This issue came up for me using J River's Media Center 11, but I wonder if it is related to the MP3 spec and not a Media Center issue.

Background

I have created an extended tag in MC11, "bios" so artist bios can display in the excellent MC MultiInfo plugin (created by Cascius & DJ_Hazelwood). The tag type is "string" and "large value"

My main collection is stored on my desktop and mirrored to another networked PC, but I also have a copy of MC on my laptop, which is what I use to rip, do tag clean-up, etc. before moving the mp3 files over to the desktop's HD.

Consequently, in the Options menu, I've created a "bios" tag field on both the desktop and laptop copies of MC. The parameters are, as far as I can tell, identical, and the "include tag in file" box is checked on both.

I use MC's TagInfo function to enter the artist biography into the "bios" field for a particular album on the laptop, where it works as expected. However, it seems that when I copy the albums to the desktop, and import the new files into the desktop MC library, the bio information does not appear.

The Experiment

To try to determine if the issue was the info not being saved in the tag or the other copy of MC not reading the tag, I tried a little experiment. I tagged an album on the laptop, entering a rather long bio into the "bios" field and copied (using Windows Explorer) over to the desktop. The "bios" field showed as empty.

Then I copied the album back from the desktop to the laptop, reimported into the laptop MC, and lo and behold, the bio tag was empty. So it looked as though the problem was not that the desktop copy of MC was not reading the tag field created on the laptop, but that the information had not been written to the file.

Then I repeated this with an album whose bio was quite small, about the size of the largest paragraph in this post. In that case, the bio did appear in the desktop MC after transfer, so it evidently was stored in the file.

My question

From this I deduce that there is a maximum amount of information you can store in a single tag. Is this a result of the MP3 spec, or is it a result of the way MC11 works. If because of the MP3 spec, does anyone know what this amout is?

Thank you all

Well, an ID3v2 tag can have a maximum size 256MB (tag size is stored as a 32-bit "syncsafe" number, which means 28 usable bits, so it can be up to 2^28 = 268435456 bytes long. If you only have one frame in the tag, it can take up the entire thing if needed. So you could have an ID3v2 tag with only an image in it, and it can be 256MB large. (well, there is 10 bytes of overhead for frame headers and stuff, but that's basically right).

So i doubt that is the problem, though it is very possible your software can't recognize tags that large.

Thanks, Jebus. Is there software that will detect and read the tags? Or will the Media Center tag be visible only to MC? I seem to recall when I was fiddling with Foobar that it didn't recognize tags I'd created with another program, but never looked into why it was.

foobar does display tags created with other programs - itunes, helium, jriver etc, see the properties for any particular file.

Good to know about Foobar, it's been a while since I did anything with it.

I discovered the fix to my solution. If a bio (I'm using the ones at allmusic.com) contains a dash ( — ) it displays both in my tagging program (Tag & Rename) and MC11 as block character (a thick vertical line). A bio containing such a tag is not saved in the file. If I strip the "illegal" characters out, it does save.

UPDATE -

This appears to be a bug in Media Center, since MC will save text containing the dash characters in the Comment tag to the file.

Per the MC tagging scheme, my "bios" tag field is an "large value" string tag while the "comment" tag field is a "standard" string tag. I'm waiting to hear from the Media Center folks about the issue.