Is it the nature of .ACM audio codecs that they work only with
files that start with a WAVEFORMATEX header?

In other words: must formats like MP3 and Ogg Vorbis and Speex
be encapsulated into a .WAV file for an .ACM codec to make sense
of them?

If this is so -- is there another audio codec standard for
Windows (a Microsoft standard or not) that does not require this?

Chris Giese wrote:
The microsoft solution is use DirectShow filters, for a new format you
would need a parser filter and a decoder, the decoder can be an ACM
codec if you like and it will contained by the ACM wrapper filter but
doesnt need to be.