According to http://www.garykessler.net/library/file_sigs.html . If this ID3 signature is not found, it could be an untagged mp3 file. The following configuration is used in magic.mime file to determine untagged mp3 file to assume that it's an MP3.
0 beshort &0xffe0
2 ubyte&0xF0 >0x0F
2 ubyte&0xF0 <0xE1 audio/mpeg
Here is the block of code to determine where "ubyte" datatype is missed to return
private int getType(String tok) {
if (tok.startsWith("string")) {
return STRING_TYPE;
} else if (tok.startsWith("belong")) {
return BELONG_TYPE;
} else if (tok.equals("short")) {
return SHORT_TYPE;
} else if (tok.startsWith("lelong")) {
return LELONG_TYPE;
} else if (tok.startsWith("beshort")) {
return BESHORT_TYPE;
} else if (tok.startsWith("leshort")) {
return LESHORT_TYPE;
} else if (tok.equals("byte")) {
return BYTE_TYPE;
}
return UNKNOWN_TYPE;
}
Therefore, MimeUtil returning unknown type for "untagged MP3"