Twin Format layer to play selection issue for PC software player

Henry Gabryjelski henrygab at
Mon Aug 1 20:00:15 PDT 2005

* From the T10 Reflector (t10 at, posted by:
* "Henry Gabryjelski" <henrygab at>

Thank you for some information on what you think of the proposal.
Please allow a response and questions to each item you mention:

1. This is only correct for the current proposal, but not for the
Microsoft proposal.

2. You presume the user knows a disc has multiple layers.  However, this
is definitely not the case.  Users have only a round shiny disc, and it
is not clear without software or other UI what is on the disc.  We do
agree that minimally one physical layer may be able to be read by the
device the user has.

3. Thank you for providing some technical problems with random access
between layers.  This is very useful information for the discussion.
Please allow me to address this directly later.
4. You are saying that your preference is some user action.  I agree
that eject/load is not a best choice for a Twin Format disc.  Suggesting
that a list of physical formats can be shown before use of the disc is
possible does not allow for complex LU-host interaction as is common on
PCs.  I can say that such a model is currently extremely problematic for
Windows, and there are no simple solutions (all are very complex).  (I
cannot speak for other OS.)  I can understand that this model is simple
for consumer electronics devices, but why would CE devices display this

5. User interface issues are separate from MMC command set issue.
However, command sets designed without appropriate consideration of OS
design will result in a poor user experience.  You are correct that only
new drives will be affected.  However, new drives are often installed on
legacy OS.  My proposal is attempting to find a solution that does not
require changes to the OS to enable simple use of the TwinFormat disc.

6. Forgive me for not understanding.  I suggest no change to DVD file
system -- such a layer should always be session one.  Only change
required is to support notion of "multisession" for HD-DVD layer
(finding file system at non-zero LBA).  So, I think no changes are
required to the DVD file system specification nor to the DVD application

7. There is no disagreement.  If the proposed second session (HD-DVD
layer) does not reference the file system structures in the first
session, then the UDF file system in the second session will only
contain one type of UDF.  There is no violation of OSTA UDF, even if
session 1 is UDF 1.02 and session 2 is UDF 2.6.

Going back to item #3: You say that layer change for such a disc may be
comparable in time to spindle start/stop.  Currently, generic software
must already deal with auto-spin down.  Playback software will never
have random access to two layers.  So, I think the issue is not so
great, as there are no error cases not already dealt with by host OS
and/or software.  This means that the command spec need not make this a
major change.

Please help me to understand why you believe that SACD-CD twin format is
important?  I do not wish to limit to only HD-DVD/DVD Twin format disc.
Multi-session would also be OK for SACD-CD twin format, I think.
Multi-session would also work for BD-DVD and BD-CD twin format discs.
Twin Format disc should definitely be more smart than the both sided

Our discussion is to find a method to make this possible while requiring
only small changes from all parties (host, lu, playback software).  I do
not find it desirable to require any playback software to also write a
file system or other low-level software to work in Windows.  Therefore,
I work very hard to find solutions which enable playback software with
minimal changes to the OS, and to prevent items which cause user
confusion.  Making changes that require UI, which then effectively
changes the media, is not a model which enables these goals to be met.
I sincerely hope that, by discussing this on the list, we can reach a
compromise solution which works well for drive manufacturers, CE device
manufacturers, host OS companies, file system companies, and video
playback companies.

So, I understand that layer switch may be cause for spinup/spindown
delay.  Is this the only technical problem with my proposed solution?


-----Original Message-----
From: owner-mtfuji5 at
[mailto:owner-mtfuji5 at] On Behalf Of
keiji_katata at
Sent: Monday, August 01, 2005 7:27 PM
To: mtfuji5 at
Cc: t10 at
Subject: RE: Twin Format layer to play selection issue for PC software

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
label side, this is difficult for the both sided disc.

Random access between different physical format layers is not
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.
color change, RF signal circuit/signal decoder change, servo system
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.
it may decrease the advantage of the Twin Format disc. A list of
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
In case of some specific device, one physical format layer will be
to mount automatically. For example, DVD player (e.g. DVD only device,
playback software) can mount DVD layer only, then may mount the DVD
physical layer. Therefore physical format layer change is possible only
the system that supports Twin Format layer disc. Therefore supported
application, OS and device are necessary. The system vender will design
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
can not be mapped on UDF. I think we should not limit our discussion
for DVD-HD DVD Twin Format disc.

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

Best regards,

Keiji Katata

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