FRMT contains the WAV format description of an iMUS chunk, that is the samplerate, number of channels etc. Actually, FRMT works as a hook (just as JUMP, REGN etc.), i.e. it has a been given a position inside the WAV DATA (which is usually at the start of the data).

"FRMT"	dword	Block identifier
dwSize	dword	Size in bytes (BE)
dwPosition	dword	Hook position.
dwUnknown	dword	Unknown
dwBitsPerSample	dword	Bits per sample - usually 12 or 16.
dwSampleRate	dword	Samplerate in hz - usually 11025 or 22050.
nChannels	dword	Number of channels - 1 = mono, 2 = stereo.