Read the number of channels from the 'dac3' tag for AC-3 in MP4.

Originally committed as revision 25054 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mov.c

@@ -559,6 +559,21 @@ static int mov_read_esds(MOVContext *c, ByteIOContext *pb, MOVAtom atom)
     return ff_mov_read_esds(c->fc, pb, atom);
 }
 
+static int mov_read_dac3(MOVContext *c, ByteIOContext *pb, MOVAtom atom)
+{
+    AVStream *st;
+    int ac3info, acmod, lfeon;
+
+    st = c->fc->streams[c->fc->nb_streams-1];
+
+    ac3info = get_be24(pb);
+    acmod = (ac3info >> 11) & 0x7;
+    lfeon = (ac3info >> 10) & 0x1;
+    st->codec->channels = ((int[]){2,1,2,3,3,4,4,5})[acmod] + lfeon;
+
+    return 0;
+}
+
 static int mov_read_pasp(MOVContext *c, ByteIOContext *pb, MOVAtom atom)
 {
     const int num = get_be32(pb);
@@ -2245,6 +2260,7 @@ static const MOVParseTableEntry mov_default_parse_table[] = {
 { MKTAG('u','d','t','a'), mov_read_default },
 { MKTAG('w','a','v','e'), mov_read_wave },
 { MKTAG('e','s','d','s'), mov_read_esds },
+{ MKTAG('d','a','c','3'), mov_read_dac3 }, /* AC-3 info */
 { MKTAG('w','i','d','e'), mov_read_wide }, /* place holder */
 { MKTAG('c','m','o','v'), mov_read_cmov },
 { 0, NULL }