Implementing flexible enhanced buffering for your content

Overview

If you’re working with content that requires flexibility with buffering, use the AVSampleBufferAudioRenderer and AVSampleBufferRenderSynchronizer classes.

To implement flexible enhanced buffering, complete the following steps.

1. Create a serialization queue to perform all playback operations on, and create the audio renderer and the render synchronizer to establish the media timeline.

let serializationQueue = DispatchQueue(label: "sample.buffer.player.serialization.queue")
let audioRenderer = AVSampleBufferAudioRenderer()
let renderSynchronizer = AVSampleBufferRenderSynchronizer()

1. Observe when the renderer has flushed enqueued audio, such as when the rate of playback increases or decreases, and re-enqueue audio data starting from the time the flush occurred.

automaticFlushObserver = NotificationCenter.default.addObserver(forName: .AVSampleBufferAudioRendererWasFlushedAutomatically,
                                                                object: audioRenderer,
                                                                queue: nil) { [weak self] notification in
    self?.serializationQueue.async { [weak self] in
        guard let self = self else { return } 
        // Restart from the point where the flush interrupts the audio.
        let restartTime = (notification.userInfo?[AVSampleBufferAudioRendererFlushTimeKey] as? NSValue)?.timeValue
        self.autoflushPlayback(restartingAt: restartTime)
    }
}

1. Add the audio renderer to the render synchronizer, to tell the audio renderer to follow the media timeline.

renderSynchronizer.addRenderer(audioRenderer)

1. Tell the audio renderer to start processing audio data, and set the render synchronizer’s rate to 1 to start playback.

serializationQueue.async { [weak self] in
    guard let self = self else { return }
    // Start processing audio data and stop when there's no more data.
    self.audioRenderer.requestMediaDataWhenReady(on: serializationQueue) { [weak self] in
        guard let self = self else { return }
        while self.audioRenderer.isReadyForMoreMediaData {
            let sampleBuffer = self.nextSampleBuffer() // Returns nil at end of data.
            if let sampleBuffer = sampleBuffer {
                self.audioRenderer.enqueue(sampleBuffer)
            } else {
                // Tell the renderer to stop requesting audio data.
                audioRenderer.stopRequestingMediaData()
            }
        }
    }

    // Start playback at the natural rate of the media.
    self.renderSynchronizer.rate = 1.0
}

See Also

Buffered playback

• Implementing simple enhanced buffering for your content
• Integrating AirPlay for long-form video apps