speech-recognition

# Speech Recognition

Transcribe live and pre-recorded audio to text using Apple's Speech framework.
Covers `SpeechAnalyzer` / `SpeechTranscriber` (iOS 26+) and
`SFSpeechRecognizer` (iOS 10+). Targets Swift 6.3 / iOS 26+ while preserving
fallback guidance for apps that support older OS versions.

**Scope boundary:** Use this skill for speech-to-text recognition, speech
authorization, microphone capture plumbing, and result handling. Hand off text
analysis, language identification after transcription, sentiment, embeddings,
and translation to `natural-language`; hand off audio playback UI to `avkit`;
hand off summarization or generation over transcripts to `apple-on-device-ai`.

## Contents

- [SpeechAnalyzer Strategy (iOS 26+)](#speechanalyzer-strategy-ios-26)
- [SFSpeechRecognizer Setup](#sfspeechrecognizer-setup)
- [Authorization](#authorization)
- [Live Microphone Transcription](#live-microphone-transcription)
- [Pre-Recorded Audio File Recognition](#pre-recorded-audio-file-recognition)
- [On-Device vs Server Recognition](#on-device-vs-server-recognition)
- [Handling Results](#handling-results)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## SpeechAnalyzer Strategy (iOS 26+)

Use `SpeechAnalyzer` for modern iOS 26+ speech analysis, especially long-form
recordings, live transcription, time-indexed transcripts, and fully on-device
flows. Keep `SFSpeechRecognizer` for iOS 10+ deployment targets, server-backed
locale coverage, or existing callback/delegate implementations.

Read [SpeechAnalyzer patterns](references/speechanalyzer-patterns.md) when
implementing an iOS 26+ transcription pipeline, model asset handling, volatile
results, or file/buffer examples.

### SpeechAnalyzer setup checklist

1. Choose the module:
   - `SpeechTranscriber` for the newer general-purpose on-device model.
   - `DictationTranscriber` when `SpeechTranscriber` is unavailable for the
     current device or locale and dictation-compatible support is acceptable.
   - `SpeechDetector` only in conjunction with a transcriber when voice
     activity detection is worth the accuracy/power tradeoff.
2. Check support before creating the session:
   - `SpeechTranscriber.isAvailable`
   - `SpeechTranscriber.supportedLocale(equivalentTo:)`
   - `SpeechTranscriber.installedLocales` / `supportedLocales` when showing
     language choices.
3. Pick a documented preset:
   - `.transcription` for basic accurate transcription.
   - `.progressiveTranscription` for live UI updates.
   - `.timeIndexedProgressiveTranscription` when playback highlighting needs
     `audioTimeRange`.
4. Install required assets with `AssetInventory.assetInstallationRequest`.
5. Convert live audio buffers to
   `SpeechAnalyzer.bestAvailableAudioFormat(compatibleWith:)` before yielding
   `AnalyzerInput`.
6. Consume module results from their `AsyncSequence` in a separate task.
7. Finish explicitly with `finalizeAndFinish(through:)`,
   `finalizeAndFinishThroughEndOfInput()`, or `cancelAndFinishNow()`.

Do not use an `offlineTranscription` preset; Apple does not document one.
Finishing an `AsyncStream` input sequence does not finish the analyzer session.

## SFSpeechRecognizer Setup

### Creating a recognizer with locale

```swift
import Speech

// Default locale (user's current language)
let recognizer = SFSpeechRecognizer()

// Specific locale
let recognizer = SFSpeechRecognizer(locale: Locale(identifier: "en-US"))

// Check if recognition is available for this locale
guard let recognizer, recognizer.isAvailable else {
    print("Speech recognition not available")
    return
}
```

### Monitoring availability changes

```swift
final class SpeechManager: NSObject, SFSpeechRecognizerDelegate {
    private let recognizer = SFSpeechRecognizer()!

    override init() {
        super.init()
        recognizer.delegate = self
    }

    func speechRecognizer(
        _ speechRecognizer: SFSpeechRecognizer,
        availabilityDidChange available: Bool
    ) {
        // Update UI — disable record button when unavailable
    }
}
```

## Authorization

Request **both** speech recognition and microphone permissions before starting
live transcription. Add these keys to `Info.plist`:

- `NSSpeechRecognitionUsageDescription`
- `NSMicrophoneUsageDescription`

```swift
import Speech
import AVFoundation

func requestPermissions() async -> Bool {
    let speechStatus = await withCheckedContinuation { continuation in
        SFSpeechRecognizer.requestAuthorization { status in
            continuation.resume(returning: status)
        }
    }
    guard speechStatus == .authorized else { return false }

    let micStatus: Bool
    if #available(iOS 17, *) {
        micStatus = await AVAudioApplication.requestRecordPermission()
    } else {
        micStatus = await withCheckedContinuation { continuation in
            AVAudioSession.sharedInstance().requestRecordPermission { granted in
                continuation.resume(returning: granted)
            }
        }
    }
    return micStatus
}
```

## Live Microphone Transcription

The standard pattern: `AVAudioEngine` captures microphone audio → buffers are
appended to `SFSpeechAudioBufferRecognitionRequest` → results stream in.

```swift
import Speech
import AVFoundation

final class LiveTranscriber {
    private let recognizer = SFSpeechRecognizer(locale: Locale(identifier: "en-US"))!
    private let audioEngine = AVAudioEngine()
    private var recognitionRequest: SFSpeechAudioBufferRecognitionRequest?
    private var recognitionTask: SFSpeechRecognitionTask?

    func startTranscribing() throws {
        // Cancel any in-progress task
        recognitionTask?.cancel()
        recognitionTask = nil

        // Configure audio session
        let audioSession = AVAudioSession.sharedInstance()
        try audioSession.setCategory(.record, mode: .measurement, options: .duckOthers)
        try audioSession.setActive(true, options: .notifyOthersOnDeactivation)