By Jan Willem @ http://www.cdfreaks.com/article/150
Compatibility is an important issue when it comes to DVD recording. Because there are three rivalling formats (DVD+RW, DVD-RW and DVD-RAM) not every DVD player is compatible with each disc. Even discs within each format do not always work on every player. In this article we will explain how to make some discs more compatible, why you need it and how it works.
In the past not every CD worked with every player and even nowadays people report that some bad discs do not work with every player (E.g. car audio players are known to be more picky). The DVD format didn't change the compatibility, it even made it worse. At the moment there are three different DVD recordable formats and all of them are different and require the DVD player to do different things. However the compatibility is still improved and the chance of a non working DVD recordable / DVD player combination is relatively small (think about 10-20%).
We will focus on DVD-R and DVD+RW as DVD-RAM is hardly used and uses a technique that is totally different from DVD-R and DVD+R. The DVD-R format is the oldest DVD recordable format and its original compatibility was good and is probably the best out of the box. Although the DVD-R format is marketed as the oldest and most compatible DVD recordable format, this isn't necessarily the case.
Difference between DVD-R and DVD+R
Physically there is a difference between a DVD-R disc and a DVD+R disc that is made during the production process. During the production of a DVD-R disc the lead-in is pre-embossed (pre-written). This overwrites parts of the DVD that contains information about the disc. E.g. the CSS key (part of the copy protection) is in this part on commercial movie discs (This is why you can?t make a 1:1 copy of a DVD). But in this space there is also room reserved for the so called ?booktype? field.
Changing the booktype field
This booktype field identifies the disc as either a DVD-ROM, DVD+R(W) or a DVD-R(W) disc and is for a big part responsible for the compatibility. Because this setting is overwritten during the DVD-R production process it can?t be modified afterwards, the laser of your DVD recorder simply can?t write to that part of the disc. During the production of DVD+R discs the space is untouched. Still CSS keys can?t be written to DVD+R discs because every DVD recorder and DVD player has a limit in its firmware to write or read to this space. However, there is no limit for writing the booktype field. Therefor a DVD+R(W) recorder will be able to modify this field by sending a command to the DVD recorder and fool the DVD player.
When the booktype field (bitsetting) is changed to DVD-ROM then DVD players are fooled and will think the user has put in a DVD-ROM disc instead of a DVD+R disc and will read it accordingly. This results in an increased chance that the player is able to read the disc and that?s why the ability to change the booktype field (bitsetting) is essential to a lot of users. Certainly owners of a DVD player that requires this field to be set to DVD-ROM, in order to work properly, will prefer a DVD recorder that supports setting the booktype field.
Although you will understand that it?s not possible to change the booktype field for DVD-R discs there still excists a DVD-R bitsetting. Some claim that this increases the compatibility but this has not been independently confirmed by anyone and as it?s technically impossible to change the booktype field it will still be possible for the hardware to find out that a disc is a DVD-R. The booktype setting for DVD-R discs seems to be based on a workaround that has not been proven to be working.
According to Michael Spath who studies both the +R and -R format and is known as an expert on technical DVD recording issues; "the trick is based on the fact that some drives read the booktype from the last border-in and not from the lead-in. Therefore if you create a second session on the disc you will create after the first session a new border-in, where you should normally copy the informations from the lead-in (including the book type). With this trick, you instead write a DVD-ROM booktype in this second session, which violates the - standard. Also drives which read the booktype from the lead-in will not be fooled by this method (eg. some Pioneer drives". An intresting discussion about this can be found here.
The booktype field can be modified by several applications. Best known is Nero which allows you to modify field the booktype field for several brands of DVD recorders. Companies such as Lite-On, BTC, NU-Tech, Ricoh and BenQ have released tools to modify the booktype field. Firmware hacks (E.g. NEC) also are able to set the default booktype to DVD-ROM. Other companies such as LG have announced it will add support and Philips automatically changes the booktype using the firmware of the drive. Plextor has till now said it will not support it because it's not according to the DVD+R specifications. On our forum you will find many discussions on the several applications.
More technical information about the difference between DVD-R and DVD+R can be found here. Check here if there are reports that your favorite brand DVD recordables does not work with your DVD player.