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Comment by sbaiddn | Hacker News Reader

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?

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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.

So the error are used to trip traditional tools like ddrescue like in the days of old?

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.ap...

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.ap...

https://www.xiph.org/paranoia/

https://cdrdao.sourceforge.net/

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 ;)

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

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.

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