[Matroska-devel] [Cellar] Depth offsets for subtitles in case of 3D MVC tracks in MKV files

Nithin Mathew Kurien via Matroska-devel matroska-devel at lists.matroska.org
Tue Jan 26 14:39:21 CET 2016


It's like this. Suppose the MVC video track has 8 frames. Also suppose it
has 5 Offset Metadata Sequences embedded in it at the time of encoding.
(Sequence entries are in pixels, positive if in front of the screen, and
negative if behind.)

*Frame*  *1  2  3  4  5  6  7  8*
*Seq1*    5  1 -8 -2 -9  1 -3 -1
*Seq2*    8  1  0  8 -4 -5  4 -1
*Seq3*   -2  8 -3 -5  7  5 -5 -4
*Seq4*    9  0  0 -5 -2  1 -4 -1
*Seq5*   -9  3 -2 -4 -6  0 -3  6

If the M2TS container has 2 subtitle tracks P1, P2 and 1 menu track I1,
then a mapping can be defined in the M2TS container like this:
P1 : Seq1
P2 : Seq3
I1  : Seq4

So basically, *the sequences are defined in the MVC track and the mapping
is defined in the M2TS container.* If this mapping is not defined in the
container, the player would display the subtitle or menu track at the plane
of the screen. Thus the outcome would be as if a sequence whose all entries
are 0, is assigned to the subtitle or menu track. This has been a problem
with the few hardware media players supporting MVC inside MKV, for example
the Mede8er ones (http://www.mede8erforum.com/index.php?topic=9624.0).

Ideally, a menu track should be displayed in front of the subtitle track,
which should be in front of the video track. This can be done through the
proper definitions of sequences and mappings. The free program
MVCPlanes2OFS.exe from the package BD3D2MK3D (
http://forum.doom9.org/showthread.php?t=170828) can display all Offset
Metadata Sequences embedded in a .MVC file.

Thanks and regards,

On Tue, Jan 26, 2016 at 6:46 PM, madshi <madshi at gmail.com> wrote:

> 2016-01-26 13:34 GMT+01:00 Steve Lhomme via Matroska-devel
> <matroska-devel at lists.matroska.org>:
> > I'm not sure I understand. Is the offset per track or per frame for
> > the subtitle ? If it's per track it should go in the Track Info. If
> > not that means a mechanism to add that information for each frame.
> > Maybe BlockGroup could help.
> The 3D Blu-Ray spec says:
> > P. Offset metadata
> > The offset_metadata() shall be stored in the user data container
> > (defined in which is contained in MVC scalable nesting
> > SEI message of the first view component of each GOP of MPEG-4
> > MVC Dependent view video stream in decoding order.
> I'm not a big expert on these things, but doesn't that mean it's part
> of the MVC video bitstream? In that case there's probably no need to
> store it in separate MKV fields/properties?
> Best regards, Mathias.
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