@@ -77,6 +77,7 @@ 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) {

@@ -96,9 +97,11 @@ 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);

@@ -112,7 +115,9 @@ 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 */