avformat/matroskaenc: Sort cues entries by pts

Currently they are ordered as-written (i.e. by increasing position);
in case av_interleaved_write_frame() is used, this is (mostly)
the same as ordered by increasing dts.
Yet the Matroska specification strongly recommends (SHOULD) that
the CuePoints be sorted by CueTime. mkvalidator warns when they are
not. Therefore this commit sorts them accordingly.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/matroskaenc.c

@@ -533,6 +533,7 @@ static int mkv_add_cuepoint(MatroskaMuxContext *mkv, int stream, int64_t ts,
 {
     mkv_cues *cues = &mkv->cues;
     mkv_cuepoint *entries = cues->entries;
+    unsigned idx = cues->num_entries;
 
     if (ts < 0)
         return 0;
@@ -542,11 +543,19 @@ static int mkv_add_cuepoint(MatroskaMuxContext *mkv, int stream, int64_t ts,
         return AVERROR(ENOMEM);
     cues->entries = entries;
 
-    cues->entries[cues->num_entries].pts           = ts;
-    cues->entries[cues->num_entries].stream_idx    = stream;
-    cues->entries[cues->num_entries].cluster_pos   = cluster_pos - mkv->segment_offset;
-    cues->entries[cues->num_entries].relative_pos  = relative_pos;
-    cues->entries[cues->num_entries++].duration    = duration;
+    /* Make sure the cues entries are sorted by pts. */
+    while (idx > 0 && entries[idx - 1].pts > ts)
+        idx--;
+    memmove(&entries[idx + 1], &entries[idx],
+            (cues->num_entries - idx) * sizeof(entries[0]));
+
+    entries[idx].pts           = ts;
+    entries[idx].stream_idx    = stream;
+    entries[idx].cluster_pos   = cluster_pos - mkv->segment_offset;
+    entries[idx].relative_pos  = relative_pos;
+    entries[idx].duration      = duration;
+
+    cues->num_entries++;
 
     return 0;
 }