AVVideoComposition故障

Question

就像我的一样。来使用它。

我将几个不同的视频剪辑串成一个AVMutableComposition，并试图纠正它们的方向，如果需要的话。

下面是我的代码：

composition = [[AVMutableComposition alloc] init];
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

CMTime nextClipStartTime = kCMTimeZero;

// orientation compensation vars
AVMutableVideoCompositionInstruction *inst = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
NSMutableArray *compInst = [[NSMutableArray alloc] init];

// get view size
CGSize viewSize = playerView.frame.size;

// generate movie assets
for (NSString* moviePath in [currentBlam valueForKey:@"movies"]) {
    NSURL *movieURL = [NSURL fileURLWithPath:moviePath];
    AVURLAsset *movieAsset = [AVURLAsset URLAssetWithURL:movieURL options:nil];  

    // scale asset to fit screen

    CMTimeRange tr = CMTimeRangeFromTimeToTime(CMTimeMakeWithSeconds(0.0f, 1), CMTimeMakeWithSeconds(0.0f, 1));

    //    create video track
    AVAssetTrack *clipVideoTrack = [[movieAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    //    create audio track
    AVAssetTrack *clipAudioTrack = [[movieAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    tr = CMTimeRangeFromTimeToTime(CMTimeMakeWithSeconds(0.0f, 1), CMTimeMakeWithSeconds(CMTimeGetSeconds([movieAsset duration]), 1));

    AVMutableVideoCompositionLayerInstruction *layerInst;
    layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];

    int or = [self orientationForTrack:movieAsset];
    if (or==1) { 
        float rot = (0.0f);
        [layerInst setTransform:CGAffineTransformMakeRotation(rot) atTime:nextClipStartTime];
    } else if (or==2) { 
        float rot = (M_PI);
        [layerInst setTransform:CGAffineTransformMakeRotation(rot) atTime:nextClipStartTime];
    } else if (or==3) { 
        float rot = (M_PI*-0.5f);
        [layerInst setTransform:CGAffineTransformMakeRotation(rot) atTime:nextClipStartTime];
    } else if (or==4) { 
        float rot = (M_PI*0.5f);
        [layerInst setTransform:CGAffineTransformMakeRotation(rot) atTime:nextClipStartTime];
    }

    [layerInst setTransform:clipVideoTrack.preferredTransform atTime:nextClipStartTime];
    [compInst addObject:layerInst];

    //    insert video track
    [compositionVideoTrack insertTimeRange:tr 
                                   ofTrack:clipVideoTrack 
                                    atTime:nextClipStartTime 
                                     error:nil];
    //    insert audio track
    [compositionAudioTrack insertTimeRange:tr 
                                   ofTrack:clipAudioTrack 
                                    atTime:nextClipStartTime 
                                     error:nil];

    nextClipStartTime = CMTimeAdd(nextClipStartTime, tr.duration);
}

//set size and duration
composition.naturalSize = viewSize;
videoComposition.frameDuration = composition.duration;
videoComposition.renderSize = viewSize;
videoComposition.renderScale = 1.0f;

//apply instructions
inst.timeRange = CMTimeRangeMake(kCMTimeZero, composition.duration);
inst.layerInstructions = compInst;
videoComposition.instructions = [NSArray arrayWithObject:inst];

playerItem = [[AVPlayerItem alloc] initWithAsset:composition];
playerItem.videoComposition = videoComposition;
[playerItem addObserver:self forKeyPath:@"status" options:0 context:&ItemStatusContext];
[[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(playerItemDidReachEnd:) 
                                             name:AVPlayerItemDidPlayToEndTimeNotification 
                                           object:playerItem];
player = [AVPlayer playerWithPlayerItem:playerItem];

[playerView setPlayer:player];

当我运行它并填充内容时，没有显示任何内容。

这是以前的工作，没有AVVideoComposition被应用到播放器。事实上，注释掉playerItem.videoComposition = videoComposition允许它工作，尽管不会更正资产轮换。

在这一点上，我知道我只是误解了一些东西。有人能指出是什么吗？

Answer 1

你有没有想过，也许视频旋转的点不是中心，视频正在被拉出屏幕？这可能是完全错误的，但这只是我的第一个想法。

Answer 2

我认为您正在将每个单帧设置为整个剪辑的长度：

videoComposition.frameDuration = composition.duration；