nvenc: only write the VUI signal type fields if they are set

Based on a patch by Agatha Hu <ahu@nvidia.com>.

libavcodec/nvenc.c

@@ -588,8 +588,9 @@ static int nvenc_setup_h264_config(AVCodecContext *avctx)
     NV_ENC_CONFIG_H264 *h264               = &cc->encodeCodecConfig.h264Config;
     NV_ENC_CONFIG_H264_VUI_PARAMETERS *vui = &h264->h264VUIParameters;
 
-    vui->colourDescriptionPresentFlag = 1;
-    vui->videoSignalTypePresentFlag   = 1;
+    vui->colourDescriptionPresentFlag = avctx->colorspace      != AVCOL_SPC_UNSPECIFIED ||
+                                        avctx->color_primaries != AVCOL_PRI_UNSPECIFIED ||
+                                        avctx->color_trc       != AVCOL_TRC_UNSPECIFIED;
 
     vui->colourMatrix            = avctx->colorspace;
     vui->colourPrimaries         = avctx->color_primaries;
@@ -597,6 +598,9 @@ static int nvenc_setup_h264_config(AVCodecContext *avctx)
 
     vui->videoFullRangeFlag = avctx->color_range == AVCOL_RANGE_JPEG;
 
+    vui->videoSignalTypePresentFlag = vui->colourDescriptionPresentFlag ||
+                                      vui->videoFullRangeFlag;
+
     h264->disableSPSPPS = (avctx->flags & AV_CODEC_FLAG_GLOBAL_HEADER) ? 1 : 0;
     h264->repeatSPSPPS  = (avctx->flags & AV_CODEC_FLAG_GLOBAL_HEADER) ? 0 : 1;
     h264->outputAUD     = 1;