3 ms·

Can someone explain to me why this is needed vs an imagining tool (say ddrescue)? Is there no tool that actually makes a bit perfect copy yet?

einherjae 4y ago
There’s a lengthy explanation in the wiki linked from the github page. But basically cd drives don’t give you a raw stream, and does stuff like error correction.
- sbaiddn 4y ago
  So the error are used to trip traditional tools like ddrescue like in the days of old?
  - einherjae 4y ago
    The drive itself abstracts out the raw stream if I understood things correctly. Similar to how a PC floppy controller can’t do a low level disk image, because it does some interpretation of the signal before handing it over to the system. One example mentioned was that drives generally don’t read the precise samples you ask for. https://web.archive.org/web/20160528213242/https://thomas.apestaart.org/thomas/trac/wiki/DAD/Rip https://web.archive.org/web/20160528213242/https://thomas.ap...
haunter 4y ago
ddrescue can't read audio tracks, Audio CDs doesn't have a file system in the traditional sense either etc. It's not meant for copy Audio CDs but CD-ROMs That's why CDRDAO or CDDA Paranoia exist for decades. https://web.archive.org/web/20160528213242/https://thomas.apestaart.org/thomas/trac/wiki/DAD/Rip https://web.archive.org/web/20160528213242/https://thomas.ap... https://www.xiph.org/paranoia/ https://www.xiph.org/paranoia/ https://cdrdao.sourceforge.net/ https://cdrdao.sourceforge.net/
- joshenders 4y ago
  Well, ddrescue can definitely “read audio tracks” and is perfectly suited for making archival copies of Audio CDs but it sounds like the problem you’re actually trying to solve is interpreting the data as Red Book CD-DA and decoding it into chunks you call files ;)
- sbaiddn 4y ago
  Why does ddrescue care about "file systems"? Again, I was under the impression that ddrescue does bit by bit copying that I can then mount (and tell it the "filesystem" required). Is this false? I have also noticed that, sometimes, ddrescue has trouble ripping dvds, chocking out or producing a low quality rip, that will play perfectly on the same hardware with VLC
  - ectopod 4y ago
    ddrescue works with blocks and bytes. Audio cds are different. They contain a single physical bit stream interpreted as several interleaved logical bit streams representing e.g. audio, position, metadata, error correction. They are not a sequence of bytes. Cdroms and dvds put a block and byte abstraction on top of this so ddrescue can do something with them.

einherjae 4y ago

There’s a lengthy explanation in the wiki linked from the github page. But basically cd drives don’t give you a raw stream, and does stuff like error correction.

sbaiddn 4y ago
So the error are used to trip traditional tools like ddrescue like in the days of old?
- einherjae 4y ago
  The drive itself abstracts out the raw stream if I understood things correctly. Similar to how a PC floppy controller can’t do a low level disk image, because it does some interpretation of the signal before handing it over to the system. One example mentioned was that drives generally don’t read the precise samples you ask for. https://web.archive.org/web/20160528213242/https://thomas.apestaart.org/thomas/trac/wiki/DAD/Rip https://web.archive.org/web/20160528213242/https://thomas.ap...

haunter 4y ago

ddrescue can't read audio tracks, Audio CDs doesn't have a file system in the traditional sense either etc. It's not meant for copy Audio CDs but CD-ROMs That's why CDRDAO or CDDA Paranoia exist for decades. https://web.archive.org/web/20160528213242/https://thomas.apestaart.org/thomas/trac/wiki/DAD/Rip https://web.archive.org/web/20160528213242/https://thomas.ap... https://www.xiph.org/paranoia/ https://www.xiph.org/paranoia/ https://cdrdao.sourceforge.net/ https://cdrdao.sourceforge.net/

joshenders 4y ago
Well, ddrescue can definitely “read audio tracks” and is perfectly suited for making archival copies of Audio CDs but it sounds like the problem you’re actually trying to solve is interpreting the data as Red Book CD-DA and decoding it into chunks you call files ;)
sbaiddn 4y ago
Why does ddrescue care about "file systems"? Again, I was under the impression that ddrescue does bit by bit copying that I can then mount (and tell it the "filesystem" required). Is this false? I have also noticed that, sometimes, ddrescue has trouble ripping dvds, chocking out or producing a low quality rip, that will play perfectly on the same hardware with VLC
- ectopod 4y ago
  ddrescue works with blocks and bytes. Audio cds are different. They contain a single physical bit stream interpreted as several interleaved logical bit streams representing e.g. audio, position, metadata, error correction. They are not a sequence of bytes. Cdroms and dvds put a block and byte abstraction on top of this so ddrescue can do something with them.