[plug] CUE/BIN vs ISO

[Craig Ringer]

> dd'ing /dev/cdrom will only copy /one/ data track; this is fine for most
> data CDs which only contain one track, but specialised software is
> needed to get an exact copy of a CD containing audio or >1 track.

That was also my understanding. It is for this reason that you can 
'mount /dev/hdc' not 'mount /dev/hdc1' where 'hdc1' is track 0 of the CD 
/dev/hdc. It'd be cool to have a multi-device interface to CDs, but 
aforementioned block size problems, lack of error correction on audio 
data, etc would get in the way.

> | Think about it, how else can things like playstation 1 games, 'special' 
> | audio cds and the likes all get copyed when the OS can't read the file 
> | system?
> 
> In the case of audio CDs, special magic ioctl()s :-)  No idea about
> video CDs or playstation games, but presumably they are either data CDs
> in disguise or equivalent to audio.

I'm pretty sure a VCD is an ISO9660 data track with a special file 
structure for metadata, followed by one or more tracks without 
error-correction data (like audio tracks) containing MPEG program 
streams. I've made the odd VCD, but it was a while ago now - I can't 
remember the details for sure.

I don't think dd'ing a VCD or DVD would work - you'd need to use a 
program that knows how to use the appropriate ioctl's to access the full 
disc.

> | p.s. If you disagree with anything said and can prove it then please do. I 
> | am going mainly on experience as part of my work involves making exact 
> | images of cds for storage.

And you definitely use `dd` not `readcd`, `cdrecord`, or `cdrdao`? 
Weird. It'd work for CDs with one data track only and no special 
requirements (ie specific TOC structure), but shouldn't handle audio 
CDs, VCDs, or much else.

> | p.p.s In regards to getting a cd sample, if it an audio cd chances are 
> | their will be errors when it gets read. A data cd will get re-read until it 
> | is read without errors, and audio cd it is usually a single bit every now 
> | and then and can't be heard but the output file will be different. When I 
> | get time i will write about this in more depth and post it.
> 
> Wrong again, I believe - at least if you're using software like
> cdparanoia or EAC. 

CDparanoia does multiple overlapping reads, tries to re-read bad audio 
data, etc, but that's all in software. With a data track the CD-ROM 
takes care of it, and uses ECC/CRC data that's not present in the audio 
tracks to help it. Other audio software may just accept whatever the 
CD-ROM feeds it.

Craig Ringer


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