问题
I am using a subclass of AVQueuePlayer and when I add new AVPlayerItem with a streaming URL the app freezes for about a second or two. By freezing I mean that it doesn't respond to touches on the UI. Also, if I have a song playing already and then add another one to the queue, AVQueuePlayer automatically starts preloading the song while it is still streaming the first one. This makes the app not respond to touches on the UI for two seconds just like when adding the first song but the song is still playing. So that means AVQueuePlayer is doing something in main thread that is causing the apparent "freeze".
I am using insertItem:afterItem: to add my AVPlayerItem. I tested and made sure that this was the method that was causing the delay. Maybe it could be something that AVPlayerItem does when it gets activated by AVQueuePlayer at the moment of adding it to the queue.
Must point out that I am using the Dropbox API v1 beta to get the streaming URL by using this method call:
[[self restClient] loadStreamableURLForFile:metadata.path];
Then when I receive the stream URL I send it to AVQueuePlayer as follows:
[self.player insertItem:[AVPlayerItem playerItemWithURL:url] afterItem:nil];
So my question is: How do I avoid this?
Should I do the preloading of an audio stream on my own without the help of AVPlayer? If so, how do I do this?
Thanks.
回答1:
Don't use playerItemWithURL it's sync.
When you receive the response with the url try this:
AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:nil];
NSArray *keys = @[@"playable"];
[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^() {
[self.player insertItem:[AVPlayerItem playerItemWithAsset:asset] afterItem:nil];
}];
回答2:
Bump, since this is a highly rated question and similar questions online either has outdated answers or aren't great. The whole idea is pretty straight forward with AVKit and AVFoundation, which means no more depending on third party libraries. The only issue is that it took some tinkering around and put the pieces together.
AVFoundation's Player() initialization with url is apparently not thread safe, or rather it's not meant to be. Which means, no matter how you initialize it in a background thread the player attributes are going to be loaded in the main queue causing freezes in the UI especially in UITableViews and UICollectionViews. To solve this issue Apple provided AVAsset which takes a URL and assists in loading the media attributes like track, playback, duration etc. and can do so asynchronously, with a best part being that this loading process is cancellable (unlike other Dispatch queue background threads where ending a task may not be that straight forward). This means, there is no need to worry about lingering zombie threads in the background as you scroll fast on a table view or collection view, ultimately piling up on the memory with a whole bunch of unused objects. This cancellable feature is great, and allows us to cancel any lingering AVAsset async load if it is in progress but only during cell dequeue. The async loading process can be invoked by the loadValuesAsynchronously method, and can be cancelled (at will) at any later time (if still in progress).
Don't forget to exception handle properly using the results of loadValuesAsynchronously. In Swift (3/4), here's how you would would load a video asynchronously and handle situations if the async process fails (due to slow networks, etc.)-
TL;DR
TO PLAY A VIDEO
let asset = AVAsset(url: URL(string: self.YOUR_URL_STRING))
let keys: [String] = ["playable"]
var player: AVPlayer!
asset.loadValuesAsynchronously(forKeys: keys, completionHandler: {
var error: NSError? = nil
let status = asset.statusOfValue(forKey: "playable", error: &error)
switch status {
case .loaded:
DispatchQueue.main.async {
let item = AVPlayerItem(asset: asset)
self.player = AVPlayer(playerItem: item)
let playerLayer = AVPlayerLayer(player: self.player)
playerLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill
playerLayer.frame = self.YOUR_VIDEOS_UIVIEW.bounds
self.YOUR_VIDEOS_UIVIEW.layer.addSublayer(playerLayer)
self.player.isMuted = true
self.player.play()
}
break
case .failed:
DispatchQueue.main.async {
//do something, show alert, put a placeholder image etc.
}
break
case .cancelled:
DispatchQueue.main.async {
//do something, show alert, put a placeholder image etc.
}
break
default:
break
}
})
NOTE:
Based on what your app wants to achieve you may still have to do some amount of tinkering to tune it to get smoother scroll in a UITableView or UICollectionView. You may also need to implement some amount of KVO on the AVPlayerItem properties for it to work and there's plenty of posts here in SO that discuss AVPlayerItem KVOs in detail.
TO LOOP THROUGH ASSETS (video loops/GIFs)
To loop a video, you can use the same method above and introducing AVPlayerLooper. Here's a sample code to loop a video (or perhaps a short video in GIF style). Note the use of duration key which is required for our video loop.
let asset = AVAsset(url: URL(string: self.YOUR_URL_STRING))
let keys: [String] = ["playable","duration"]
var player: AVPlayer!
var playerLooper: AVPlayerLooper!
asset.loadValuesAsynchronously(forKeys: keys, completionHandler: {
var error: NSError? = nil
let status = asset.statusOfValue(forKey: "duration", error: &error)
switch status {
case .loaded:
DispatchQueue.main.async {
let playerItem = AVPlayerItem(asset: asset)
self.player = AVQueuePlayer()
let playerLayer = AVPlayerLayer(player: self.player)
//define Timerange for the loop using asset.duration
let duration = playerItem.asset.duration
let start = CMTime(seconds: duration.seconds * 0, preferredTimescale: duration.timescale)
let end = CMTime(seconds: duration.seconds * 1, preferredTimescale: duration.timescale)
let timeRange = CMTimeRange(start: start, end: end)
self.playerLooper = AVPlayerLooper(player: self.player as! AVQueuePlayer, templateItem: playerItem, timeRange: timeRange)
playerLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill
playerLayer.frame = self.YOUR_VIDEOS_UIVIEW.bounds
self.YOUR_VIDEOS_UIVIEW.layer.addSublayer(playerLayer)
self.player.isMuted = true
self.player.play()
}
break
case .failed:
DispatchQueue.main.async {
//do something, show alert, put a placeholder image etc.
}
break
case .cancelled:
DispatchQueue.main.async {
//do something, show alert, put a placeholder image etc.
}
break
default:
break
}
})
EDIT : As per the documentation, AVPlayerLooper requires the duration property of the asset to be fully loaded in order to be able to loop through videos. Also, the timeRange: timeRange with the start and end timerange in the AVPlayerLooper initialization is really optional if you want an infinite loop. I have also realized since I posted this answer that AVPlayerLooper is only about 70-80% accurate in looping videos, especially if your AVAsset needs to stream the video from a URL. In order to solve this issue there is a totally different (yet simple) approach to loop a video-
//this will loop the video since this is a Gif
let interval = CMTime(value: 1, timescale: 2)
self.timeObserverToken = self.player?.addPeriodicTimeObserver(forInterval: interval, queue: DispatchQueue.main, using: { (progressTime) in
if let totalDuration = self.player?.currentItem?.duration{
if progressTime == totalDuration{
self.player?.seek(to: kCMTimeZero)
self.player?.play()
}
}
})
回答3:
Gigisommo's answer for Swift 3 including the feedback from the comments:
let asset = AVAsset(url: url)
let keys: [String] = ["playable"]
asset.loadValuesAsynchronously(forKeys: keys) {
DispatchQueue.main.async {
let item = AVPlayerItem(asset: asset)
self.playerCtrl.player = AVPlayer(playerItem: item)
}
}
来源：https://stackoverflow.com/questions/7701212/avplayer-freezes-the-app-at-the-start-of-buffering-an-audio-stream