lavf/qsvvpp: bypass vpp if not needed.

Currently vpp pipeline is always created, even for the unnecessary
cases such as setting the option "vpp_qsv=w=1280:h=720" for an input
with native resolution 1280x720. Thus introduces unnecessary performance
dropping, so bypass vpp if not needed.
Signed-off-by: Zhong Li <zhong.li@intel.com>
Signed-off-by: Maxym Dmytrychenko <maxim.d33@gmail.com>

libavfilter/vf_vpp_qsv.c

@@ -27,6 +27,7 @@
 #include "libavutil/eval.h"
 #include "libavutil/avassert.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/mathematics.h"
 
 #include "formats.h"
 #include "internal.h"
@@ -249,6 +250,7 @@ static int config_output(AVFilterLink *outlink)
     QSVVPPParam     param = { NULL };
     QSVVPPCrop      crop  = { 0 };
     mfxExtBuffer    *ext_buf[ENH_FILTERS_COUNT];
+    AVFilterLink    *inlink = ctx->inputs[0];
 
     outlink->w          = vpp->out_width;
     outlink->h          = vpp->out_height;
@@ -320,14 +322,34 @@ static int config_output(AVFilterLink *outlink)
         param.ext_buf[param.num_ext_buf++] = (mfxExtBuffer*)&vpp->procamp_conf;
     }
 
-    return ff_qsvvpp_create(ctx, &vpp->qsv, &param);
+    if (vpp->use_frc || vpp->use_crop || vpp->deinterlace || vpp->denoise ||
+        vpp->detail || vpp->procamp || inlink->w != outlink->w || inlink->h != outlink->h)
+        return ff_qsvvpp_create(ctx, &vpp->qsv, &param);
+    else {
+        av_log(ctx, AV_LOG_VERBOSE, "qsv vpp pass through mode.\n");
+        if (inlink->hw_frames_ctx)
+            outlink->hw_frames_ctx = av_buffer_ref(inlink->hw_frames_ctx);
+    }
+
+    return 0;
 }
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *picref)
 {
-    VPPContext *vpp = inlink->dst->priv;
+    int              ret = 0;
+    AVFilterContext  *ctx = inlink->dst;
+    VPPContext       *vpp = inlink->dst->priv;
+    AVFilterLink     *outlink = ctx->outputs[0];
+
+    if (vpp->qsv)
+        ret = ff_qsvvpp_filter_frame(vpp->qsv, inlink, picref);
+    else {
+        if (picref->pts != AV_NOPTS_VALUE)
+            picref->pts = av_rescale_q(picref->pts, inlink->time_base, outlink->time_base);
+        ret = ff_filter_frame(outlink, picref);
+    }
 
-    return ff_qsvvpp_filter_frame(vpp->qsv, inlink, picref);
+    return ret;
 }
 
 static int query_formats(AVFilterContext *ctx)