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To read a UDF disk logically, several critical sectors must be read, that then set pointers to the next critical sector.  The first such sector is the Anchor  Volume Descriptor.  The documentation states that there should be at least 2 such anchor blocks in three possible locations

• At sector 256 (100h)
• At the final sector of the disk
• 256 blocks before the final sector of the disk

It is quite possible to have a recoverable CD or DVD with no valid Anchor block, and so manual intervention is required.  As the Anchor block only contains information on where the Main Volume Descriptor is stored, all that needs to be entered is the location, and length of the main volume descriptor.  Alternatively, the Search function can be used, this may be slow (hence the cancel function).

Main Volume Descriptor

The main volume descriptor is a sector that stats with the hex bytes  01 00 and the bytes in offset 12-15 is the sector number in little endian format

Typical pointers to look are the name in offset 0x1a, and OSTA strings.

If the search function does not find the relevant sector, it may be worth while looking through sectors by hand. Typically it will be in a location in the low 200H, or may be 40H

If it is not possible to find a main volume descriptor, then it is likely that other critical sectors will also be missing.