I do not understand what I see when I view the metadata in a Vorbis commented FLAC file using a hex editor application such as HxD.
First of all, media players and mp3tag seem to always display the correct values for Vorbis comments that we've added to FLAC files. There's no obvious problem there.
What I find confusing is the fact that when I wish to view the Vorbis comments using a hex editor, I occasionally find characters that don't belong there but also do not show up when viewed with mp3tag or applications like JRiver Media Center.
If you look at the attached PNG screenshot, you will see the letter D (ASCII 44) at position 177 in the file but it is not valid part of the tag nor is it displayed as such. The same is true for the # symbol at address 1BF. The # symbol is clearly not part of the FLAC codec's version number and it is not reported as such.
I understand that the character set used to enter the value of a Vorbis comment's field is supposed to be UTF-8 compliant, but beyond that I am at a loss to understand why, for example, the ASCII 44 character is there but doesn't show up when the tag is read by an application. Apparently mp3tag and other applications seem to know what is legitimate and what is not.
Is there a simple explanation that would remove my confusion, or do I need to earn a PhD in computer science?
Thanks in advance for any explanation that removes my ignorance on this topic. I'm too old to go back to the University.