I just add this free little online tool for all the people interested what the DJ-Software "Traktor" saves inside his proprietary binary chunk inside a PRIV id3 tag.
If you save the few available metadata tags for a mp3 file in Traktor, it looks like this:
This is interesting, but, unfortunately, not useful.
Now - if, as well as being able to READ the PRIV4 tag, we could WRITE it (or, even just an indicator that there IS info in the PRIV4 tag) to an empty tag in the MP3 file, then it'd be useful...
This will not happen anytime soon, because of the proprietary (not public) structure of this PRIV tag. native-instruments.com does not seem to be interested in allowing third-party tools to manipulate their "own" id3 tag.
You may have already read it: "As you might have noticed, there is a check sum. And sure enough, changing even a single byte causes Traktor to completely ignore the data."
The necessary chechsum function has not been reverse engineered yet.
BTW: There is no such frame type name as PRIV4. Frame type names according to the id3.org standard are only 4 characters long and without any numbers. (There are a few frame names with a number at 4th - not 5th - position.)