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| 1 <p id="classSummary"> | |
| 2 Use the <code>chrome.ttsEngine</code> module to | |
| 3 implement a text-to-speech (TTS) engine using an extension. If your | |
| 4 extension registers using this API, it will receive events containing | |
| 5 an utterance to be spoken and other parameters when any extension or packaged | |
| 6 app uses the | |
| 7 <a href="tts.html">tts</a> | |
| 8 module to generate speech. Your extension can then use any available | |
| 9 web technology to synthesize and output the speech, and send events back | |
| 10 to the calling function to report the status. | |
| 11 </p> | |
| 12 <h2 id="overview">Overview</h2> | |
| 13 <p>An extension can register itself as a speech engine. By doing so, it | |
| 14 can intercept some or all calls to functions such as | |
| 15 <a href="tts.html#method-speak"><code>speak()</code></a> and | |
| 16 <a href="tts.html#method-stop"><code>stop()</code></a> | |
| 17 and provide an alternate implementation. | |
| 18 Extensions are free to use any available web technology | |
| 19 to provide speech, including streaming audio from a server, HTML5 audio, | |
| 20 Native Client, or Flash. An extension could even do something different | |
| 21 with the utterances, like display closed captions in a pop-up window or | |
| 22 send them as log messages to a remote server.</p> | |
| 23 <h2 id="manifest">Manifest</h2> | |
| 24 <p>To implement a TTS engine, an extension must | |
| 25 declare the "ttsEngine" permission and then declare all voices | |
| 26 it provides in the extension manifest, like this:</p> | |
| 27 <pre>{ | |
| 28 "name": "My TTS Engine", | |
| 29 "version": "1.0", | |
| 30 <b>"permissions": ["ttsEngine"], | |
| 31 "tts_engine": { | |
| 32 "voices": [ | |
| 33 { | |
| 34 "voice_name": "Alice", | |
| 35 "lang": "en-US", | |
| 36 "gender": "female", | |
| 37 "event_types": ["start", "marker", "end"] | |
| 38 }, | |
| 39 { | |
| 40 "voice_name": "Pat", | |
| 41 "lang": "en-US", | |
| 42 "event_types": ["end"] | |
| 43 } | |
| 44 ] | |
| 45 },</b> | |
| 46 "background_page": "background.html", | |
| 47 }</pre> | |
| 48 <p>An extension can specify any number of voices.</p> | |
| 49 <p>The <code>voice_name</code> parameter is required. The name should be | |
| 50 descriptive enough that it identifies the name of the voice and the | |
| 51 engine used. In the unlikely event that two extensions register voices | |
| 52 with the same name, a client can specify the ID of the extension that | |
| 53 should do the synthesis.</p> | |
| 54 <p>The <code>gender</code> parameter is optional. If your voice corresponds | |
| 55 to a male or female voice, you can use this parameter to help clients | |
| 56 choose the most appropriate voice for their application.</p> | |
| 57 <p>The <code>lang</code> parameter is optional, but highly recommended. | |
| 58 Almost always, a voice can synthesize speech in just a single language. | |
| 59 When an engine supports more than one language, it can easily register a | |
| 60 separate voice for each language. Under rare circumstances where a single | |
| 61 voice can handle more than one language, it's easiest to just list two | |
| 62 separate voices and handle them using the same logic internally. However, | |
| 63 if you want to create a voice that will handle utterances in any language, | |
| 64 leave out the <code>lang</code> parameter from your extension's manifest.</p> | |
| 65 <p>Finally, the <code>event_types</code> parameter is required if the engine can | |
| 66 send events to update the client on the progress of speech synthesis. | |
| 67 At a minimum, supporting the <code>'end'</code> event type to indicate | |
| 68 when speech is finished is highly recommended, otherwise Chrome cannot | |
| 69 schedule queued utterances.</p> | |
| 70 <p class="note"> | |
| 71 <strong>Note:</strong> If your TTS engine does not support | |
| 72 the <code>'end'</code> event type, Chrome cannot queue utterances | |
| 73 because it has no way of knowing when your utterance has finished. To | |
| 74 help mitigate this, Chrome passes an additional boolean <code>enqueue</code> | |
| 75 option to your engine's onSpeak handler, giving you the option of | |
| 76 implementing your own queueing. This is discouraged because then | |
| 77 clients are unable to queue utterances that should get spoken by different | |
| 78 speech engines.</p> | |
| 79 <p>The possible event types that you can send correspond to the event types | |
| 80 that the <code>speak()</code> method receives:</p> | |
| 81 <ul> | |
| 82 <li><code>'start'</code>: The engine has started speaking the utterance. | |
| 83 <li><code>'word'</code>: A word boundary was reached. Use | |
| 84 <code>event.charIndex</code> to determine the current speech | |
| 85 position. | |
| 86 <li><code>'sentence'</code>: A sentence boundary was reached. Use | |
| 87 <code>event.charIndex</code> to determine the current speech | |
| 88 position. | |
| 89 <li><code>'marker'</code>: An SSML marker was reached. Use | |
| 90 <code>event.charIndex</code> to determine the current speech | |
| 91 position. | |
| 92 <li><code>'end'</code>: The engine has finished speaking the utterance. | |
| 93 <li><code>'error'</code>: An engine-specific error occurred and | |
| 94 this utterance cannot be spoken. | |
| 95 Pass more information in <code>event.errorMessage</code>. | |
| 96 </ul> | |
| 97 <p>The <code>'interrupted'</code> and <code>'cancelled'</code> events are | |
| 98 not sent by the speech engine; they are generated automatically by Chrome.</p> | |
| 99 <p>Text-to-speech clients can get the voice information from your | |
| 100 extension's manifest by calling | |
| 101 <a href="tts.html#method-getVoices">getVoices()</a>, | |
| 102 assuming you've registered speech event listeners as described below.</p> | |
| 103 <h2 id="handling_speech_events">Handling speech events</h2> | |
| 104 <p>To generate speech at the request of clients, your extension must | |
| 105 register listeners for both <code>onSpeak</code> and <code>onStop</code>, | |
| 106 like this:</p> | |
| 107 <pre>var speakListener = function(utterance, options, sendTtsEvent) { | |
| 108 sendTtsEvent({'event_type': 'start', 'charIndex': 0}) | |
| 109 // (start speaking) | |
| 110 sendTtsEvent({'event_type': 'end', 'charIndex': utterance.length}) | |
| 111 }; | |
| 112 var stopListener = function() { | |
| 113 // (stop all speech) | |
| 114 }; | |
| 115 chrome.ttsEngine.onSpeak.addListener(speakListener); | |
| 116 chrome.ttsEngine.onStop.addListener(stopListener);</pre> | |
| 117 <p class="warning"> | |
| 118 <b>Important:</b> | |
| 119 If your extension does not register listeners for both | |
| 120 <code>onSpeak</code> and <code>onStop</code>, it will not intercept any | |
| 121 speech calls, regardless of what is in the manifest.</p> | |
| 122 <p>The decision of whether or not to send a given speech request to an | |
| 123 extension is based solely on whether the extension supports the given voice | |
| 124 parameters in its manifest and has registered listeners | |
| 125 for <code>onSpeak</code> and <code>onStop</code>. In other words, | |
| 126 there's no way for an extension to receive a speech request and | |
| 127 dynamically decide whether to handle it.</p> | |
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Chromium Code Reviews
Issue 10750017:
Extensions Docs Server: Intro data source (Closed)
Base URL: svn://svn.chromium.org/chrome/trunk/src