mxf: Read field dominance flag

And export the information in field_order.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavformat/mxfdec.c

@@ -134,6 +134,9 @@ typedef struct {
     int width;
     int height; /* Field height, not frame height */
     int frame_layout; /* See MXFFrameLayout enum */
+#define MXF_TFF 1
+#define MXF_BFF 2
+    int field_dominance;
     int channels;
     int bits_per_sample;
     unsigned int component_depth;
@@ -830,6 +833,9 @@ static int mxf_read_generic_descriptor(void *arg, AVIOContext *pb, int tag, int
         descriptor->aspect_ratio.num = avio_rb32(pb);
         descriptor->aspect_ratio.den = avio_rb32(pb);
         break;
+    case 0x3212:
+        descriptor->field_dominance = avio_r8(pb);
+        break;
     case 0x3301:
         descriptor->component_depth = avio_rb32(pb);
         break;
@@ -1507,6 +1513,19 @@ static int mxf_parse_structural_metadata(MXFContext *mxf)
                      * It's also for compatibility with the old behavior. */
                 case SeparateFields:
                 case MixedFields:
+                    switch (descriptor->field_dominance) {
+                    case MXF_TFF:
+                        st->codec->field_order = AV_FIELD_TT;
+                        break;
+                    case MXF_BFF:
+                        st->codec->field_order = AV_FIELD_BB;
+                        break;
+                    default:
+                        avpriv_request_sample(mxf->fc,
+                                              "Field dominance %d support",
+                                              descriptor->field_dominance);
+                        break;
+                    }
                     /* Turn field height into frame height. */
                     st->codec->height *= 2;
                 default: