avformat/avidec: Workaround broken initial frame

Fixes Ticket4851

Signed-off-by: Michael Niedermayer <[email protected]>
(cherry picked from commit 3e2ef00394b8079e93835d47c993868229f07502)

Conflicts:
	libavformat/avidec.c

1 files changed, 2 insertions, 1 deletions

diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index fbbcde7dff..bf9d3f74ef 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1309,7 +1309,8 @@ static int avi_read_idx1(AVFormatContext *s, int size)
         ast = st->priv_data;
 
         if (first_packet && first_packet_pos) {
-            data_offset = first_packet_pos - pos;
+            if (avi->movi_list + 4 != pos || pos + 500 > first_packet_pos)
+                data_offset  = first_packet_pos - pos;
             first_packet = 0;
         }
         pos += data_offset;