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我正在使用 AVPlayer 通过 url 播放远程音频和视频文件。使用我目前的实现，在 iOS8.4 及更高版本上一切都很好，唯一的问题是在 iOS8.3 上出现视频但音频在后台运行。

我创建一个AVURLAsset这样的：

AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:soundURL options:nil];
NSArray *keys = @[@"playable", @"duration"];
avAsset = asset;
[avAsset loadValuesAsynchronouslyForKeys:keys completionHandler:^() {
    NSError *error = nil;
    AVKeyValueStatus playableStatus = [asset statusOfValueForKey:@"playable" error:&error];
    AVKeyValueStatus durationStatus = [asset statusOfValueForKey:@"duration" error:&error];
    switch (playableStatus) {
        case AVKeyValueStatusLoaded:{
            AVPlayerItem *item = [AVPlayerItem playerItemWithAsset:avAsset];

            if (!mediaPlayer) {
                mediaPlayer = [[AVPlayer alloc] initWithPlayerItem:item];
                mediaPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;
                [item addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:nil];
                [item addObserver:self forKeyPath:@"rate" options:NSKeyValueObservingOptionNew context:nil];
                [[NSNotificationCenter defaultCenter] addObserver:self
                                                         selector:@selector(playerItemDidReachEnd:)
                                                             name:AVPlayerItemDidPlayToEndTimeNotification
                                                           object:[mediaPlayer currentItem]];
            } else {
                if (isNewURL) {
                    [mediaPlayer replaceCurrentItemWithPlayerItem:item];
                }
            }

            [mediaPlayer seekToTime:kCMTimeZero];
            break;
        }
        case AVKeyValueStatusLoading:
            [SBNotificationMessenger notifyMessage:@"Buffering..."];
            break;
        case AVKeyValueStatusFailed:
            [SBNotificationMessenger notifyError:error.localizedDescription];
            break;
        default:
            break;
    }

    if (durationStatus == AVKeyValueStatusLoaded) {
        dispatch_async(dispatch_get_main_queue(), ^{
            startedPlaying(YES);
        });
    }
}];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (object == mediaPlayer.currentItem) {
        if ([keyPath isEqualToString:@"status"]) {
            [self handleMediaPlayerStatus];
        } else if ([keyPath isEqualToString:@"rate"]) {
            [self handleMediaPlayerRateStatus];
        }
    }
}

- (void)handleMediaPlayerStatus
{
    if (mediaPlayer.status == AVPlayerStatusFailed) {
        DDLogError(@"Media player status: failed!");
    } else if (mediaPlayer.status == AVPlayerStatusReadyToPlay) {
        DDLogInfo(@"Media player status: ready!");
        [mediaPlayer play];
    } else if (mediaPlayer.status == AVPlayerItemStatusUnknown) {
        DDLogInfo(@"Media player status: unknown");
    }
}
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