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An Anonymous Coward writes:

https://debugmo.de/2007/07/read-your-dvds-the-raw-way/ [debugmo.de]

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.

While DVDs seem to be similar to CDs, there are many structural differences in the way the data is encoded. I’ll spare you the facts - in doubt, you want to read any of the (free) Ecma documents on DVDs (for example Ecma 268). They explain pretty much how DVD data is encoded on disc. But to sum it up: Before the data is written to DVD, it goes trough the following stages:

        addition of header data (ID,CPR.MAI,…)
        EDC calculation
        energery dispersal (scrambling)
        ECC (PI/PO)
        interleaving, adding sync information
        EFM+ encoding
        conversion to analog signal to drive burn laser for pits&lands

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.

Original Submission