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| 1 <p id="classSummary"> | |
| 2 Use the <code>chrome.experimental.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="experimental.tts.html">experimental.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 | |
| 13 <p class="note"><b>Give us feedback:</b> If you have suggestions, | |
| 14 especially changes that should be made before stabilizing the first | |
| 15 version of this API, please send your ideas to the | |
| 16 <a href="http://groups.google.com/a/chromium.org/group/chromium-extensions">chro
mium-extensions</a> | |
| 17 group.</p> | |
| 18 | |
| 19 <h2 id="overview">Overview</h2> | |
| 20 | |
| 21 <p>To enable this experimental API, visit | |
| 22 <b>chrome://flags</b> and enable <b>Experimental Extension APIs</b>. | |
| 23 | |
| 24 <p>An extension can register itself as a speech engine. By doing so, it | |
| 25 can intercept some or all calls to functions such as | |
| 26 <a href="experimental.tts.html#method-speak"><code>speak()</code></a> and | |
| 27 <a href="experimental.tts.html#method-stop"><code>stop()</code></a> | |
| 28 and provide an alternate implementation. | |
| 29 Extensions are free to use any available web technology | |
| 30 to provide speech, including streaming audio from a server, HTML5 audio, | |
| 31 Native Client, or Flash. An extension could even do something different | |
| 32 with the utterances, like display closed captions in a pop-up window or | |
| 33 send them as log messages to a remote server.</p> | |
| 34 | |
| 35 <h2 id="manifest">Manifest</h2> | |
| 36 | |
| 37 <p>To implement a TTS engine, an extension must first declare all voices | |
| 38 it provides in the extension manifest, like this:</p> | |
| 39 | |
| 40 <pre>{ | |
| 41 "name": "My TTS Engine", | |
| 42 "version": "1.0", | |
| 43 <b>"permissions": ["experimental"], | |
| 44 "tts_engine": { | |
| 45 "voices": [ | |
| 46 { | |
| 47 "voice_name": "Alice", | |
| 48 "lang": "en-US", | |
| 49 "gender": "female", | |
| 50 "event_types": ["start", "marker", "end"] | |
| 51 }, | |
| 52 { | |
| 53 "voice_name": "Pat", | |
| 54 "lang": "en-US", | |
| 55 "event_types": ["end"] | |
| 56 } | |
| 57 ] | |
| 58 },</b> | |
| 59 "background_page": "background.html", | |
| 60 }</pre> | |
| 61 | |
| 62 <p>An extension can specify any number of voices.</p> | |
| 63 | |
| 64 <p>The <code>voice_name</code> parameter is required. The name should be | |
| 65 descriptive enough that it identifies the name of the voice and the | |
| 66 engine used. In the unlikely event that two extensions register voices | |
| 67 with the same name, a client can specify the ID of the extension that | |
| 68 should do the synthesis.</p> | |
| 69 | |
| 70 <p>The <code>gender</code> parameter is optional. If your voice corresponds | |
| 71 to a male or female voice, you can use this parameter to help clients | |
| 72 choose the most appropriate voice for their application.</p> | |
| 73 | |
| 74 <p>The <code>lang</code> parameter is optional, but highly recommended. | |
| 75 Almost always, a voice can synthesize speech in just a single language. | |
| 76 When an engine supports more than one language, it can easily register a | |
| 77 separate voice for each language. Under rare circumstances where a single | |
| 78 voice can handle more than one language, it's easiest to just list two | |
| 79 separate voices and handle them using the same logic internally. However, | |
| 80 if you want to create a voice that will handle utterances in any language, | |
| 81 leave out the <code>lang</code> parameter from your extension's manifest.</p> | |
| 82 | |
| 83 <p>Finally, the <code>event_types</code> parameter is required if the engine can | |
| 84 send events to update the client on the progress of speech synthesis. | |
| 85 At a minimum, supporting the <code>'end'</code> event type to indicate | |
| 86 when speech is finished is highly recommended, otherwise Chrome cannot | |
