android-tts-server/README.md

What is it?

TTS Server is an Android-only application that provides a REST-based interface for on-board TTS engine of your device. The application is aimed on home automation and allows you to give a second life to your old smartphone, which can now act as a standalone, all-inclusive web TTS provider for your speech-based home notification system.

For what?

Android is provided with a great offline TTS engine for almost every language on the world. If you care about high availability of the web TTS provider or you don't want your notifications go through the Internet to the cloud providers, you can utilise your smartphone to done the job.

How does it work?

TTS Server runs a service with HTTP server that exposes endpoints allowing you to perform TTS task. As the Android implements its own process-killer, the application needs to run the service on the foreground (so the notification is always shown) keeping it alive and preventing it from being killed. Because of that, keep in mind that the application might drain your battery, so it is recommended to use it only on the devices being always connected to the power source.

Consuming REST interface

So far, the application provides two endpoints: /say, /wave, /sonos and /sonos/{fileName}. Each data-accepting endpoint works with JSON-based body, so each request carrying the data requires a proper Content-Type header.

The /say endpoint

POST /say
{
"text": "The text to be spoken",
"language": "en_US"
}

Returns: 200 OK with empty body

The /say endpoint allows you to perform TTS task using device's speakers or the external ones connected to it via jack, Bluetooth etc. For example if you have some old PC-speakers you are able to connect your device to them via line port and get a complete speech-based notification system.

The /{wave,acc,mp3,m4a,wma,flac} endpoint

POST /{wave,acc,mp3,m4a,wma,flac}
{
"text": "The text to be spoken",
"language": "en_US"
}

Returns: 200 OK with proper audio file

This endpoint enables you to download an audio file file containing speech of the provided text. The goal of this endpoint is to provide interface allowing you establishment of the connection between the TTS Server and some other kind of already running TTS system, which can invoke the HTTP request to your Android device and do something with returned audio file. Note that all files but wav originates right from the wav file through FFmpeg converter.

The /sonos endpoint

POST /sonos
{
    "text": "The text to be spoken",
    "language": "en_US",
    "zone": "Living room",
    "volume": 60
}

Returns: 202 Accepted meaning that the request has been queued and waits to be completed.

The /sonos endpoint enables you to use your Sonos devices as a TTS speakers. You need just to provide a text to be spoken and a desired zone name, where message is supposed to be spoken. In the contrast to other endpoints, the /sonos endpoint is non-blocking, which means your request is accepted and pushed at the end of queue, where you are immediately given with response. The message waits in the queue to be spoken protecting the Sonos device from messages race condition problem.

The /sonos/{fileName} endpoint

GET /sonos/{fileName}

Returns: 200 OK with wave file (Content-Type: audio/x-wav)

This endpoint is designed for serving synthesized wave files by /sonos endpoint to Sonos devices and is not intended to be used directly by you. After hitting the /sonos endpoint, requested message is synthesized to wave file which is being served through the /sonos/{fileName} endpoint and Sonos device is requested to change its source stream URL to this file. The already generated files are stored in cache directory so there is no need to resynthesize frequently-used message which reduces the overall time needed to complete the request. You are still able to invalidate this cache via application settings.

The /gong.wav endpoint

GET /gong.wav

Returns: 200 OK with gong wave file (Content-Type: audio/x-wav)

This endpoint is designed for serving gong wave to Sonos devices and – similar to /sonos/{fileName} – is not intended to be used directly by you. If gong is enabled in the settings, Sonos is requested to change its source stream URL to a gong file prior to the actual announcement being served by /sonos/{fileName} endpoint.