chrome.ttsEngine
Description: |
Use the chrome.ttsEngine API to implement a text-to-speech(TTS) engine using an extension. If your extension registers using this API, it will receive events containing an utterance to be spoken and other parameters when any extension or Chrome App uses the tts API to generate speech. Your extension can then use any available web technology to synthesize and output the speech, and send events back to the calling function to report the status.
|
Availability: |
Since Chrome 35.
|
Permissions: |
"ttsEngine"
|
Overview
An extension can register itself as a speech engine. By doing so, it can intercept some or all calls to functions such as tts.speak and tts.stop and provide an alternate implementation. Extensions are free to use any available web technology to provide speech, including streaming audio from a server, HTML5 audio, Native Client, or Flash. An extension could even do something different with the utterances, like display closed captions in a pop-up window or send them as log messages to a remote server.
Manifest
To implement a TTS engine, an extension must declare the "ttsEngine" permission and then declare all voices it provides in the extension manifest, like this:
{ "name": "My TTS Engine", "version": "1.0", "permissions": ["ttsEngine"], "tts_engine": { "voices": [ { "voice_name": "Alice", "lang": "en-US", "event_types": ["start", "marker", "end"] }, { "voice_name": "Pat", "lang": "en-US", "event_types": ["end"] } ] }, "background": { "page": "background.html", "persistent": false } }
An extension can specify any number of voices.
Once loaded, an extension can replace the list of declared voices
by calling chrome.ttsEngine.updateVoices
The voice_name
parameter is required. The name should be
descriptive enough that it identifies the name of the voice and the
engine used. In the unlikely event that two extensions register voices
with the same name, a client can specify the ID of the extension that
should do the synthesis.
The lang
parameter is optional, but highly recommended.
Almost always, a voice can synthesize speech in just a single language.
When an engine supports more than one language, it can easily register a
separate voice for each language. Under rare circumstances where a single
voice can handle more than one language, it's easiest to just list two
separate voices and handle them using the same logic internally. However,
if you want to create a voice that will handle utterances in any language,
leave out the lang
parameter from your extension's manifest.
Finally, the event_types
parameter is required if the engine can
send events to update the client on the progress of speech synthesis.
At a minimum, supporting the 'end'
event type to indicate
when speech is finished is highly recommended, otherwise Chrome cannot
schedule queued utterances.
Note: If your TTS engine does not support
the 'end'
event type, Chrome cannot queue utterances
because it has no way of knowing when your utterance has finished. To
help mitigate this, Chrome passes an additional boolean enqueue
option to your engine's onSpeak handler, giving you the option of
implementing your own queueing. This is discouraged because then
clients are unable to queue utterances that should get spoken by different
speech engines.
The possible event types that you can send correspond to the event types
that the speak()
method receives:
'start'
: The engine has started speaking the utterance.'word'
: A word boundary was reached. Useevent.charIndex
to determine the current speech position.'sentence'
: A sentence boundary was reached. Useevent.charIndex
to determine the current speech position.'marker'
: An SSML marker was reached. Useevent.charIndex
to determine the current speech position.'end'
: The engine has finished speaking the utterance.'error'
: An engine-specific error occurred and this utterance cannot be spoken. Pass more information inevent.errorMessage
.
The 'interrupted'
and 'cancelled'
events are
not sent by the speech engine; they are generated automatically by Chrome.
Text-to-speech clients can get the voice information from your extension's manifest by calling tts.getVoices, assuming you've registered speech event listeners as described below.
Handling speech events
To generate speech at the request of clients, your extension must
register listeners for both onSpeak
and onStop
,
like this:
var speakListener = function(utterance, options, sendTtsEvent) { sendTtsEvent({'event_type': 'start', 'charIndex': 0}) // (start speaking) sendTtsEvent({'event_type': 'end', 'charIndex': utterance.length}) }; var stopListener = function() { // (stop all speech) }; chrome.ttsEngine.onSpeak.addListener(speakListener); chrome.ttsEngine.onStop.addListener(stopListener);
Important:
If your extension does not register listeners for both
onSpeak
and onStop
, it will not intercept any
speech calls, regardless of what is in the manifest.
The decision of whether or not to send a given speech request to an
extension is based solely on whether the extension supports the given voice
parameters in its manifest and has registered listeners
for onSpeak
and onStop
. In other words,
there's no way for an extension to receive a speech request and
dynamically decide whether to handle it.
Summary
Types | |
---|---|
VoiceGender | |
Methods | |
updateVoices −
chrome.ttsEngine.updateVoices(array of tts.TtsVoice voices)
| |
Events | |
onSpeak | |
onStop | |
onPause | |
onResume |
Types
VoiceGender
Enum |
---|
"male" ,
or "female"
|
Methods
updateVoices
chrome.ttsEngine.updateVoices(array of tts.TtsVoice voices)
Since Chrome 66.
Called by an engine to update its list of voices. This list overrides any voices declared in this extension's manifest.
Parameters | ||
---|---|---|
array of tts.TtsVoice | voices |
Array of tts.TtsVoice objects representing the available voices for speech synthesis. |
Events
onSpeak
Called when the user makes a call to tts.speak() and one of the voices from this extension's manifest is the first to match the options object.
addListener
chrome.ttsEngine.onSpeak.addListener(function callback)
Parameters | ||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
function | callback |
The callback parameter should be a function that looks like this: function(string utterance, object options, function sendTtsEvent) {...};
|
onStop
Fired when a call is made to tts.stop and this extension may be in the middle of speaking. If an extension receives a call to onStop and speech is already stopped, it should do nothing (not raise an error). If speech is in the paused state, this should cancel the paused state.
addListener
chrome.ttsEngine.onStop.addListener(function callback)
Parameters | ||
---|---|---|
function | callback |
The callback parameter should be a function that looks like this: function() {...};
|
onPause
Optional: if an engine supports the pause event, it should pause the current utterance being spoken, if any, until it receives a resume event or stop event. Note that a stop event should also clear the paused state.
addListener
chrome.ttsEngine.onPause.addListener(function callback)
Parameters | ||
---|---|---|
function | callback |
The callback parameter should be a function that looks like this: function() {...};
|
onResume
Optional: if an engine supports the pause event, it should also support the resume event, to continue speaking the current utterance, if any. Note that a stop event should also clear the paused state.
addListener
chrome.ttsEngine.onResume.addListener(function callback)
Parameters | ||
---|---|---|
function | callback |
The callback parameter should be a function that looks like this: function() {...};
|