mov: allocate the tag value dynamically

This allows to load metadata entries longer than 1024 bytes.
Displaying them is still limited to 1024 characters, but applications
can load them fully now.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/mov.c

@@ -253,10 +253,10 @@ static int mov_metadata_loci(MOVContext *c, AVIOContext *pb, unsigned len)
 static int mov_read_udta_string(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
     char tmp_key[5];
-    char str[1024], key2[32], language[4] = {0};
+    char *str, key2[32], language[4] = {0};
     const char *key = NULL;
     uint16_t langcode = 0;
-    uint32_t data_type = 0, str_size;
+    uint32_t data_type = 0, str_size, str_size_alloc;
     int (*parse)(MOVContext*, AVIOContext*, unsigned, const char*) = NULL;
 
     switch (atom.type) {
@@ -336,13 +336,17 @@ static int mov_read_udta_string(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     if (atom.size < 0)
         return AVERROR_INVALIDDATA;
 
-    str_size = FFMIN3(sizeof(str)-1, str_size, atom.size);
+    // allocate twice as much as worst-case
+    str_size_alloc = str_size * 2;
+    str = av_malloc(str_size_alloc);
+    if (!str)
+        return AVERROR(ENOMEM);
 
     if (parse)
         parse(c, pb, str_size, key);
     else {
         if (data_type == 3 || (data_type == 0 && (langcode < 0x400 || langcode == 0x7fff))) { // MAC Encoded
-            mov_read_mac_string(c, pb, str_size, str, sizeof(str));
+            mov_read_mac_string(c, pb, str_size, str, str_size_alloc);
         } else {
             avio_read(pb, str, str_size);
             str[str_size] = 0;
@@ -356,8 +360,9 @@ static int mov_read_udta_string(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     }
     av_dlog(c->fc, "lang \"%3s\" ", language);
     av_dlog(c->fc, "tag \"%s\" value \"%s\" atom \"%.4s\" %d %"PRId64"\n",
-            key, str, (char*)&atom.type, str_size, atom.size);
+            key, str, (char*)&atom.type, str_size_alloc, atom.size);
 
+    av_freep(&str);
     return 0;
 }