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CHD CD images do not retain CD-TEXT data
MAME version
0.269
System information
n/a
INI configuration details
n/a
Emulated system/software
n/a
Incorrect behaviour
Since CHD is a format for preservation, I would expect that all properties of CDs should be supported. Unfortunately, CD_TEXT data is not among it, getting completely lost in the creation of a CHD. Roundtripping from a CD image to CHD and back to CD will not produce an identical CD as what was input.
Expected behaviour
That CD-TEXT data gets preserved in CHDs.
Steps to reproduce
I'll provide an example CD file here (one second long, single track, with basic CD-TEXT info):
chdman createcd -i silent.toc -o silent.chdchdman extractcd -i silent.chd -o silent2.toc
After this step, you can examine that the silent2.toc file does not posses the CD-TEXT information found in the input file.
Additional details
CD-TEXT is a bit of a rare extension to the audio CD format. Out of hundreds of CDs I own, maybe only a dozen of them have CD-TEXT data. There was always a chicken-and-egg problem with adoptions ("players don't support it so I won't include it" and "CDs don't have it, my player doesn't need to have it"), but it does exist in some commercial releases.
Given it is a standard of the CD Audio format (works on mixed-mode CDs too!), I believe it makes sense for CHD to preserve the data and allow it to round-trip.
I'll give warning that my little demo file is far from an exhaustive example, but the cdrdao man page describes all the options available. :-)
Is this a specific case of the known issue of the CHD-CD format failing to include subchannel information?
There are two parts to CD TEXT – lead-in area info (MODE=4), and program area info (MODE=2). The CD TEXT data is stored in subcodes U to W (6 bits), organsied as packs of 24×6 bits and blocks of 8 packs (96×6 bits total). So technically, yes, it’s a case of not retaining subchannel information.
However, CHDs always contain a cooked table of contents rather than the raw lead-in content that the CD-ROM drive parses to obtain it. So to store the MODE=4 CD TEXT data, we’d need to either come up with a cooked CD TEXT format or come up with a way to allow raw lead-in data to be included.
The MODE=4 data in the lead-in area is what people usually mean when they talk about CD TEXT. This is where album and track information, copy protection status, “second TOC” information, etc. is stored.
The MODE=2 CD TEXT data consists of interactive text transmission system (ITTS, IEC61866) packets. It isn’t used as frequently or supported by as many players.
fwiw CD TEXT seems displayed by PC-8801MC CD player (defaults to CD PLAYER 88 if not found, screen visible by clicking on PR0):
