[vlc-devel] Matroska dummy

[Steve Lhomme]

I just realised that the EbmlParser class is also used to parse other
things than the Segment and its children (seek head for example). So this
code is incorrect.

I'll send a better patch.

On Wed, Feb 18, 2015 at 3:44 PM, Steve Lhomme <robux4 at gmail.com> wrote:

> Mh, my emails don't seem to go through with the videolabs alias... So here
> is the patch I made to fix the original issue, by not allowing anything but
> level-1 elements when we look for them. They are specially designed to
> avoid false alarm like in this case.
>
>
> ---
>  modules/demux/mkv/Ebml_parser.cpp | 25 ++++++++++++++++++++++++-
>  modules/demux/mkv/Ebml_parser.hpp |  1 +
>  2 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/modules/demux/mkv/Ebml_parser.cpp
> b/modules/demux/mkv/Ebml_parser.cpp
> index 21e219e..6041eaf 100644
> --- a/modules/demux/mkv/Ebml_parser.cpp
> +++ b/modules/demux/mkv/Ebml_parser.cpp
> @@ -146,6 +146,28 @@ void EbmlParser::Reset( demux_t *p_demux )
>      mb_dummy = var_InheritBool( p_demux, "mkv-use-dummy" );
>  }
>
> +
> +// Define a special Segment context that doesn't allow void/crc32 elements
> +static const EbmlSemanticContext & GetEbmlNoGlobal_Context();
> +static const EbmlSemanticContext Context_EbmlNoGlobal =
> EbmlSemanticContext(0, NULL, NULL, *GetEbmlNoGlobal_Context, NULL);
> +static const EbmlSemantic EbmlNoGlobal_ContextList[0] =
> +{
> +  //EbmlSemantic(false, false, EBML_INFO(EbmlCrc32)),   ///< EbmlCrc32
> +  //EbmlSemantic(false, false, EBML_INFO(EbmlVoid)),    ///< EbmlVoid
> +};
> +static const EbmlSemanticContext EbmlNoGlobal_Context =
> EbmlSemanticContext(countof(EbmlNoGlobal_ContextList),
> EbmlNoGlobal_ContextList, NULL, *GetEbmlNoGlobal_Context, NULL);
> +static const EbmlSemanticContext & GetEbmlNoGlobal_Context()
> +{
> +  return EbmlNoGlobal_Context;
> +}
> +
> +// the Segment Context should not allow Void or CRC32 elements to avoid
> lookup false alarm
> +const EbmlSemanticContext Context_KaxSegmentVLC =
> EbmlSemanticContext(KaxSegment_Context.GetSize(),
> +
> KaxSegment_Context.MyTable,
> +
> KaxSegment_Context.Parent(),
> +
> GetEbmlNoGlobal_Context,
> +
> KaxSegment_Context.GetMaster());
> +
>  EbmlElement *EbmlParser::Get( int n_call )
>  {
>      int i_ulev = 0;
> @@ -171,7 +193,8 @@ EbmlElement *EbmlParser::Get( int n_call )
>      }
>
>      /* Ignore unknown level 0 or 1 elements */
> -    m_el[mi_level] = m_es->FindNextElement( EBML_CONTEXT(m_el[mi_level -
> 1]),
> +    EbmlSemanticContext e_context = mi_level == 1 ? Context_KaxSegmentVLC
> : EBML_CONTEXT(m_el[mi_level - 1]);
> +    m_el[mi_level] = m_es->FindNextElement( e_context,
>                                              i_ulev, UINT64_MAX,
>                                              (  mb_dummy | (mi_level > 1)
> ), 1 );
>      if( i_ulev > 0 )
> diff --git a/modules/demux/mkv/Ebml_parser.hpp
> b/modules/demux/mkv/Ebml_parser.hpp
> index 57fdf23..96f9f4b 100644
> --- a/modules/demux/mkv/Ebml_parser.hpp
> +++ b/modules/demux/mkv/Ebml_parser.hpp
> @@ -60,6 +60,7 @@ class EbmlParser
>
>      int          mi_user_level;
>      bool         mb_keep;
> +    /* Allow dummy/unknown EBML elements */
>      bool         mb_dummy;
>  };
>
> --
> 1.9.5.msysgit.0
>
>
>
> On Wed, Feb 18, 2015 at 11:16 AM, Denis Charmet <typx at dinauz.org> wrote:
>
>> Hi,
>>
>> Le mercredi 18 février 2015 à 09:19:53, Steve Lhomme a écrit :
>> > I'm looking at this issue https://trac.videolan.org/vlc/ticket/9623
>> >
>> > This is a live stream from GStreamer that doesn't play in normal
>> condition.
>> > For playback to work you need to enable "--mkv-use-dummy" which allows
>> > unknown elements in Matroska.
>> >
>> > The problem is that a normal Matroska implementation *should* handle
>> > unknown elements by default and skip them. Some vendors or users might
>> add
>> > their own stuff (like DivX does) and VLC wouldn't play the files.
>> > libmatroska is not supposed to keep track of all known custom IDs
>> floating
>> > around and VLC be compiled with the latest for playback to work.
>>
>> By default it does. In fact I always check for dummy elements to detect
>> broken
>> files and silently discard them.
>>
>> Regards,
>>
>> --
>> Denis Charmet - TypX
>> Le mauvais esprit est un art de vivre
>> _______________________________________________
>> vlc-devel mailing list
>> To unsubscribe or modify your subscription options:
>> https://mailman.videolan.org/listinfo/vlc-devel
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.videolan.org/pipermail/vlc-devel/attachments/20150218/ee6ebdef/attachment.html>