utvideoenc: Add support for the new BT.709 FourCCs for YCbCr

With cli usage the decoder might have not set the colorspace during
encoder init, manual colorspace override might be needed in such
cases.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/utvideoenc.c

@@ -83,7 +83,10 @@ static av_cold int utvideo_encode_init(AVCodecContext *avctx)
             return AVERROR_INVALIDDATA;
         }
         c->planes        = 3;
-        avctx->codec_tag = MKTAG('U', 'L', 'Y', '0');
+        if (avctx->colorspace == AVCOL_SPC_BT709)
+            avctx->codec_tag = MKTAG('U', 'L', 'H', '0');
+        else
+            avctx->codec_tag = MKTAG('U', 'L', 'Y', '0');
         original_format  = UTVIDEO_420;
         break;
     case AV_PIX_FMT_YUV422P:
@@ -93,7 +96,10 @@ static av_cold int utvideo_encode_init(AVCodecContext *avctx)
             return AVERROR_INVALIDDATA;
         }
         c->planes        = 3;
-        avctx->codec_tag = MKTAG('U', 'L', 'Y', '2');
+        if (avctx->colorspace == AVCOL_SPC_BT709)
+            avctx->codec_tag = MKTAG('U', 'L', 'H', '2');
+        else
+            avctx->codec_tag = MKTAG('U', 'L', 'Y', '2');
         original_format  = UTVIDEO_422;
         break;
     default: