iOS中使用AVAudioRecorder录制Opus格式音频的配置问题

Hey there, let's break down how to resolve your Opus recording problem and find the best setup for your 30-second social audio posts.

Why Your Current Opus Setup Isn't Working #

Your issues (untriggered delegate methods, -160dB meter readings, missing file URL) stem from two critical misconfigurations:

1. Unsupported Sample Rate: Opus does NOT support 44100Hz. It only works with these sample rates: 8000, 12000, 16000, 24000, or 48000Hz.
2. Invalid Bitrate: Setting AVEncoderBitRateKey to 16 means 16 bits per second—way too low for any usable audio. You need to specify a value in bits per second (e.g., 32000 for 32kbps).

Corrected Opus Recording Configuration #

Here's a fixed version of your setup that will work with AVAudioRecorder:

let fileMgr = FileManager.default
let dirPaths = fileMgr.urls(for: .documentDirectory, in: .userDomainMask)
let soundFileURL = dirPaths[0].appendingPathComponent("audio.opus")

// Correct Opus-compatible settings
let recordSettings: [String: Any] = [
    AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue,
    AVEncoderBitRateKey: 48000, // 48kbps—balances quality and file size
    AVNumberOfChannelsKey: 1, // Mono is ideal for social audio
    AVFormatIDKey: kAudioFormatOpus,
    AVSampleRateKey: 48000.0 // Opus's recommended optimal sample rate
]

// Initialize recorder (don't forget error handling!)
do {
    audioRecorder = try AVAudioRecorder(url: soundFileURL, settings: recordSettings)
    audioRecorder.delegate = self
    audioRecorder.isMeteringEnabled = true
    audioRecorder.prepareToRecord()
    audioRecorder.record()
} catch let error {
    print("Recorder init failed: \(error.localizedDescription)")
}

Fix for Delegate Method #

Also, avoid using your own audioRecorder property in the delegate callback—use the provided recorder parameter instead to prevent nil issues:

func audioRecorderDidFinishRecording(_ recorder: AVAudioRecorder, successfully flag: Bool) {
    print("Recording duration: \(recorder.currentTime)")
    if flag {
        self.audioFileUrl = recorder.url
        print("Recording saved to: \(recorder.url)")
    } else {
        print("Recording failed to finish successfully")
    }
}

Optimal Configuration for 30-Second Social Posts #

For social audio (where fast uploads and good playback quality are key), use these settings:

• Sample Rate: 48000Hz (Opus’s most efficient sample rate for full-range audio)
• Channels: 1 (Mono cuts file size in half without noticeable quality loss for voice/social audio)
• Bitrate: 32–64kbps
  • 32kbps: Great for voice-only content (small file size ~120KB for 30s)
  • 48–64kbps: Ideal for mixed audio (voice + background sounds, ~180–240KB for 30s)
• Quality: AVAudioQuality.high (works well paired with the above bitrates)

Extra Notes #

• Permissions: Ensure you’ve requested microphone access in Info.plist with NSMicrophoneUsageDescription.
• Playback: iOS 11+ supports Opus playback natively via AVPlayer or AVAudioPlayer (no need for third-party libraries).
• Alternative: If you need more control, consider using AVAssetWriter instead of AVAudioRecorder—it’s more flexible for encoding Opus and other formats, but requires more setup.

内容的提问来源于stack exchange，提问作者Zahid Usman Cheema