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- Newsgroups: alt.cd-rom
- Path: sparky!uunet!mcsun!sun4nl!relay.philips.nl!philica!adrie
- From: adrie@ica.philips.nl (Adrie Koolen)
- Subject: Re: CDROM-XA and Photo-CD
- Message-ID: <1992Nov11.162135.999@ica.philips.nl>
- Organization: Philips Consumer Electronics, Eindhoven, The Netherlands
- References: <1dc6bnINNs82@darkstar.UCSC.EDU> <1992Nov9.090424.280@ica.philips.nl> <A.Grant.21.721318849@ucs.cam.ac.uk>
- Date: Wed, 11 Nov 1992 16:21:35 GMT
- Lines: 46
-
- In article <A.Grant.21.721318849@ucs.cam.ac.uk> A.Grant@ucs.cam.ac.uk (Alasdair Grant) writes:
- >Thanks, that is very clear. A few questions:
- > - Photo-CD and Sony Electronic Books use an ISO 9660 file structure on
- > mode-2/form-1 sectors, right?
-
- Indeed, the PhotoCD uses an ISO 9660 file structure on mode-2/form-1
- sectors. On a CDROM/XA, one may also use files with mode-2/form-2 sectors
- but Kodak decided not to use them. I think that they don't use mode-2/
- form-2 sectors because it makes hard/software somewhat more complex.
-
- I don't know the Sony Electronics Book.
-
- > - mode-2/form-2 is _exactly_ the format used by audio CDs, right?
-
- No, no! Audio tracks contain blocks with no substructuring whatsoever.
- Thus no sync field, no header, no subheader and no EDC/ECC bytes. Just
- 2352 bytes (1176 words) of audio samples (588 16 bits stereo samples).
-
- > - doesn't CD-ROM/XA specify particular encoding formats for image and
- > audio?
-
- Yes, at least the audio part (ADPCM sound groups) are defined. On video,
- clut7, rll4, rll7, yuv, etc, are defined, but not the PhotoCD format.
-
- > - since the purpose of the two forms of mode-2 sectors was to allow more
- > flexibility in storing complex multimedia data than was possible when
- > data/audio selection was on a track-by-track basis, wouldn't CDROM-XA
- > compatibility require being able to read _both_ forms of sector?
-
- Of course. But to read PhotoCD, you could live with mode-2/form-1 sectors
- only. When PhotoCD adds ADPCM audio, you really need to be able to read
- mode-2/form-1 sectors also (and, of course, you need an audio system that
- can decode and play ADPCM sectors).
-
- > Clearly, the design of some (but not all) file systems makes it hard to
- > have 2324-byte blocks...
- > - is there any reason now for the existence of mode 1 tracks other than
- > for people with old non-XA drives?
-
- Not really. Mode-2/form-1 sectors use the same ECC algorithm as with mode-1
- sectors, so reliability should be the same. (Note that I neglect the fact
- that the data over which the EDC/ECC rules are smaller than with mode-1
- sectors.)
-
- Adrie Koolen (adrie@ica.philips.nl)
- Philips Consumer Electronics, Eindhoven, the Netherlands
-