[DVDnav-discuss] Patch from the Living dead for dvdnav

[John Stebbins]

On 11/02/2011 04:58 PM, Jean-Baptiste Kempf wrote:
> On Wed, Nov 02, 2011 at 04:46:13PM -0700, John Stebbins wrote :
>> Am I reading this cross-eyed or is this just totally stupid?
> This is totally stupid.
>
> Looking closer, the patch evolved during the mess, the original,
> attached here, was less stupid, but seems to depend on a non-installed
> dvdread header.
>
>
After reading this over, I think I see what is going on here.  This patch is using the ECMA-167 primary volume
descriptor that is located at sector 16 instead of the UDF primary volume descriptor that the original code assumes is
at sector 32.  If I'm reading the UDF specification correctly, there is no guarantee that the UDF primary volume
descriptor will be at this location.  You need to read an anchor volume descriptor pointer first which will point to the
main volume descriptor.  So maybe there are some discs out the for which the original code does not work.

The patch however is doing something pretty funky for the serial number.  It is using the volume creation date as a
serial number which isn't going to be unique by any measure.  The original code uses the first 16 bytes of the volume
set identifier (which is 128 bytes in length).  Looking at a sample of the volume set identifier, the first 8 bytes look
like some kind of serial number. The next 8 are zero. And then the disc title is repeated again.

Anyway, it might be interesting to think about doing a patch that look up the udf volume descriptor correctly instead of
falling back to the ecma-167 volume descriptor.

-- 
John      GnuPG fingerprint: D0EC B3DB C372 D1F1 0B01  83F0 49F1 D7B2 60D4 D0F7


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