The MSACM/MSACM32 keeps some data cached for all known ACM drivers. Under the key
Software\Microsoft\AudioCompressionManager\DriverCache\<driver name> |
aFormatTagCache which contains an array of DWORD. There are two DWORDs per cFormatTags entry. The first DWORD contains a format tag value, and the second the associated maximum size for a WAVEFORMATEX structure. (Fields dwFormatTag and cbFormatSize from ACMFORMATDETAILS)
cFilterTags contains the number of tags supported by the driver for filtering.
cFormatTags contains the number of tags support by the driver for conversions.
fdwSupport (the same as the one returned from acmDriverDetails).
The cFilterTags, cFormatTags, fdwSupport are the same values as the ones returned from acmDriverDetails function.