如何使用AVFoundation组合具有不同方向的视频剪辑

Question

我正在尝试使用AVFoundation将多个视频剪辑组合成一个.我可以使用下面的代码使用AVMutableComposition创建单个视频

AVMutableComposition *composition = [AVMutableComposition composition];

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

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

CMTime startTime = kCMTimeZero;

/*videoClipPaths is a array of paths of the video clips recorded*/

//for loop to combine clips into a single video
for (NSInteger i=0; i < [videoClipPaths count]; i++) {

    NSString *path = (NSString*)[videoClipPaths objectAtIndex:i];

    NSURL *url = [[NSURL alloc] initFileURLWithPath:path];

    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:url options:nil];
    [url release];

    AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    AVAssetTrack *audioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    //set the orientation
    if(i == 0)
    {
        [compositionVideoTrack setPreferredTransform:videoTrack.preferredTransform];
    }

    ok = [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:videoTrack atTime:startTime error:nil];
    ok = [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:audioTrack atTime:startTime error:nil];

    startTime = CMTimeAdd(startTime, [asset duration]);
}

//export the combined video
NSString *combinedPath = /* path of the combined video*/;

NSURL *url = [[NSURL alloc] initFileURLWithPath: combinedPath];

AVAssetExportSession *exporter = [[[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPreset640x480] autorelease];

exporter.outputURL = url;
[url release];

exporter.outputFileType = [[exporter supportedFileTypes] objectAtIndex:0];

[exporter exportAsynchronouslyWithCompletionHandler:^(void){[self combineVideoFinished:exporter.outputURL status:exporter.status error:exporter.error];}];

如果所有视频剪辑都以相同方向(纵向或横向)录制,则上述代码可以正常工作.但是,如果我在剪辑中混合了方向,则最终视频的一部分会向右(或左)旋转90度.

我想知道有没有办法在编写时将所有剪辑转换为相同的方向(例如第一个剪辑的方向).从我从XCode文档中读取的内容AVMutableVideoCompositionLayerInstruction似乎可用于转换AVAsset,但我不确定如何创建并将几个不同的层指令应用于相应的剪辑并在合成中使用然后(AVMutableComposition*)

任何帮助,将不胜感激!

Answer 1

这就是我的工作.然后我使用AVAssetExportSession来创建实际文件.但是我警告你,CGAffineTransforms有时应用较晚,所以在视频转换之前你会看到一两个原版.我不知道为什么会发生这种情况,不同的视频组合会产生预期的结果,但有时它会关闭.

AVMutableComposition *composition = [AVMutableComposition composition];    
AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition]; 
videoComposition.frameDuration = CMTimeMake(1,30); 
videoComposition.renderScale = 1.0;

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

// Get only paths the user selected NSMutableArray *array = [NSMutableArray array]; for(NSString* string in videoPathArray){
if(![string isEqualToString:@""]){
    [array addObject:string];
} 

self.videoPathArray = array;

float time = 0;

for (int i = 0; i<self.videoPathArray.count; i++) {

    AVURLAsset *sourceAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:[videoPathArray objectAtIndex:i]] options:[NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey]];

    NSError *error = nil;

    BOOL ok = NO;
    AVAssetTrack *sourceVideoTrack = [[sourceAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

    CGSize temp = CGSizeApplyAffineTransform(sourceVideoTrack.naturalSize, sourceVideoTrack.preferredTransform);
    CGSize size = CGSizeMake(fabsf(temp.width), fabsf(temp.height));
    CGAffineTransform transform = sourceVideoTrack.preferredTransform;

    videoComposition.renderSize = sourceVideoTrack.naturalSize;
    if (size.width > size.height) {
        [layerInstruction setTransform:transform atTime:CMTimeMakeWithSeconds(time, 30)];
    } else {

        float s = size.width/size.height;

        CGAffineTransform new = CGAffineTransformConcat(transform, CGAffineTransformMakeScale(s,s));

        float x = (size.height - size.width*s)/2;

        CGAffineTransform newer = CGAffineTransformConcat(new, CGAffineTransformMakeTranslation(x, 0));

        [layerInstruction setTransform:newer atTime:CMTimeMakeWithSeconds(time, 30)];
    }

    ok = [compositionVideoTrack insertTimeRange:sourceVideoTrack.timeRange ofTrack:sourceVideoTrack atTime:[composition duration] error:&error];

    if (!ok) {
        // Deal with the error.
        NSLog(@"something went wrong");
    }

    NSLog(@"\n source asset duration is %f \n source vid track timerange is %f %f \n composition duration is %f \n composition vid track time range is %f %f",CMTimeGetSeconds([sourceAsset duration]), CMTimeGetSeconds(sourceVideoTrack.timeRange.start),CMTimeGetSeconds(sourceVideoTrack.timeRange.duration),CMTimeGetSeconds([composition duration]), CMTimeGetSeconds(compositionVideoTrack.timeRange.start),CMTimeGetSeconds(compositionVideoTrack.timeRange.duration));

    time += CMTimeGetSeconds(sourceVideoTrack.timeRange.duration);
}

instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
instruction.timeRange = compositionVideoTrack.timeRange; 
videoComposition.instructions = [NSArray arrayWithObject:instruction];

这就是我的工作.然后我使用AVAssetExportSession来创建实际文件.但是我警告你,CGAffineTransforms有时应用较晚,所以在视频转换之前你会看到一两个原版.我不知道为什么会发生这种情况,不同的视频组合会产生预期的结果,但有时它会关闭.