Fix frame height vs field height confusion in MXF decoding.

Reviewed-by: Tomas Härdin <tomas.hardin@codemill.se>
Reveiwed-by: Baptiste Coudurier <baptiste.coudurier@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mxf.h

@@ -46,6 +46,14 @@ enum MXFMetadataSetType {
     TypeBottom,// add metadata type before this
 };
 
+enum MXFFrameLayout {
+    FullFrame = 0,
+    MixedFields,
+    OneField,
+    SegmentedFrame,
+    SeparateFields
+};
+
 typedef struct {
     UID key;
     int64_t offset;

libavformat/mxfdec.c

@@ -142,7 +142,8 @@ typedef struct {
     AVRational sample_rate;
     AVRational aspect_ratio;
     int width;
-    int height;
+    int height; /* Field height, not frame height */
+    int frame_layout; /* See MXFFrameLayout enum */
     int channels;
     int bits_per_sample;
     unsigned int component_depth;
@@ -832,6 +833,9 @@ static int mxf_read_generic_descriptor(void *arg, AVIOContext *pb, int tag, int
     case 0x3202:
         descriptor->height = avio_rb32(pb);
         break;
+    case 0x320C:
+        descriptor->frame_layout = avio_r8(pb);
+        break;
     case 0x320E:
         descriptor->aspect_ratio.num = avio_rb32(pb);
         descriptor->aspect_ratio.den = avio_rb32(pb);
@@ -1493,7 +1497,26 @@ static int mxf_parse_structural_metadata(MXFContext *mxf)
             if (st->codec->codec_id == CODEC_ID_NONE)
                 st->codec->codec_id = container_ul->id;
             st->codec->width = descriptor->width;
-            st->codec->height = descriptor->height;
+            st->codec->height = descriptor->height; /* Field height, not frame height */
+            switch (descriptor->frame_layout) {
+                case SegmentedFrame:
+                    /* This one is a weird layout I don't fully understand. */
+                    av_log(mxf->fc, AV_LOG_INFO, "SegmentedFrame layout isn't currently supported\n");
+                    break;
+                case FullFrame:
+                    break;
+                case OneField:
+                    /* Every other line is stored and needs to be duplicated. */
+                    av_log(mxf->fc, AV_LOG_INFO, "OneField frame layout isn't currently supported\n");
+                    break; /* The correct thing to do here is fall through, but by breaking we might be
+                              able to decode some streams at half the vertical resolution, rather than not al all.
+                              It's also for compatibility with the old behavior. */
+                case SeparateFields:
+                case MixedFields:
+                    st->codec->height *= 2; /* Turn field height into frame height. */
+                default:
+                    av_log(mxf->fc, AV_LOG_INFO, "Unknown frame layout type: %d\n", descriptor->frame_layout);
+            }
             if (st->codec->codec_id == CODEC_ID_RAWVIDEO) {
                 st->codec->pix_fmt = descriptor->pix_fmt;
                 if (st->codec->pix_fmt == PIX_FMT_NONE) {