Speech API (Speech Application Programming Interface) or SAPI is a powerful speech-based interfaces API developed by Microsoft to allow the use of speech recognition and speech synthesis within Windows applications. To date a number of versions of the API have been released, which have shipped either as part of a Speech SDK, or as part of the Windows OS itself. Applications that use SAPI include Microsoft Office, Microsoft Agent and Microsoft Speech Server.
In general all versions of the API have been designed such that a software developer can write an application to perform speech recognition and synthesis by using a standard set of interfaces, accessible from a variety of programming languages. In addition, it is possible for a 3rd-party company to produce their own Speech Recognition and Text-To-Speech engines or adapt existing engines to work with SAPI. In principle, as long as these engines conform to the defined interfaces they can be used instead of the Microsoft-supplied engines.
SAPI 4.0 was released in 1998. This was shipped as part of an SDK that included recognition and synthesis engines. It also shipped (with synthesis engines only) in Windows 2000.
SAPI 5.1 version shipped in late 2001 as part of the Speech SDK version 5.1. This version of the API and TTS engines was shipped in Windows XP. This API was also shipped, together with a substantially improved version 6 recognition engine in Office 2003 and Windows XP Tablet PC Edition.
Most versions of Windows come with either SAPI4 or SAPI5 installed already, but this is not always the case. There are times when you may need to install one or both of these on your computer in order to allow Text To Speech programs to work, or to take advantage of some features.
- You can now use the Win32 Speech API (SAPI) to develop speech applications with Visual Basic ®, ECMAScript and other Automation languages.
- The SDK also includes freely distributable text-to-speech (TTS) engines (in U.S. English and Simplified Chinese) and speech recognition (SR) engines (in U.S. English, Simplified Chinese, and Japanese).