I installed Microsoft Speech Platform SDK 10.2, and I notice that sapi.dll and mssps.dll have similar APIs. What's the difference between them? Which one should I use? Thanks.
Microsoft Speech Platform SDK 10.2 is the server version of SAPI. The server engines support lower quality audio, but don't support dictation. Also, the server versions of SAPI (I believe) have license restrictions that the desktop versions do not.
The desktop engines are typically bundled with Windows, so if you have Vista or Windows 7, the desktop engine is built in; for XP, the desktop engine is free to use.