97 lines
3.4 KiB
Swift
97 lines
3.4 KiB
Swift
import AVFoundation
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import Speech
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/// The transcribing service that transcribes recorded audio into text on device.
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///
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/// The service writes the recorded audio into a temporary `.m4a` file and runs it through a `SpeechAnalyzer` with a `SpeechTranscriber`
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/// module, joining the finalized results into the returned text. The transcription happens in the locale given at initialization — or rather in the
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/// closest equivalent the transcriber supports. The speech model assets for that locale are downloaded and installed on first use; every
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/// transcription after that happens entirely offline.
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public struct AudioTranscribingService: TranscribingService {
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// MARK: Properties
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/// The locale of the spoken language to transcribe.
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private let locale: Locale
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// MARK: Initializers
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/// Creates an audio transcribing service for a locale.
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///
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/// - Parameter locale: The locale of the spoken language to transcribe. Defaults to the user's current locale.
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public init(
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locale: Locale = .current
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) {
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self.locale = locale
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}
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// MARK: Methods
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/// Transcribes the given recorded audio into text, deleting the temporary audio file when the transcription finishes.
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///
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/// - Parameter audio: The recorded audio to transcribe.
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/// - Returns: The transcription of the recorded audio.
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/// - Throws: ``AudioTranscribingError/localeNotSupported`` when the transcriber supports no equivalent of the service's locale,
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/// or any error thrown while installing the speech model assets, reading the audio file, or analyzing its contents.
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public func transcribe(
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_ audio: Data
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) async throws -> String {
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try audio.write(to: Constant.File.url)
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defer {
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try? FileManager.default.removeItem(at: Constant.File.url)
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}
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guard let locale = await SpeechTranscriber.supportedLocale(
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equivalentTo: locale
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) else {
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throw AudioTranscribingError.localeNotSupported
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}
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let transcriber = SpeechTranscriber(
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locale: locale,
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preset: .transcription
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)
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if let request = try await AssetInventory.assetInstallationRequest(supporting: [transcriber]) {
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try await request.downloadAndInstall()
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}
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let analyzer = SpeechAnalyzer(modules: [transcriber])
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async let text = transcriber.results.reduce(into: "") { text, result in
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text += String(result.text.characters)
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}
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let file = try AVAudioFile(forReading: Constant.File.url)
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if let lastSampleTime = try await analyzer.analyzeSequence(from: file) {
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try await analyzer.finalizeAndFinish(through: lastSampleTime)
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} else {
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await analyzer.cancelAndFinishNow()
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}
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return try await text
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}
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}
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// MARK: - Errors
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/// The errors thrown by ``AudioTranscribingService``.
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public enum AudioTranscribingError: Error {
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/// The transcriber supports no equivalent of the locale the service was created with.
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case localeNotSupported
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}
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// MARK: - Constants
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/// The constant values used across the audio transcribing service.
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private enum Constant {
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/// The file constants.
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enum File {
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/// The location of the temporary file the recorded audio is written into for the analysis.
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static let url = FileManager.default.temporaryDirectory.appending(path: "transcription.m4a")
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}
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}
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