ios - 从单元测试运行时，CATextLayer不会出现在AVMutableComposition中

编辑:最奇怪的事情是:从完整的应用程序运行此代码似乎一切正常，但是我一直在通过单元测试运行电影的创建，但仅在那儿不起作用。试图弄清楚为什么会这样...

我正在尝试使用AVMutableComposition组合视频+音频+文本，并将其导出到新视频。

我的代码基于WWDC '10的AVEditDemo

我在CATextLayer中添加了紫色背景，因此我可以知道它已导出到电影中，但是没有显示任何文本...我尝试使用各种字体，位置，颜色定义，但没有任何帮助，因此我决定在此处发布代码，看看是否有人偶然发现类似内容并可以告诉我我所缺少的内容。

这是代码(self.audio和self.video是AVURLAssets):

CMTime exportDuration = self.audio.duration;

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

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *videoTrack = [[self.video tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

// add the video in loop until the audio ends
CMTime currStartTime = kCMTimeZero;
while (CMTimeCompare(currStartTime, exportDuration) < 0) {
    CMTime timeRemaining = CMTimeSubtract(exportDuration, currStartTime);
    CMTime currLoopDuration = self.video.duration;

    if (CMTimeCompare(currLoopDuration, timeRemaining) > 0) {
        currLoopDuration = timeRemaining;
    }
    CMTimeRange currLoopTimeRange = CMTimeRangeMake(kCMTimeZero, currLoopDuration);

    [compositionVideoTrack insertTimeRange:currLoopTimeRange ofTrack:videoTrack
                                    atTime:currStartTime error:nil];

    currStartTime = CMTimeAdd(currStartTime, currLoopDuration);
}

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

AVAssetTrack *audioTrack = [self.audio.tracks objectAtIndex:0];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.audio.duration) ofTrack:audioTrack atTime:kCMTimeZero error:nil];

AVMutableVideoComposition *videoComposition;

// the text layer part - THIS IS THE PART THAT DOESN'T WORK WELL
CALayer *animatedTitleLayer = [CALayer layer];
CATextLayer *titleLayer = [[CATextLayer alloc] init];
titleLayer.string = @"asdfasdf";
titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0, 0, self.video.naturalSize.width / 2, self.video.naturalSize.height / 2);
titleLayer.opacity = 1.0;
titleLayer.backgroundColor = [UIColor purpleColor].CGColor;

[animatedTitleLayer addSublayer:titleLayer];
animatedTitleLayer.position = CGPointMake(self.video.naturalSize.width / 2.0, self.video.naturalSize.height / 2.0);

// build a Core Animation tree that contains both the animated title and the video.
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, self.video.naturalSize.width, self.video.naturalSize.height);
videoLayer.frame = CGRectMake(0, 0, self.video.naturalSize.width, self.video.naturalSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:animatedTitleLayer];

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

AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
passThroughInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, exportDuration);
AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

passThroughInstruction.layerInstructions = [NSArray arrayWithObject:passThroughLayer];
videoComposition.instructions = [NSArray arrayWithObject:passThroughInstruction];

videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.renderSize = self.video.naturalSize;

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetMediumQuality];

exportSession.videoComposition = videoComposition;
exportSession.outputURL = [NSURL fileURLWithPath:self.outputFilePath];
exportSession.outputFileType = AVFileTypeQuickTimeMovie;

[exportSession exportAsynchronouslyWithCompletionHandler:^() {
    // save the video ...
}];

最佳答案

我在不同的背景下遇到了同样的问题。就我而言，我已经将AVMutableComposition的准备移到了后台线程。将准备工作的这一部分移回主队列/线程，可使CATextLayer叠加层再次正常工作。

这可能并不完全适用于您的单元测试上下文，但我的猜测是CATextLayer/AVFoundation依赖于该线程上下文中正在运行/可用的UIKit/AppKit的某些部分(图形上下文？当前屏幕？)，这可能解释我们俩都看到的失败。

关于ios - 从单元测试运行时，CATextLayer不会出现在AVMutableComposition中，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/10281872/