movenc: Keep track of the allocated size for the cluster array

When writing fragmented mp4, the cluster array is reset when a
fragment is written. Instead of starting off reallocating the
array only based on the number of current elements in it, keep
track of how many elements there were allocated earlier.

This avoids reallocating this array needlessly when writing
fragmented mp4 files.

Bug-Id: 525
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/movenc.c

@@ -2869,10 +2869,12 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
         memcpy(trk->vos_data, pkt->data, size);
     }
 
-    if (!(trk->entry % MOV_INDEX_CLUSTER_SIZE)) {
-        trk->cluster = av_realloc(trk->cluster, (trk->entry + MOV_INDEX_CLUSTER_SIZE) * sizeof(*trk->cluster));
-        if (!trk->cluster)
-            return -1;
+    if (trk->entry >= trk->cluster_capacity) {
+        unsigned new_capacity = trk->entry + MOV_INDEX_CLUSTER_SIZE;
+        if (av_reallocp_array(&trk->cluster, new_capacity,
+                              sizeof(*trk->cluster)))
+            return AVERROR(ENOMEM);
+        trk->cluster_capacity = new_capacity;
     }
 
     trk->cluster[trk->entry].pos = avio_tell(pb) - size;

libavformat/movenc.h

@@ -93,6 +93,7 @@ typedef struct MOVTrack {
     int         vos_len;
     uint8_t     *vos_data;
     MOVIentry   *cluster;
+    unsigned    cluster_capacity;
     int         audio_vbr;
     int         height; ///< active picture (w/o VBI) height for D-10/IMX
     uint32_t    tref_tag;