Twin Format layer to play selection issue for PC software player

keiji_katata at keiji_katata at
Mon Aug 1 19:27:03 PDT 2005

* From the T10 Reflector (t10 at, posted by:
* keiji_katata at
Hello all,
When we discuss about Twin Format layer disc, I think we can assume
following things.

The usage of the Twin Format disc is very similar to the both sided disc
(one side is CD, the other side is DVD). But Twin Format disc should be
more smart than the both sided disc from the end user point of view.

User (disc owner) knows that the disc that user bought has multiple of
different physical layers on a side of the disc. Minimally one physical
layer may be able to be read by the device that the user has.
What content is recorded should be shown on the disc label. Because of no
label side, this is difficult for the both sided disc.

Random access between different physical format layers is not recommended.
To change the physical format layer from one to other, it may take very
long time comparing with the layer change of DVD-ROM dual layer disc. Laser
color change, RF signal circuit/signal decoder change, servo system change,
and disc rotation speed change are necessary. In some cases, it may be
similar to Spindle stop/restart.

To change the physical layer from one to the other, some user action has
been taken (is necessary). It should not be ejecting and loading. Because
it may decrease the advantage of the Twin Format disc. A list of Physical
Format layers may be shown. And then user may select a Physical Format
layer in the list.

User interface issue should be independent from the MMC command set issue.
In case of some specific device, one physical format layer will be selected
to mount automatically. For example, DVD player (e.g. DVD only device, DVD
playback software) can mount DVD layer only, then may mount the DVD
physical layer. Therefore physical format layer change is possible only on
the system that supports Twin Format layer disc. Therefore supported
application, OS and device are necessary. The system vender will design own
user interface.
Of course the MMC command set should be usable/useful for the system

Different Physical Format layer uses different file system specification
and different application specification. DVD is legacy specification.
Therefore it is not good idea that because of the MMC command set
implementation issue, we change DVD file system specification and DVD
application specification.

Optical disc uses OSTA UDF. OSTA UDF says that one volume space can have
only one type of UDF. MMC command set should not request to change the
basic UDF requirement.

In addition, already SACD-CD Twin Format disc exists. CD Audio track system
can not be mapped on UDF. I think we should not limit our discussion only
for DVD-HD DVD Twin Format disc.

I know the discussion in DVD Forum. I know the discussion in BDA. BDA also
is talking about BD-DVD, BD-CD Twin Format disc. In both party cases, the
usage is very similar to the both sided disc. I think that Twin Format disc
should be more smart than the both sided disc from the end user point of

Best regards,

Keiji Katata

* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at

More information about the T10 mailing list