Expand description
A simplified wrapper around Microsoft’s Speech API (SAPI) library.
Features
The goal of this crate is to expose a subset of SAPI features in a way that is easy to use in Rust. It does not aim to provide the full set of features SAPI offers. Since the focus is on relative ease of use (compared to dealing with COM directly) and simplicity of API, many SAPI features are missing in this crate.
Text-to-speech
The tts module provides the API to render text as a speech using one or more SAPI voices installed on the system.
To generate speech, you first need to create an instance of one of the available synthesizer types. Which synthesizer you choose will depend on whether you want to block the execution while the speech is synthesized or not.
You can configure the synthesizer to output to the default audio device, to a file, or to a memory buffer. You can control the synthesizer’s default speaking voice, rate of speech, and volume.
The speech you synthesize can be a simple string, or it can be a series of instructions controlling various aspects of the speech synthesis, such as voice, rate, volume, pitch, or pronunciation.
You can enumerate the installed voices and filter them by one or more of their characteristics (e.g. age or gender).
Speech recognition
The stt module provides the API to recognize speech, convert it to text, and annotate it with semantic tags.
The first thing you need is an instance of the recognition engine. Once created, you can configure it to listen to the default recording device, to read a file, or to read from a memory buffer. You can stop and resume recognition by disabling and enabling the recognizer.
To configure which spoken phrases the engine can recognize, you need to define one or more grammars. A grammar is a set of rules that define what word structures form recognizable phrases.
A grammar must be loaded into a recognition context before the engine can recognize the phrases in it. Which context type you choose will depend on whether you want to block the execution while waiting for a phrase to be recognized or not.
COM and Lifetime of SAPI Types
Microsoft SAPI is a COM library. All COM objects and interfaces use reference counting to control their lifetime. Many types in this crate wrap these COM objects. As such, when you drop an instance of one of these types, it doesn’t mean that the underlying COM object will be destroyed.
For example, if you have a Recognizer, a SyncContext,
and a Grammar, dropping the Recognizer while the SyncContext or the
Grammar are still alive will not destroy the underlying recognition engine with its
associated contexts and rules.
This crate does not currently represent these COM references using Rust lifetimes. This was a deliberate design decision to keep the API and the code as simple as possible.
Modules
Support for streaming audio to and from files and memory buffers.
Speech recognition API.
Support for async operations running on Tokio.
Text-to-speech API.
Functions
Deinitializes SAPI for the current thread. This function must be called for every thread that
called initialize(), the same number of times.
Initializes SAPI on the current thread. This function must be called for every thread that intends to use SAPI.