In ID3 tags there's such a thing as unsynchronization: the MP3 syncword is 11 bits set to one so for the tag data not to be mistaken for an MPR3 frame it must n

In ID3 tags there's such a thing as unsynchronization: the MP3 syncword is 11 bits set to one so for the tag data not to be mistaken for an MPR3 frame it must not have a similar sequence of bits. The solution was to replace every 0xFF in tag data with 0xFF 0x00. Or not to replace, as this mistake may only be made by old players that do not understand ID3. So there's a special setting for this that may occur in two places: in the whole tag or in an individual frame within a tag. The logic itself is simple, as you read data byte-by-byte you need to check check if the previous byte was 0xFF and the frame or tag is marked as unsychronized. Yet it's not that simple to describe this declaratively. I wonder if Kaitai can actually do this. From what I see Kaitai does have at least part of ID3 described, but it doesn't seem to actually do unsynchronization, as far as I can tell from the code.