Ios 不带AVAsset的纯色合成

这是我的最终目标：我想使用

AVVideoCompositionCoreAnimationTool

从核心动画创建视频我不会在这篇文章中使用现有的AVAsset。

我的问题是，我如何使用

AVMutableComposition

在给定的时间内制作一个静态纯色视频？在我弄清楚之后，我可以添加动画

这是我的密码：

- (void)exportVideo {

AVMutableComposition *mixComposition = [AVMutableComposition composition];
CMTimeRange timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(10, 600));
[mixComposition insertEmptyTimeRange:timeRange];

AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[videoTrack insertEmptyTimeRange:timeRange];
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = timeRange;
mainInstruction.backgroundColor = [UIColor blueColor].CGColor;

AVMutableVideoComposition *mainComposition = [AVMutableVideoComposition videoComposition];

mainComposition.renderSize = CGSizeMake(500, 500);
mainComposition.instructions = [NSArray arrayWithObject:mainInstruction];
mainComposition.frameDuration = CMTimeMake(1, 30);

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"FinalVideo-%d.mov",arc4random() % 1000]];
NSURL *url = [NSURL fileURLWithPath:myPathDocs];

AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
                                                                  presetName:AVAssetExportPresetHighestQuality];
exporter.outputURL = url;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mainComposition;

[exporter exportAsynchronouslyWithCompletionHandler:^{
    dispatch_async(dispatch_get_main_queue(), ^{
        [self exportDidFinish:exporter];
    });
}];

}

我知道您必须至少向mixComposition添加一个曲目，因此我添加了一个视频曲目并插入了一个空的时间范围，但当我调用

exportAsynchronouslyWithCompletionHandler

时，该处理程序从未被调用。我可以在调用export后的任何时间内添加

dispatch\u

，并观察exporter的状态为

AVAssetExportSessionStatusExporting

---

我做错了什么？

在几个月前尝试过这个之后，我发现让它工作起来的唯一可靠方法是在AVMutableCompositionTrack中使用一个简短的空白视频，然后用所需的层覆盖它

大约一个月前，由于模拟器中的一个bug，我上传了一个项目到GitHub。你可以下载空白视频，如果你愿意的话。p>

-(void)exportVideo
{
    CGSize renderingSize = CGSizeMake(640, 360); // The desired size of your video
    float displayDuration = 2.0f; //The duration of the desired video, in seconds

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"FinalVideo-%d.mov",arc4random() % 1000]];
    NSURL *url = [NSURL fileURLWithPath:myPathDocs];

    NSError *error;
    [[NSFileManager defaultManager] removeItemAtURL:url error:&error];

    mutableComposition = [AVMutableComposition composition];
    mutableCompositionVideoTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.renderSize = renderingSize;
    videoComposition.frameDuration = CMTimeMake(1, 30);

    CALayer *parentLayer = [CALayer layer];
    CALayer *videoLayer = [CALayer layer];
    parentLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    videoLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    [parentLayer addSublayer:videoLayer];

    videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"blank_1080p" ofType:@"mp4"];
    NSURL *trackUrl = [NSURL fileURLWithPath:path];
    AVAsset *asset = [AVAsset assetWithURL:trackUrl];
    AVAssetTrack *track = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [mutableCompositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,CMTimeMakeWithSeconds(displayDuration, 600)) ofTrack:track atTime:kCMTimeZero error:nil];

    CALayer *imageLayer = [CALayer layer];
    imageLayer.bounds = parentLayer.frame;
    imageLayer.anchorPoint = CGPointMake(0.5, 0.5);
    imageLayer.position = CGPointMake(CGRectGetMidX(imageLayer.bounds), CGRectGetMidY(imageLayer.bounds));
    imageLayer.backgroundColor = [UIColor blueColor].CGColor;
    imageLayer.contentsGravity = kCAGravityResizeAspectFill;
    [parentLayer addSublayer:imageLayer];

    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(displayDuration, 600));
    videoComposition.instructions = @[instruction];

    exporter = [[AVAssetExportSession alloc] initWithAsset:mutableComposition presetName:AVAssetExportPresetHighestQuality];
    exporter.outputURL = url;
    exporter.videoComposition = videoComposition;
    exporter.outputFileType= AVFileTypeMPEG4;
    exporter.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(displayDuration, 600));
    exporter.shouldOptimizeForNetworkUse = YES;

    [exporter exportAsynchronouslyWithCompletionHandler:^(void){
        dispatch_async(dispatch_get_main_queue(), ^{
            [self exportDidFinish:exporter];
        });
    }];
}

---

谢谢最后我做了完全相同的事情，但是有一个空白的音轨。显然也是这样的。你好！我也面临着同样的问题。你是如何创建空白视频或空白音频的？我正在尝试构建最容易创建的资产，以便拥有一个空白资产，以允许真正可查找的资产持续时间！我已经做了几天了，请原谅我的英语评论。我用AdobeAfter特效制作了一段持续几秒钟的空白视频。你可以从我上面的答案中引用的项目下载文件。但是如果<代码>显示持续时间大于“代码>轨道的持续时间？”@ OLKKSIIN ZYHYPROTER，我上面例子中包含的空白视频只有1秒长，但不管显示持续时间是多长，仍然有效。