HTTP实时流AVAsset

Question

我正在使用avplayer用OSX实现n个HTTP直播播放器。我能够正确地流它，寻找和获得持续时间，时间等。现在我想采取屏幕截图和处理从它使用OpenCV的帧。我选择使用AVASSetImageGenerator。但是，与AVAsset没有音频和视频轨道，这是与player.currentItem相关的。

轨道出现在player.currentItem.tracks上。所以我不能起诉AVAssetGenerator。在这样的场景中，有谁能帮助找出一个方案来提取屏幕截图和单个帧呢？

请找到下面的代码，我是如何启动HTTP实时流的

提前谢谢。

NSURL* url = [NSURL URLWithString:@"http://devimages.apple.com/iphone/samples/bipbop/bipbopall.m3u8"];
playeritem = [AVPlayerItem playerItemWithURL:url];

[playeritem addObserver:self forKeyPath:@"status" options:0 context:AVSPPlayerStatusContext];
[self setPlayer:[AVPlayer playerWithPlayerItem:playeritem]];
[self addObserver:self forKeyPath:@"player.rate" options:NSKeyValueObservingOptionNew context:AVSPPlayerRateContext];
[self addObserver:self forKeyPath:@"player.currentItem.status" options:NSKeyValueObservingOptionNew context:AVSPPlayerItemStatusContext];
AVPlayerLayer *newPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:[self player]];
[newPlayerLayer setFrame:[[[self playerView] layer] bounds]];
[newPlayerLayer setAutoresizingMask:kCALayerWidthSizable | kCALayerHeightSizable];
[newPlayerLayer setHidden:YES];
[[[self playerView] layer] addSublayer:newPlayerLayer];
[self setPlayerLayer:newPlayerLayer];
[self addObserver:self forKeyPath:@"playerLayer.readyForDisplay" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew context:AVSPPlayerLayerReadyForDisplay];
[self.player play];    

下面是我如何检查视频轨道是否存在资产

case AVPlayerItemStatusReadyToPlay:

                [self setTimeObserverToken:[[self player] addPeriodicTimeObserverForInterval:CMTimeMake(1, 10) queue:dispatch_get_main_queue() usingBlock:^(CMTime time) {
                    [[self timeSlider] setDoubleValue:CMTimeGetSeconds(time)];
                    NSLog(@"%f,%f,%f",[self currentTime],[self duration],[[self player] rate]);
                    AVPlayerItem *item = playeritem;
                    if(item.status == AVPlayerItemStatusReadyToPlay)
                    {
                    AVAsset *asset = (AVAsset *)item.asset;
                    long audiotracks = [[asset tracks] count];
                    long videotracks = [[asset availableMediaCharacteristicsWithMediaSelectionOptions]count];

                    NSLog(@"Track info Audio = %ld,Video=%ld",audiotracks,videotracks);
                    }
                }]];



                AVPlayerItem *item = self.player.currentItem;
                if(item.status != AVPlayerItemStatusReadyToPlay)
                    return;
                AVURLAsset *asset = (AVURLAsset *)item.asset;
                long audiotracks = [[asset tracksWithMediaType:AVMediaTypeAudio]count];
                long videotracks = [[asset tracksWithMediaType:AVMediaTypeVideo]count];

                NSLog(@"Track info Audio = %ld,Video=%ld",audiotracks,videotracks);

Answer 1

这是一个较老的问题，但如果有人需要帮助，我有答案

AVURLAsset *asset = /* Your Asset here! */;
AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
generator.requestedTimeToleranceAfter =  kCMTimeZero;
generator.requestedTimeToleranceBefore =  kCMTimeZero;
for (Float64 i = 0; i < CMTimeGetSeconds(asset.duration) *  /* Put the FPS of the source video here */ ; i++){
    @autoreleasepool {
        CMTime time = CMTimeMake(i, /* Put the FPS of the source video here */);

        NSError *err;
        CMTime actualTime;
        CGImageRef image = [generator copyCGImageAtTime:time actualTime:&actualTime error:&err];

        // Do what you want with the image, for example save it as UIImage
        UIImage *generatedImage = [[UIImage alloc] initWithCGImage:image];

        CGImageRelease(image);
    }
}

通过使用以下代码，可以轻松获得视频的FPS：

float fps=0.00;
if (asset) {
    AVAssetTrack * videoATrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];
    if(videoATrack)
    {
        fps = [videoATrack nominalFrameRate];
    }
}

希望这能帮助那些询问如何从视频中获取所有帧的人，或者只是一些特定的(比如CMTime )帧。请记住，将所有帧保存到一个数组中几乎不会影响内存！