IOS AudioQueue doesnt play when enqueue packets late

Question

I have an app that enqueues packets to AudioQueue, and it's working perfectly. The problem is when I have a delay in the network, and I can't serve packets in time to AudioQueue.

All the application is working well and the enqueueBuffer doesnt return any error, but AudioQueue is discarding packets (so I have no sound), because they are too old.

Can I force AudioQueue to play those audio packets?, or at least, know that the packets are being discarded?. Because if I know it, i can do Pause-Play to restart the Queue... (not very good solution, but I haven't anything better)

Because the delay could be very big, I can't use a big buffer, because this would minimice error, but not solve it

Thank you very much

Anonymous User Anonymous User · Accepted Answer · 2016-03-29T00:57:40

You're on the right track. You can handle network delays by detecting in your callback procedure when you have reached the end of your network buffer, then pausing the AudioQueue. Later on, restart the queue once enough packets have been buffered. Your code would look like this

if playerState.packetsRead == playerState.packetsWritten {
    playerState.isPlaying = false
    AudioQueuePause(aq)
}

And in your network code

if (playerState.packetsWritten >= playerState.packetsRead + kNumPacketsToBuffer) {
    if !playerState.isPlaying {
        playerState.isPlaying = true

        for buffer in playerState.buffers {
            audioCallback(playerState, aq: playerState.queue, buffer: buffer)
        }

        AudioQueueStart(playerState.queue, nil)
    }
}

You would also need to update your code so that every time you receive a packet from the network, playerState.packetsWritten is incremented, and similarly for playerState.packetsRead when you add a packet to the audio queue. The optimal number for kNumPacketsToBuffer depends on the codec and network conditions. I would recommend using 256 for AAC and adjusting up/down based on performance.

IOS AudioQueue doesnt play when enqueue packets late

1 Answers