iPhone SDK。是否可以使用 AVURLlAsset/AVMutableComposition 在 AVplayer 中旋转视频？

Question

我有一个使用 AVPlayer 的简单视频编辑 View 。我使用一个或多个 AVURLAsset 创建一个 AVMutableComposition。一切正常，但视频总是旋转 90 度。即，如果源视频是以纵向模式拍摄的。 AVPlayer 以横向模式显示它，反之亦然。我已经浏览了文档并“谷歌”了它，但找不到解决方案。也许我找错了地方。

有人可以帮忙吗？

提前致谢；

让-皮埃尔

Answer 1

据我了解，您遇到了一些方向问题，例如纵向视频处于横向模式，有时视频会上下颠倒。这是由于默认的 AVAsset 方向造成的。使用默认 iPhone 相机应用程序录制的所有影片和图像文件都将视频帧设置为横向，因此媒体以横向模式保存。AVAsset 有一个 PreferredTransform 属性，其中包含媒体方向信息，每当您使用“照片”应用程序或 QuickTime 查看媒体文件时，该属性都会应用于媒体文件。您可以通过对 AVAsset 对象应用必要的转换来轻松纠正此问题。但由于您的两个视频文件可以具有不同的方向，因此您需要使用两个单独的 AVMutableCompositionTrack 实例，而不是像最初那样使用一个(假设)实例。创建两个 AVMutableCompositionTrack 视频轨道由于您现在有两个单独的 AVMutableCompositionTrack 实例，因此您需要将 AVMutableVideoCompositionLayerInstruction 应用于每个轨道以固定方向。所以添加以下代码

    //  Create AVMutableVideoCompositionInstruction
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeAdd(firstAsset.duration, secondAsset.duration));
// Create an AVMutableVideoCompositionLayerInstruction for the first track
AVMutableVideoCompositionLayerInstruction *firstlayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:firstTrack];
AVAssetTrack *firstAssetTrack = [[firstAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
UIImageOrientation firstAssetOrientation_  = UIImageOrientationUp;
BOOL isFirstAssetPortrait_  = NO;
CGAffineTransform firstTransform = firstAssetTrack.preferredTransform;
if (firstTransform.a == 0 && firstTransform.b == 1.0 && firstTransform.c == -1.0 && firstTransform.d == 0) {
    firstAssetOrientation_ = UIImageOrientationRight; 
    isFirstAssetPortrait_ = YES;
}
if (firstTransform.a == 0 && firstTransform.b == -1.0 && firstTransform.c == 1.0 && firstTransform.d == 0) {
    firstAssetOrientation_ =  UIImageOrientationLeft; 
    isFirstAssetPortrait_ = YES;
}
if (firstTransform.a == 1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == 1.0) {
    firstAssetOrientation_ =  UIImageOrientationUp;
}
if (firstTransform.a == -1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == -1.0) {
    firstAssetOrientation_ = UIImageOrientationDown;
}
[firstlayerInstruction setTransform:firstAsset.preferredTransform atTime:kCMTimeZero];
[firstlayerInstruction setOpacity:0.0 atTime:firstAsset.duration];
//  Create an AVMutableVideoCompositionLayerInstruction for the second track
AVMutableVideoCompositionLayerInstruction *secondlayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:secondTrack];
AVAssetTrack *secondAssetTrack = [[secondAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
UIImageOrientation secondAssetOrientation_  = UIImageOrientationUp;
BOOL isSecondAssetPortrait_  = NO;
CGAffineTransform secondTransform = secondAssetTrack.preferredTransform;
if (secondTransform.a == 0 && secondTransform.b == 1.0 && secondTransform.c == -1.0 && secondTransform.d == 0) {
    secondAssetOrientation_= UIImageOrientationRight; 
    isSecondAssetPortrait_ = YES;
}
if (secondTransform.a == 0 && secondTransform.b == -1.0 && secondTransform.c == 1.0 && secondTransform.d == 0) {
    secondAssetOrientation_ =  UIImageOrientationLeft; 
    isSecondAssetPortrait_ = YES;
}
if (secondTransform.a == 1.0 && secondTransform.b == 0 && secondTransform.c == 0 && secondTransform.d == 1.0) {
    secondAssetOrientation_ =  UIImageOrientationUp;
}
if (secondTransform.a == -1.0 && secondTransform.b == 0 && secondTransform.c == 0 && secondTransform.d == -1.0) {
    secondAssetOrientation_ = UIImageOrientationDown;
}
[secondlayerInstruction setTransform:secondAsset.preferredTransform atTime:firstAsset.duration];
}

最后添加说明，这只是应用于第二个轨道的方向修复。

    mainInstruction.layerInstructions = [NSArray arrayWithObjects:firstlayerInstruction, secondlayerInstruction,nil];
AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
mainCompositionInst.frameDuration = CMTimeMake(1, 30);

CGSize naturalSizeFirst, naturalSizeSecond;
if(isFirstAssetPortrait_){
    naturalSizeFirst = CGSizeMake(FirstAssetTrack.naturalSize.height, FirstAssetTrack.naturalSize.width);
} else {
    naturalSizeFirst = FirstAssetTrack.naturalSize;
}
if(isSecondAssetPortrait_){
    naturalSizeSecond = CGSizeMake(SecondAssetTrack.naturalSize.height, SecondAssetTrack.naturalSize.width);
} else {
    naturalSizeSecond = SecondAssetTrack.naturalSize;
}

float renderWidth, renderHeight;
if(naturalSizeFirst.width > naturalSizeSecond.width) {
    renderWidth = naturalSizeFirst.width;
} else {
    renderWidth = naturalSizeSecond.width;
}
if(naturalSizeFirst.height > naturalSizeSecond.height) {
    renderHeight = naturalSizeFirst.height;
} else {
    renderHeight = naturalSizeSecond.height;
}
MainCompositionInst.renderSize = CGSizeMake(renderWidth, renderHeight);

希望这有帮助