Sorry, no. I checked. This is from the Standard Additions Guide:
When a file is opened the file marker is set to the beginning. Subsequent read/write commands will move the marker, until it is closed. When opened again the file marker is reinitialised.
To append you must always use the 2nd M.O., or issue multiple write commands without closing between writes.
I’m not surprised.
I ran a small test on “Say hello” by April Wine (a band, not a female performer).
It opens in Text Edit, and on the last line is this readable text:
I could not paste that line, and had to type it: the board software did not think I had typed anything at all when I pasted it. The encoding of an mp3 file is nothing like plain text.
Are you surprised?
There still may be a text encoding issue. Typing text into the actual file presumably does retain the file’s encoding. Text written by AppleScript clearly uses a different encoding, as written text does not show up.
But I’m out of my depth here. Search this forum for ‘text encoding’. There may also be tutorials or guides in some other section.
Anyway, an mp3 file isn’t text, so it probably does not have the bits that can tell a script what encoding to use for writing.