CHD CD images do not retain CD-TEXT data

[chungy]

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):

1. chdman createcd -i silent.toc -o silent.chd
2. chdman 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.

silent.zip

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. :-)

[ajrhacker]

Is this a specific case of the known issue of the CHD-CD format failing to include subchannel information?

[cuavas]

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.