[vlc-commits] demux/mkv: abort EnsureDuration on non-finite elements

[Filip Roséen]

vlc | branch: master | Filip Roséen <filip at atch.se> | Fri Nov  4 16:47:08 2016 +0100| [46e632dd060e6f3f70679af83f3d9efb7a1be733] | committer: Thomas Guillem

demux/mkv: abort EnsureDuration on non-finite elements

matroska_segment_c::EnsureDuration is used to calculate the duration
for a stream which does not include the value as metadata. Given that
the function potentially will have to run through the entire file in
order to get the last timecode, these changes make sure that we abort
if an element does not have a finite size.

If an element, on the way, does not have a finite size we cannot
simply jump over it, but have to parse it's entire contents (which
might be an expensive operation). And most often when an element does
not have a finite size, the media is being streamed.

We however have an exception to infinite clusters that are referenced
by a Cue, in which case we will try to parse it (to allow content
saved from a live stream where the Cues refers to every cluster to
have a duration).

Signed-off-by: Steve Lhomme <robux4 at videolabs.io>
Signed-off-by: Thomas Guillem <thomas at gllm.fr>

> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=46e632dd060e6f3f70679af83f3d9efb7a1be733
---

 modules/demux/mkv/matroska_segment.cpp | 62 +++++++++++++++-------------------
 1 file changed, 27 insertions(+), 35 deletions(-)

diff --git a/modules/demux/mkv/matroska_segment.cpp b/modules/demux/mkv/matroska_segment.cpp
index b2323d7..016748b 100644
--- a/modules/demux/mkv/matroska_segment.cpp
+++ b/modules/demux/mkv/matroska_segment.cpp
@@ -687,7 +687,7 @@ bool matroska_segment_c::Preload( )
 
     b_preloaded = true;
 
-    if( cluster && cluster->IsFiniteSize() )
+    if( cluster )
         EnsureDuration();
 
     return true;
@@ -981,61 +981,53 @@ void matroska_segment_c::EnsureDuration()
 
     bool b_seekable;
 
-    vlc_stream_Control( sys.demuxer.s, STREAM_CAN_FASTSEEK, &b_seekable );
-    if ( !b_seekable )
+    if( vlc_stream_Control( sys.demuxer.s, STREAM_CAN_FASTSEEK, &b_seekable ) ||
+        !b_seekable )
     {
         msg_Warn( &sys.demuxer, "could not look for the segment duration" );
         return;
     }
 
     uint64 i_current_position = es.I_O().getFilePointer();
-    uint64 i_last_cluster_pos = 0;
+    uint64 i_last_cluster_pos = cluster->GetElementPosition();
 
     // find the last Cluster from the Cues
+
     if ( b_cues && _seeker._cluster_positions.size() )
-    {
         i_last_cluster_pos = *_seeker._cluster_positions.rbegin();
-    }
+    else if( !cluster->IsFiniteSize() )
+        return;
 
-    // find the last Cluster manually
-    if ( !i_last_cluster_pos && cluster != NULL )
-    {
-        es.I_O().setFilePointer( cluster->GetElementPosition(), seek_beginning );
+    es.I_O().setFilePointer( i_last_cluster_pos, seek_beginning );
+
+    EbmlParser eparser ( &es, segment, &sys.demuxer, var_InheritBool(
+          &sys.demuxer, "mkv-use-dummy" ) );
 
-        EbmlElement* el;
-        EbmlParser ep( &es, segment, &sys.demuxer,
-                             var_InheritBool( &sys.demuxer, "mkv-use-dummy" ) );
+    // locate the definitely last cluster in the stream
 
-        while( ( el = ep.Get() ) != NULL )
+    while( EbmlElement* el = eparser.Get() )
+    {
+        if( !el->IsFiniteSize() && el->GetElementPosition() != i_last_cluster_pos )
         {
-            if ( MKV_IS_ID( el, KaxCluster ) )
-            {
-                i_last_cluster_pos = el->GetElementPosition();
-            }
+            es.I_O().setFilePointer( i_current_position, seek_beginning );
+            return;
         }
+
+        if( MKV_IS_ID( el, KaxCluster ) )
+            i_last_cluster_pos = el->GetElementPosition();
     }
 
     // find the last timecode in the Cluster
-    if ( i_last_cluster_pos )
-    {
-        es.I_O().setFilePointer( i_last_cluster_pos, seek_beginning );
-
-        EbmlParser eparser (
-            &es , segment, &sys.demuxer, var_InheritBool( &sys.demuxer, "mkv-use-dummy" ) );
 
-        KaxCluster *p_last_cluster = static_cast<KaxCluster*>( eparser.Get() );
-        if( p_last_cluster == NULL )
-            return;
+    eparser.Reset( &sys.demuxer );
+    es.I_O().setFilePointer( i_last_cluster_pos, seek_beginning );
 
-        if( !ParseCluster( p_last_cluster, false, SCOPE_PARTIAL_DATA ) )
-            return;
-
-        if( p_last_cluster->IsFiniteSize() == false )
-        {
-            es.I_O().setFilePointer( i_current_position, seek_beginning );
-            return;
-        }
+    EbmlElement* el = eparser.Get();
+    MKV_CHECKED_PTR_DECL( p_last_cluster, KaxCluster, el );
 
+    if( p_last_cluster &&
+        ParseCluster( p_last_cluster, false, SCOPE_PARTIAL_DATA ) )
+    {
         // use the last block + duration
         uint64 i_last_timecode = p_last_cluster->GlobalTimecode();
         for( unsigned int i = 0; i < p_last_cluster->ListSize(); i++ )