| 87 schedule queued utterances.</p> | |
| 88 | |
| 89 <p class="note"> | |
| 90 <strong>Note:</strong> If your TTS engine does not support | |
| 91 the <code>'end'</code> event type, Chrome cannot queue utterances | |
| 92 because it has no way of knowing when your utterance has finished. To | |
| 93 help mitigate this, Chrome passes an additional boolean <code>enqueue</code> | |
| 94 option to your engine's onSpeak handler, giving you the option of | |
| 95 implementing your own queueing. This is discouraged because then | |
| 96 clients are unable to queue utterances that should get spoken by different | |
| 97 speech engines.</p> | |
| 98 | |
| 99 <p>The possible event types that you can send correspond to the event types | |
| 100 that the <code>speak()</code> method receives:</p> | |
| 101 | |
| 102 <ul> | |
| 103 <li><code>'start'</code>: The engine has started speaking the utterance. | |
| 104 <li><code>'word'</code>: A word boundary was reached. Use | |
| 105 <code>event.charIndex</code> to determine the current speech | |
| 106 position. | |
| 107 <li><code>'sentence'</code>: A sentence boundary was reached. Use | |
| 108 <code>event.charIndex</code> to determine the current speech | |
| 109 position. | |
| 110 <li><code>'marker'</code>: An SSML marker was reached. Use | |
| 111 <code>event.charIndex</code> to determine the current speech | |
| 112 position. | |
| 113 <li><code>'end'</code>: The engine has finished speaking the utterance. | |
| 114 <li><code>'error'</code>: An engine-specific error occurred and | |
| 115 this utterance cannot be spoken. | |
| 116 Pass more information in <code>event.errorMessage</code>. | |
| 117 </ul> | |
| 118 | |
| 119 <p>The <code>'interrupted'</code> and <code>'cancelled'</code> events are | |
| 120 not sent by the speech engine; they are generated automatically by Chrome.</p> | |
| 121 | |
| 122 <p>Text-to-speech clients can get the voice information from your | |
| 123 extension's manifest by calling | |
| 124 <a href="experimental.tts.html#method-getVoices">getVoices()</a>, | |
| 125 assuming you've registered speech event listeners as described below.</p> | |
| 126 | |
| 127 <h2 id="handling_speech_events">Handling speech events</h2> | |
| 128 | |
| 129 <p>To generate speech at the request of clients, your extension must | |
| 130 register listeners for both <code>onSpeak</code> and <code>onStop</code>, | |
| 131 like this:</p> | |
| 132 | |
| 133 <pre>var speakListener = function(utterance, options, sendTtsEvent) { | |
| 134 sendTtsEvent({'event_type': 'start', 'charIndex': 0}) | |
| 135 | |
| 136 // (start speaking) | |
| 137 | |
| 138 sendTtsEvent({'event_type': 'end', 'charIndex': utterance.length}) | |
| 139 }; | |
| 140 | |
| 141 var stopListener = function() { | |
| 142 // (stop all speech) | |
| 143 }; | |
| 144 | |
| 145 chrome.experimental.ttsEngine.onSpeak.addListener(speakListener); | |
| 146 chrome.experimental.ttsEngine.onStop.addListener(stopListener);</pre> | |
| 147 | |
| 148 <p class="warning"> | |
| 149 <b>Important:</b> | |
| 150 If your extension does not register listeners for both | |
| 151 <code>onSpeak</code> and <code>onStop</code>, it will not intercept any | |
| 152 speech calls, regardless of what is in the manifest.</p> | |
| 153 | |
| 154 <p>The decision of whether or not to send a given speech request to an | |
| 155 extension is based solely on whether the extension supports the given voice | |
| 156 parameters in its manifest and has registered listeners | |
| 157 for <code>onSpeak</code> and <code>onStop</code>. In other words, | |
| 158 there's no way for an extension to receive a speech request and | |
| 159 dynamically decide whether to handle it.</p> | |
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Chromium Code Reviews
Issue 7258007:
Move the tts and ttsEngine APIs out of experimental, and give (Closed)
Base URL: svn://chrome-svn/chrome/trunk/src/