> There was even a way to pack an MP3 in a .wav file so it could play on Win31 players that didn't have native support for MP3, using Windows' codec instead.
As I recall, it was wasn't decompressed, the MP3 data was written into a WAV file with a RIFF header. There were situations where you had a decoder available, but couldn't get your app to recognize that MP3 files were audio.
Pack. WAV doesn't need to store header and raw PCM data (which it usually does though), it's just a container.