avutil/pixfmt: Clarify DV example comments for AVChromaLocation

Signed-off-by: Tim Nicholson <tim.nicholson@bbc.co.uk>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/pixfmt.h

@@ -546,7 +546,7 @@ enum AVChromaLocation {
     AVCHROMA_LOC_UNSPECIFIED = 0,
     AVCHROMA_LOC_LEFT        = 1, ///< mpeg2/4 4:2:0, h264 default for 4:2:0
     AVCHROMA_LOC_CENTER      = 2, ///< mpeg1 4:2:0, jpeg 4:2:0, h263 4:2:0
-    AVCHROMA_LOC_TOPLEFT     = 3, ///< DV
+    AVCHROMA_LOC_TOPLEFT     = 3, ///< ITU-R 601, SMPTE 274M 296M S314M(DV 4:1:1), mpeg2 4:2:2
     AVCHROMA_LOC_TOP         = 4,
     AVCHROMA_LOC_BOTTOMLEFT  = 5,
     AVCHROMA_LOC_BOTTOM      = 6,