mov: detect cover art pictures by content

I've got some m4a samples that had jpeg cover art marked as png. Since
these files were supposedly written by iTunes, and other software can
read it (e.g. clementine does), this should be worked around.

Since png has a very simple to detect header, while it's apparently a
real pain to detect jpeg in the general case, try to detect png and
assume jpeg otherwise. Not bothering with bmp, as I have no test case.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 95dc1ee7ad..9532213023 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -200,6 +200,14 @@ static int mov_read_covr(MOVContext *c, AVIOContext *pb, int type, int len)
     if (ret < 0)
         return ret;
 
+    if (pkt.size >= 8 && id != AV_CODEC_ID_BMP) {
+        if (AV_RB64(pkt.data) == 0x89504e470d0a1a0a) {
+            id = AV_CODEC_ID_PNG;
+        } else {
+            id = AV_CODEC_ID_MJPEG;
+        }
+    }
+
     st->disposition              |= AV_DISPOSITION_ATTACHED_PIC;
 
     st->attached_pic              = pkt;