如何使用AVFoundation组合具有不同方向的视频剪辑 [英] How to combine video clips with different orientation using AVFoundation

问题描述

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AVMutableComposition使用下面的代码创建单个视频

I am trying to combine several video clips into one using AVFoundation. I can create a single video using AVMutableComposition using the code below

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，最后的视频会将其中的一部分向右（或左）旋转90度。

The code above works fine if all the video clips were recorded in the same orientation (portrait or landscape). However if I have a mixture of orientations in the clips, the final video will have part of it rotated 90 degrees to the right (or left).

我想知道的是有一种方法可以在组合它们时将所有剪辑转换为相同的方向（例如第一个剪辑的方向）。从我在XCode的文档阅读 AVMutableVideoCompositionLayerInstruction 似乎可以用来转化 AVAsset ，但我不知道如何创建几个不同的图层指令并将其应用于相应的剪辑，然后在合成中使用（ AVMutableComposition * ）

I was wondering is there a way to transform all clips to the same orientation (e.g. the orientation of the first clip) while composing them. From what I read from the XCode document AVMutableVideoCompositionLayerInstruction seems can be used to transform AVAsset, but I am not sure how to create and apply several different layer instruction to corresponding clips and use then in the composition (AVMutableComposition*)

任何帮助我将不胜感激！

Any help would be appreciated!

推荐答案

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有时应用得很晚，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，但有时会关闭。

This is what I do. I then use an AVAssetExportSession to create the actual file. but I warn you, the CGAffineTransforms are sometimes applied late, so you'll see a or two of the original before the video transforms. I have no clue why this happens, a different combination of videos will yield the expected result, but sometimes its off.

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有时应用得很晚，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，但有时会关闭。

This is what I do. I then use an AVAssetExportSession to create the actual file. but I warn you, the CGAffineTransforms are sometimes applied late, so you'll see a or two of the original before the video transforms. I have no clue why this happens, a different combination of videos will yield the expected result, but sometimes its off.

这篇关于如何使用AVFoundation组合具有不同方向的视频剪辑的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！