mxfdec: Fix regression on files from Pinnacle Thunder

The reason for this is that such files have IndexTableSegments which when parsed
cover EditUnit ranges like this:

 [0,1)
 [249,250)
 [249,377)
 [0,249)

where each interval is [IndexStartPosition,IndexStartPosition+IndexDuration).
This would be reduced to a sparse index like:

 [0,1), [249,250)

instead of the full range:

 [0,249), [249,377)

See TimeCode_HD.mxf, UMID =
060a2b340101010101010410130000000004001aa0e59175025b2a5600da4101.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mxfdec.c

@@ -952,6 +952,7 @@ static int mxf_get_sorted_table_segments(MXFContext *mxf, int *nb_sorted_segment
     int i, j, nb_segments = 0;
     MXFIndexTableSegment **unsorted_segments;
     int last_body_sid = -1, last_index_sid = -1, last_index_start = -1;
+    uint64_t last_index_duration = 0;
 
     /* count number of segments, allocate arrays and copy unsorted segments */
     for (i = 0; i < mxf->metadata_sets_count; i++)
@@ -974,19 +975,23 @@ static int mxf_get_sorted_table_segments(MXFContext *mxf, int *nb_sorted_segment
     /* sort segments by {BodySID, IndexSID, IndexStartPosition}, remove duplicates while we're at it */
     for (i = 0; i < nb_segments; i++) {
         int best = -1, best_body_sid = -1, best_index_sid = -1, best_index_start = -1;
+        uint64_t best_index_duration = 0;
 
         for (j = 0; j < nb_segments; j++) {
             MXFIndexTableSegment *s = unsorted_segments[j];
 
             /* Require larger BosySID, IndexSID or IndexStartPosition then the previous entry. This removes duplicates.
              * We want the smallest values for the keys than what we currently have, unless this is the first such entry this time around.
+             * If we come across an entry with the same IndexStartPosition but larger IndexDuration, then we'll prefer it over the one we currently have.
              */
             if ((i == 0     || s->body_sid > last_body_sid || s->index_sid > last_index_sid || s->index_start_position > last_index_start) &&
-                (best == -1 || s->body_sid < best_body_sid || s->index_sid < best_index_sid || s->index_start_position < best_index_start)) {
+                (best == -1 || s->body_sid < best_body_sid || s->index_sid < best_index_sid || s->index_start_position < best_index_start ||
+                (s->index_start_position == best_index_start && s->index_duration > best_index_duration))) {
                 best             = j;
                 best_body_sid    = s->body_sid;
                 best_index_sid   = s->index_sid;
                 best_index_start = s->index_start_position;
+                best_index_duration = s->index_duration;
             }
         }
 
@@ -998,6 +1003,7 @@ static int mxf_get_sorted_table_segments(MXFContext *mxf, int *nb_sorted_segment
         last_body_sid    = best_body_sid;
         last_index_sid   = best_index_sid;
         last_index_start = best_index_start;
+        last_index_duration = best_index_duration;
     }
 
     av_free(unsorted_segments);