https://debugmo.de/2007/07/read-your-dvds-the-raw-way/
This will be an attempt to document stuff I've done in the past. I'm bad at documenting, so I'll just present what I've done. If you have further questions, always feel free to email me.
This time I wanted to know what's on my DVDs. I mean, not what's normally visible, but what's underneath the data layer. Contrary to CDs, where a lot of work has been done to allow reading every bit of a CD, there is surprisingly less information for DVDs.
[...] CD readers often have special modes to read raw sectors. This is probably related to the fact that you need some of these functions to digitally read out audio data from audio CDs, but they can also be used to explore CD-ROMs. In the DVD-domain, we are not that lucky. Most of the signal processing is done in hardware, and recent drives are single-chip chipsets, with one chip doing all the work, from analog RF to IDE (or SCSI). Sometimes firmware allows you reading 2064 bytes per sector, sometimes you can disable the EDC check or scrambling, but usually, you cannot go further. Sometimes you can query PI/PO stats, but that's all.
[...] If you want to build your own debug DVD reader - well, start with finding the proper DVD-ROM. I'm sure there are a lot of (older) DVD-ROMs which have the right data ports. Take a scope, and watch for digital data. An easy way to tell if this data comes directly from DVD is to slow down the disc a bit (with your finger :) - only a bit, the drive needs to keep in sync! -, and watch if the data rate changes. If it does, chances are big that you found the right data. It should be approx. twice the payload data rate.
(Score: 1, Insightful) by Anonymous Coward on Tuesday October 15 2019, @10:16AM (1 child)
I feel sad. The author says "older DVD-ROM" in 2007. Seems a bit unlikely to find one now...
(Score: 3, Insightful) by Hyperturtle on Tuesday October 15 2019, @01:27PM
Yeah I noticed that before even properly reading the summary. Still... weirdos like me still do stuff like that on occasion; at least someone found it interesting enough to post.
The good news, is, however, that some information managed to stay online and useful until its utility had passed. That I can appreciate. As forever as the internet is, it usually isn't for very long beyond the lifecycle if there is a business interest behind it.
I wish the same could be said about OS patches from, as a totally random example, Microsoft, for various 'unsupported" operating systems of theirs.
(Score: 5, Insightful) by hwertz on Tuesday October 15 2019, @04:58PM (1 child)
Of course, the lack of raw read command on DVD drives is not some oversite. Remember, when DVDs came out, they had the fantasy that the rights restriction system on the DVDs would prevent anyone with a computer from reading the thing without a fully rights restricted, hollywood-approved and fully paid up piece of DVD player software.
(Score: 2) by Chocolate on Tuesday October 15 2019, @10:05PM
This was from before they learned that if DVD owners can't backup their disks they will stop buying them.
Bit-choco-coin anyone?