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Bug 1256521 - Normalize speech rate in Windows. r=smaug

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MozReview-Commit-ID: EuQAqfoxwmo
This commit is contained in:
Eitan Isaacson 2016-03-14 19:03:40 -07:00
parent 7cb51cc5e3
commit 19dc2d2aab
1 changed files with 12 additions and 1 deletions
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13
dom/media/webspeech/synth/windows/SapiService.cpp
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@ -331,10 +331,21 @@ SapiService::Speak(const nsAString& aText, const nsAString& aUri,
if (FAILED(mSapiClient->SetVoice(voiceToken))) {
return NS_ERROR_FAILURE;
}
if (FAILED(mSapiClient->SetVolume(static_cast<USHORT>(aVolume * 100)))) {
return NS_ERROR_FAILURE;
}
if (FAILED(mSapiClient->SetRate(static_cast<long>(10 * log10(aRate))))) {
// The max supported rate in SAPI engines is 3x, and the min is 1/3x. It is
// expressed by an integer. 0 being normal rate, -10 is 1/3 and 10 is 3x.
// Values below and above that are allowed, but the engine may clip the rate
// to its maximum capable value.
// "Each increment between -10 and +10 is logarithmically distributed such
// that incrementing or decrementing by 1 is multiplying or dividing the
// rate by the 10th root of 3"
// https://msdn.microsoft.com/en-us/library/ee431826(v=vs.85).aspx
long rate = aRate != 0 ? static_cast<long>(10 * log10(aRate) / log10(3)) : 0;
if (FAILED(mSapiClient->SetRate(rate))) {
return NS_ERROR_FAILURE;
}