[Development] RFC: Speech Recognition API

[Tuomas Tuononen]

Hi all,

We are developing a new QtSpeechRecognition API for Qt.
The initial stage of development starts to be ready and we would like to 
get feedback from the Qt development list experts.

You can find the sources in review in qtspeech project, branch 
wip/speech-recognition:
https://codereview.qt-project.org/#/q/project:qt/qtspeech+branch:wip/speech-recognition,n,z

The initial implementation was already merged into 
wip/speech-recognition, but is still open for discussion.

Main features:
- Speech recognition engines are loaded as plug-ins.
- Engine is controlled asynchronously, causing only minimal load to the 
application thread.
- Built-in task queue makes plug-in development easier and forces 
unified behavior between engine integrations.
- Engine integration handles the audio recording, making it easy to use 
from the application.
- Application can create multiple grammars and switch between them.
- Setting mute temporarily disables speech recognition, allowing 
co-operation with audio output (speech prompts or audio cues).
- Includes integration to PocketSphinx engine (latest codebase) as a 
reference.

Current limitations:
- The recognition control only supports manual start/stop of audio 
recording.
- Only supports reading the grammars and dictionaries from files.
- The grammar and dictionary formats are engine-specific.
- Only transcription of what was said is returned (locale-specific).
- Switching the grammar always aborts current session.

Other notes:
- QML API probably needs improvement, as I'm not an expert in that area. 
Maybe an extra QML plug-in layer?

Future development:
1) Support for automatic endpointing (auto-stop) and continuously 
listening grammars.
2) Engine-independent run-time grammar API (support for updating the 
whole grammar or only part of the grammar).
3) Support for adding words to the dictionary run-time (probably with 
engine-specific phonetic data).
4) Support for switching the grammar without interrupting audio 
recording (e.g. switching from wake-up grammar to command grammar).
5) Engine-independent grammar file format.
6) Support for locale-independent results (grammar meta-data).

Best Regards,

Tuomas Tuononen,
Senior Software Engineer,
Code-Q Oy