[FFmpeg-cvslog] ffmdec: limit the backward seek to the last resync position

[Andreas Cadhalpun]

ffmpeg | branch: master | Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com> | Mon Mar  9 14:59:44 2015 +0100| [6b8263b03ab3d16d70525ae1893cb106be7852f1] | committer: Michael Niedermayer

ffmdec: limit the backward seek to the last resync position

If resyncing leads to the same position as previously, it will again
lead to a resync attempt, resulting in an infinite loop.

Thus don't seek back beyond the last syncpoint.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni at gmx.at>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=6b8263b03ab3d16d70525ae1893cb106be7852f1
---

 libavformat/ffmdec.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/libavformat/ffmdec.c b/libavformat/ffmdec.c
index ee34e73..33bbde0 100644
--- a/libavformat/ffmdec.c
+++ b/libavformat/ffmdec.c
@@ -82,6 +82,7 @@ static int ffm_read_data(AVFormatContext *s,
     FFMContext *ffm = s->priv_data;
     AVIOContext *pb = s->pb;
     int len, fill_size, size1, frame_offset, id;
+    int64_t last_pos = -1;
 
     size1 = size;
     while (size > 0) {
@@ -101,9 +102,11 @@ static int ffm_read_data(AVFormatContext *s,
                 avio_seek(pb, tell, SEEK_SET);
             }
             id = avio_rb16(pb); /* PACKET_ID */
-            if (id != PACKET_ID)
+            if (id != PACKET_ID) {
                 if (ffm_resync(s, id) < 0)
                     return -1;
+                last_pos = avio_tell(pb);
+            }
             fill_size = avio_rb16(pb);
             ffm->dts = avio_rb64(pb);
             frame_offset = avio_rb16(pb);
@@ -117,7 +120,9 @@ static int ffm_read_data(AVFormatContext *s,
                 if (!frame_offset) {
                     /* This packet has no frame headers in it */
                     if (avio_tell(pb) >= ffm->packet_size * 3LL) {
-                        avio_seek(pb, -ffm->packet_size * 2LL, SEEK_CUR);
+                        int64_t seekback = FFMIN(ffm->packet_size * 2LL, avio_tell(pb) - last_pos);
+                        seekback = FFMAX(seekback, 0);
+                        avio_seek(pb, -seekback, SEEK_CUR);
                         goto retry_read;
                     }
                     /* This is bad, we cannot find a valid frame header */