Signedness bug in Matroska PTS calculation

With some mkv files I had many discontinuity events. I found out that if
changing the timecode_diff in demux_matroska.c from int to int16_t fixes
this problem. Using int will never produce negative values if int is not
16-bit...

2 files changed, 3 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 3ed085f08..c988d78f5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,6 @@
 xine-lib (1.1.17) 2009-??-??
   * Build fixes related to ImageMagick 6.4 & later.
+  * Fix an error in Matroska PTS calculation.
   * Enable libmpeg2new. This is not yet production code; the old mpeg2
     decoder remains the default.
   * Fix a broken size check in the pvr input plugin (ref. CVE-2008-5239).
diff --git a/src/demuxers/demux_matroska.c b/src/demuxers/demux_matroska.c
index 086e0cc98..37f4bd95b 100644
--- a/src/demuxers/demux_matroska.c
+++ b/src/demuxers/demux_matroska.c
@@ -1867,7 +1867,7 @@ static int parse_block (demux_matroska_t *this, size_t block_size,
   uint8_t          *data;
   uint8_t           flags;
   int               gap, lacing, num_len;
-  int               timecode_diff;
+  int16_t           timecode_diff;
   int64_t           pts, xduration;
   int               decoder_flags = 0;
 
@@ -1877,7 +1877,7 @@ static int parse_block (demux_matroska_t *this, size_t block_size,
   data += num_len;
 
   /* timecode_diff is signed */
-  timecode_diff = parse_int16(data);
+  timecode_diff = (int16_t)parse_int16(data);
   data += 2;
 
   flags = *data;