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>

libavcodec/qsvenc.c

@@ -267,6 +267,11 @@ static void dump_video_param(AVCodecContext *avctx, QSVEncContext *q,
 #endif
 #endif
 
+#if QSV_HAVE_GPB
+    if (avctx->codec_id == AV_CODEC_ID_HEVC)
+        av_log(avctx, AV_LOG_VERBOSE,"GPB: %s\n", print_threestate(co3->GPB));
+#endif
+
     if (avctx->codec_id == AV_CODEC_ID_H264) {
         av_log(avctx, AV_LOG_VERBOSE, "Entropy coding: %s; MaxDecFrameBuffering: %"PRIu16"\n",
                co->CAVLC == MFX_CODINGOPTION_ON ? "CAVLC" : "CABAC", co->MaxDecFrameBuffering);
@@ -748,6 +753,10 @@ FF_ENABLE_DEPRECATION_WARNINGS
 #if QSV_HAVE_CO3
         q->extco3.Header.BufferId      = MFX_EXTBUFF_CODING_OPTION3;
         q->extco3.Header.BufferSz      = sizeof(q->extco3);
+#if QSV_HAVE_GPB
+        if (avctx->codec_id == AV_CODEC_ID_HEVC)
+            q->extco3.GPB              = q->gpb ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
+#endif
         q->extparam_internal[q->nb_extparam_internal++] = (mfxExtBuffer *)&q->extco3;
 #endif
     }

libavcodec/qsvenc.h

@@ -47,6 +47,8 @@
 #define QSV_HAVE_LA_HRD QSV_VERSION_ATLEAST(1, 11)
 #define QSV_HAVE_VDENC  QSV_VERSION_ATLEAST(1, 15)
 
+#define QSV_HAVE_GPB    QSV_VERSION_ATLEAST(1, 18)
+
 #if defined(_WIN32) || defined(__CYGWIN__)
 #define QSV_HAVE_AVBR   QSV_VERSION_ATLEAST(1, 3)
 #define QSV_HAVE_ICQ    QSV_VERSION_ATLEAST(1, 8)
@@ -173,6 +175,7 @@ typedef struct QSVEncContext {
 
     int repeat_pps;
     int low_power;
+    int gpb;
 
     int a53_cc;
 

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 },
 };