First, I'm still not convinced that the CD TOC contains any metadata (Album name, Artists, Track name, etc.). A quick Google is a little inconclusive as it only says what is in the TOC and not what is not in it, but
this page from MusicBrainz show what is in the TOC, and it isn't metadata.
MusicBrainz also says;
"The deeper stuff will be needed
in case the CD-Text format becomes popular, which stores extra data (like artist and track information) in the above mentioned control data parts."
The use of CD-Text to store additional metadata about the disc is the only place such data will be found on the disc, I believe. I don't think it has become popular, but I don't have a lot of recent discs to find out.
This tutorial describes where the TOC is, and what is in it. Which is;
"The TOC in the "lead-in" area contains the total length of the recording session, a list of tracks and their starting addresses and some other information."
No mention of metadata.
This one mentions a proposal to store a data track, which could hold some metadata, but its references to TOC are just the normal Track information. The TOC doesn't hold metadata, the Data Track does. If that was ever implemented.
I found lots of discussions about TOC identifying how many tracks are on a CD and where they start and end. But nothing about actual metadata. Album name, Artists, Track name, etc. So, if such metadata exists on a CD, it comes from the CD-Text file.
Do you have a or know of a tool that just reads the CD TOC, or the CD-Text file, and identifies where the data is coming from, and shows the metadata?
Or do you have a reference (Link) for a description of what is in the TOC for modern CDs?
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Regarding your tests;
Had MC ever seen that CD before?
As soon as you insert a CD and allow MC to look it up in the online database, MC creates a record in its internal CD Database. If you had CD Ripping and YADB Lookup turned off, but the CD had been seen before, MC just looked up its internal CD Database.
I tested this with an old Glenn Miller CD, with everything we've discussed turned off except the CD Ripping Feature. Using a View which is limited to Audio files and the CD Database, Glenn Miller didn't show up. The CD under "Drives & Devices" showed all "Unknowns". I clicked the "Update from Online Database" and the metadata was filled in under "Drives & Devices". Glenn Miller then showed in the CD Database View. I ejected the CD and the metadata still showed up. I restarted MC and the CD with all its metadata still showed up in the CD Database View. I then reinserted the CD and looked at it under "Drives & Devices". All the metadata was present, even though the online lookup is turned off.
Once MC has seen a CD, or any optical disc, it creates a CD Database record, and it will reuse that data later, as required.
So basically, if MC had seen this CD before, all your tests were invalid.
If MC had never seen this CD, then in your first test MC may have found the metadata in the "CDPlayer.ini" file on your PC. I believe MC will look that up even with the online lookup turned off.
Once you ran the "Update from Online Database" all following tests were invalid, unless you deleted the record from the CD Database, and deleted the same record from the Removed Database before any following test.
I don't think MC writes "CDPlayer.ini" files. It just reads them. I don't have any on my PC. Never have, despite many CD rips.