Unclear interimResults Web Speech API implementation in Safari iOS (WebKit) #120

Hi all!

I have been working on a web speech recognition service using the Web Speech API. This service is intended to work on smartphones, primarily Chrome on Android and Safari (or WebKit WebView) on iOS.

In my specific use case, I need to set the properties continuous = true and interimResults = true. However, I have noticed that interimResults = true does not always work as expected in WebKit.

I understand that this setting should provide fast, native, on-device speech recognition with isFinal = false. However, at times, the recognition becomes throttled and slow, yielding isFinal = true and switching to cloud-based recognition.

To confirm whether the recognition is cloud-based, I tested it by disabling the internet connection before starting speech recognition. In some cases, recognition fails entirely, which suggests that requiresOnDeviceRecognition = false is being applied. (Reference: SFSpeechRecognitionRequest.requiresOnDeviceRecognition)

I believe this is not the expected behavior when setting interimResults = true. I have researched the native services used by the Web Speech API on iOS devices, and the following links seem relevant:
• SFSpeechRecognizer
• SFSpeechRecognitionRequest.shouldReportPartialResults
• SFSpeechRecognizer.supportsOnDeviceRecognition
• Recognizing speech in live audio
• Apple Developer Forums Discussion

I found that setRequiresOnDeviceRecognition and setShouldReportPartialResults appear to be set correctly, but apparently, they do not work as expected:
WebKit Source Code