[FFmpeg-cvslog] avformat/matroskadec: Improve check for level 1 duplicates

Andreas Rheinhardt git at videolan.org
Tue Jul 16 22:50:14 EEST 2019

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at gmail.com> | Fri May 17 00:30:21 2019 +0200| [806ac7da6927c1a9db2d6bc7af272733078964a0] | committer: James Almer

avformat/matroskadec: Improve check for level 1 duplicates

If a file uses unknown-length level 1 elements besides clusters and such
elements are after the first cluster, then these elements will usually
be parsed twice: Once during parsing of the file header and once when
reading the file reaches the position where these elements are located.
The second time the element is parsed leads to a "Duplicate element"
error message. Known-length elements are not affected by this as they
are skipped except during parsing the header.

This commit fixes this by explicitly adding a check for whether the
position of the element to be parsed is the same as the position of the
already known level 1 element.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=806ac7da6927c1a9db2d6bc7af272733078964a0

 libavformat/matroskadec.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 3abdf01374..b97189e674 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -1390,7 +1390,10 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
             matroska->cues_parsing_deferred = 0;
         if (syntax->type == EBML_LEVEL1 &&
             (level1_elem = matroska_find_level1_elem(matroska, syntax->id))) {
-            if (level1_elem->parsed)
+            if (!level1_elem->pos) {
+                // Zero is not a valid position for a level 1 element.
+                level1_elem->pos = pos;
+            } else if (level1_elem->pos != pos)
                 av_log(matroska->ctx, AV_LOG_ERROR, "Duplicate element\n");
             level1_elem->parsed = 1;

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