[FFmpeg-devel] [PATCH 03/21] avformat/matroskadec: Get rid of cluster size field assumption

[Andreas Rheinhardt]

The earlier code relied on the length of clusters always being coded on
eight bytes (as is current Matroska muxer behaviour). But there is no
need to rely on this and this commit changes it.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at googlemail.com>
---
 libavformat/matroskadec.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 7a96e53bdd..f3bc792728 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -3694,14 +3694,16 @@ static int webm_clusters_start_with_keyframe(AVFormatContext *s)
     before_pos = avio_tell(s->pb);
     while (1) {
         int64_t cluster_id = 0, cluster_length = 0;
+        int read;
         AVPacket *pkt;
         avio_seek(s->pb, cluster_pos, SEEK_SET);
         // read cluster id and length
-        ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
-        ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
-        if (cluster_id != 0xF43B675) { // done with all clusters
+        read = ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
+        if (read < 0 || cluster_id != 0xF43B675) // done with all clusters
+            break;
+        read = ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
+        if (read < 0)
             break;
-        }
         avio_seek(s->pb, cluster_pos, SEEK_SET);
         matroska->current_id = 0;
         matroska_clear_queue(matroska);
@@ -3710,7 +3712,8 @@ static int webm_clusters_start_with_keyframe(AVFormatContext *s)
             break;
         }
         pkt = &matroska->queue->pkt;
-        cluster_pos += cluster_length + 12; // 12 is the offset of the cluster id and length.
+        // 4 + read is the length of the cluster id and the cluster length field.
+        cluster_pos += 4 + read + cluster_length;
         if (!(pkt->flags & AV_PKT_FLAG_KEY)) {
             rv = 0;
             break;
-- 
2.19.2