allow user to set regular P slice.

Fix ticket#6870

Test data on Intel Kabylake (i7-7567U CPU @ 3.50GHz):
1. ffmpeg -hwaccel qsv -c:v h264_qsv -i bbb_sunflower_1080p_30fps_normal.mp4 -vsync passthrough
-vframes 1000  -c:v hevc_qsv -gpb 0 -bf 0 -q 25 test_gpb_off_bf0_kbl.mp4

transcoding fps: 85
encoded file size of test_gpb_off_bf0_kbl.mp4: 21960100 (bytes)

2. ffmpeg -hwaccel qsv -c:v h264_qsv -i bbb_sunflower_1080p_30fps_normal.mp4 -vsync passthrough
-vframes 1000  -c:v hevc_qsv -gpb 1 -bf 0 -q 25 test_gpb_on_bf0_kbl.mp4

transcoding fps: 79
encoded file size oftest_gpb_on_bf0_kbl.mp4:  21211449 (bytes)

In this case, enable gpb can bring about 7% performance drop but 3.4% encoding efficiency improvment.

Signed-off-by: Zhong Li <zhong.li@intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/libavcodec/qsvenc_hevc.c b/libavcodec/qsvenc_hevc.c
index 4c2592355e..da64b4c21b 100644
--- a/libavcodec/qsvenc_hevc.c
+++ b/libavcodec/qsvenc_hevc.c
@@ -241,6 +241,8 @@ static const AVOption options[] = {
     { "main10",  NULL, 0, AV_OPT_TYPE_CONST, { .i64 = MFX_PROFILE_HEVC_MAIN10  }, INT_MIN, INT_MAX,     VE, "profile" },
     { "mainsp",  NULL, 0, AV_OPT_TYPE_CONST, { .i64 = MFX_PROFILE_HEVC_MAINSP  }, INT_MIN, INT_MAX,     VE, "profile" },
 
+    { "gpb", "1: GPB (generalized P/B frame); 0: regular P frame", OFFSET(qsv.gpb), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, VE},
+
     { NULL },
 };