It seems like there's an ambiguity between the Byte Order Marks used for UTF16-LE and UTF-32LE. In particular, consider a file that contains the following 8 bytes:
FF FE 00 00 00 00 00 00
How can I tell if this file contains:
Unicode BOMs are described here: http://unicode.org/faq/utf_bom.html#bom4 but there's no discussion of this ambiguity. Am I missing something?
As the name suggests, the BOM only tells you the byte order, not the encoding. You have to know what the encoding is first, then you can use the BOM to determine whether the least or most significant bytes are first for multibyte sequences.
A fortunate side-effect of the BOM is that you can also sometimes use it to guess the encoding if you don't know it, but that is not what it was designed for and it is no substitute for sending proper encoding information.
It is unambiguous. FF FE is for UTF-16LE, and FF FE 00 00 denotes UTF-32LE. There is no reason to think that FF FE 00 00 is possibly UTF-16LE because the UTFs were designed for text, and users shouldn't be using NUL characters in their text. After all, when was the last time you opened a hex editor and inserted a few bytes of 00 into a text document? ^_^