AVQueuePlayer playback freezes when removing items from queue

Question

I successfully use AVQueuePlayer to queue and play AVPlayerItems. However, the problems begin when I alter the players queue with calls to removeItem: method. My assumption was that I can freely modify this queue as long as I don't touch the currently played item, but it seems that each call to removeItem: freezes the playback for a moment.

Consider the following code snippet:

+ (void)setBranch:(BranchType)bType {
    NSArray* items = [dynamicMusicPlayer items];
    for (AVPlayerItem* item in [items copy]) {
        if (item == dynamicMusicPlayer.currentItem) {
            continue; // don't remove the currently played item
        }
        [dynamicMusicPlayer removeItem:item];
    }
    [self queueNextBlockFromBranchType:bType];
    currentBranch = bType;
}

You can guess from this, that it's a dynamic music player that plays the music from different branches. So basically, when I comment the line where I remove items, it plays all ok, but obviously the branch is not changed as soon as I want it to. The freeze occurs exactly at the time the removing happens, so the currently played item is being interrupted, but the transition between the actual items is seamless. Also note that I never have more than 2 items in the queue, so in the loop I basically remove one item only.

So, my question is: is there any way to avoid this freeze? And what is causing the freeze on the first place?

Edit So for the people who encountered the same problem, the solution for me was to stop using AVFoundation and use OrigamiEngine instead.

score 0 · Answer 1 · answered May 23 '13 at 20:39

Instead of removing the item in the loop, you could consider scheduling an NSOperation to do it later.

[[NSOperationQueue mainQueue] addOperationWithBlock:^{
    // do something here
}];

Ex:

+ (void)setBranch:(BranchType)bType {
    NSArray* items = [dynamicMusicPlayer items];
    for (AVPlayerItem* item in [items copy]) {
        if (item == dynamicMusicPlayer.currentItem) {
            continue; // don't remove the currently played item
        }
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            [dynamicMusicPlayer removeItem:item];
        }];
    }
    [self queueNextBlockFromBranchType:bType];
    currentBranch = bType;
}

I don't know if this will help, but it'll at least shift the actual item removal to a scheduled operation that the device can decide when to run.

Sorry about that - I was hoping it would schedule it such that it would help. Another option might be to schedule it on a different thread, but I doubt that'll perform any better. — jimbo, May 24 '13 at 19:54

score 0 · Answer 2 · answered May 24 '13 at 19:59

0

This is a much hackier solution, but it might help.

Rather than removing the item from dynamicMusicPlayer immediately, you could mark it for removal by adding it to a separately maintained list of things to remove.

Then, when the AVQueuePlayer is about to advance to the next item, sweep through your list of deletable items and take them out. That way the blip occurs in the boundary between items rather than during playback.

answered May 24 '13 at 19:59

jimbo

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Unfortunately the main reason I decided to use the AVQueuePlayer is to have seamless transitions between tracks and not interrupted playback, so this will only shift the freeze to in between the tracks which is not acceptable. I actually started to develop my own queued player based on AVAudioPlayer as I'm already very disappointed how the AVQueuePlayer interface is very minimalistic (no volume control etc.) – lawicko May 26 '13 at 07:27
Yeah, I hear you. In developing the Brightcove iOS SDK[1], we ran into a ton of trouble with AVQueuePlayer. It has a lot of strange black-box behavior that rendered it unusable for us. In the end, we had to adopt a strategy of creating a new AVPlayer for each item to be played. The details of why/how we did this is outside the scope of this comment box however :) [1] http://support.brightcove.com/en/video-cloud/docs/brightcove-video-cloud-player-sdk-ios – jimbo May 29 '13 at 21:04

AVQueuePlayer playback freezes when removing items from queue

2 Answers2