[vlc-devel] Matroska dummy

Steve Lhomme robux4 at gmail.com
Wed Feb 18 10:43:01 CET 2015

On Wed, Feb 18, 2015 at 10:13 AM, Jean-Baptiste Kempf <jb at videolan.org>

> On 18 Feb, Steve Lhomme wrote :
> > 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.
> This option makes no sense. Just remove it.

The "strict" mode was made for files with damaged data, so that we can
recover to normal playback if odd values are found. Skipping data byte by
byte until we find something suitable again.

The "dummy" (skip unknown elements) mode treats these odd/damaged data as
proper EBML values and skip them. Until luckily, it finds data it can
handle again. In this case if the file has damaged data, these damaged data
will make it skip in the wrong places, finding more incorrect data to parse
and ending up not reading anything correctly. That can happen with a mkv
not completely loaded from torrent. I think that's why it's not the default

Both have their use and are currently mutually exclusive. I think it's
unrealistic to ask people to enter some command-line param to play some
files. Especially if they're trying to play from Android or iOS. So we must
find another solution.

It should be possible to use "dummy" elements in the header and until the
first Cluster is found. And then switch to strict mode so that if we
encounter damaged data we just skip the bad parts until we find something
playable again.

> > IMO this option is backward. The doc says "Read and discard unknown EBML
> > elements (not good for broken files)." It should be the other way around.
> > If you have a file that doesn't play, then you can try a command-line
> > option for playback to work.
> Just invert the default, it's quite easy.
> -
> With my kindest regards,
> --
> Jean-Baptiste Kempf
> http://www.jbkempf.com/ - +33 672 704 734
> Sent from my Electronic Device
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