7f8ddfb87f
./: overview docs R=katie@chromium.org platform-specific accessibility browser: docs pertaining to Chrome browser e.g. web contents and os: docs pertaining to Chrome OS Change-Id: I8b0423503d3199b10c8038e6cb45435558db1461 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3255169 Commit-Queue: David Tseng <dtseng@chromium.org> Reviewed-by: Katie Dektar <katie@chromium.org> Cr-Commit-Position: refs/heads/main@{#936992}
79 lines
2.9 KiB
Markdown
79 lines
2.9 KiB
Markdown
# Text to Speech in Chrome and Chrome OS
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Chrome and Chrome OS allow developers to produce synthesized speech. This
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document is an overview of the relevant code and code structure around
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synthesized speech.
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## Code structure
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A brief outline of the flow from speech request to the resulting speech on any
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platform.
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### Input
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- chrome.tts extension API
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- The [chrome.tts extension API](https://developer.chrome.com/apps/tts)
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allows extensions to request speech across Windows, Mac or Chrome OS, using
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native speech synthesis.
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- Input to the extension is first processed in the
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[TtsExtensionApi](https://cs.chromium.org/chromium/src/chrome/browser/speech/extension_api/tts_extension_api.h).
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- The extension is passed an [Options object](https://developer.chrome.com/apps/tts#method-speak)
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in chrome.tts.speak, which is translated into a
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[tts_controller Utterance](https://cs.chromium.org/chromium/src/content/public/browser/tts_controller.h?dr=CSs&l=120).
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- Web Speech API
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- Chrome implements
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[Window.SpeechSynthesis](https://developer.mozilla.org/en-US/docs/Web/API/Window/speechSynthesis)
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from the [Web Speech API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Speech_API).
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This allows web apps to do text-to-speech via the device's speech
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synthesizer.
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- A [WebSpeechSynthesisUtterance](https://cs.chromium.org/chromium/src/third_party/blink/public/platform/web_speech_synthesis_utterance.h)
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is created by window.SpeechSynthesis
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### Processing
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- The [TtsControllerImpl](https://cs.chromium.org/chromium/src/content/browser/speech/tts_controller_impl.h)
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(in content/) processes utterances and sends them to the correct output engine.
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- The [TtsControllerDelegateImpl](https://cs.chromium.org/chromium/src/chrome/browser/speech/tts_controller_delegate_impl.h)
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(in chrome/) provides chrome OS specific functionality.
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### Output
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- May differ by system, including Mac, Wind, Android, Arc++, and Chrome OS
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- Platform APIs are in [content/browser/speech](https://cs.chromium.org/chromium/src/content/browser/speech/), expect for
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Chrome OS's, which is in [chrome/browser/speech](https://cs.chromium.org/chromium/src/chrome/browser/speech/).
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- In Chrome OS:
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- [TtsEngineExtensionAPI](https://cs.chromium.org/chromium/src/chrome/browser/speech/extension_api/tts_engine_extension_api.h)
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forwards speech events to PATTS, or the network speech engine, or,
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coming soon, third-party speech engines.
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- [PATTS](../os/patts.md) is the built-in Chrome OS text-to-speech engine.
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### Testing
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- Unit tests
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- TtsControllerUnittest in content/browser/speech
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- TtsControllerDelegateImplUnittest in chrome/browser/speech
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- ArcTtsServiceUnittest for ARC++ voices
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- Browser tests
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- TtsApiTest tests Chrome TTS extension APIs
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- Fuzzer
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- In content_unittests, content/browser/speech/tts_platform_fuzzer.cc
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(currently Windows only).
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