AVAsset在iOS中使用图像覆盖保存视频废墟视频

Question

我试图将图像叠加和视频合并到一个新的视频文件中。这是我正在使用的代码：

- (void)mergeVideoUrl:(NSURL *)videoURL andOverlayImage:(UIImage *)overlayImage 
{ 
    NSLog(@"%s", __PRETTY_FUNCTION__); 

    // Create an AVURLAsset 
    AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:videoURL options:nil]; 
    AVMutableComposition* mixComposition = [AVMutableComposition composition]; 

    AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; 
    AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
            ofTrack:clipVideoTrack 
            atTime:kCMTimeZero 
            error:nil]; 

    [compositionVideoTrack setPreferredTransform:[[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform]]; 

    CGSize videoSize = [clipVideoTrack naturalSize]; 

    // Get our image layer 
    CALayer *aLayer = [CALayer layer]; 
    aLayer.contents = (id)overlayImage.CGImage; 
    aLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    aLayer.opacity = 1.0; 

    // Sort the layer order 
    CALayer *parentLayer = [CALayer layer]; 
    CALayer *videoLayer = [CALayer layer]; 
    parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    [parentLayer addSublayer:videoLayer]; 
    [parentLayer addSublayer:aLayer]; 

    // Create the composition and add the instructions to insert the layer 
    AVMutableVideoComposition* videoComp = [AVMutableVideoComposition videoComposition]; 
    videoComp.renderSize = videoSize; 
    videoComp.frameDuration = CMTimeMake(1, 30); 
    videoComp.animationTool = [AVVideoCompositionCoreAnimationTool  videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer]; 

    // Instruction 
    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; 
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]); 
    AVAssetTrack *videoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
    AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack]; 
    instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction]; 
    videoComp.instructions = [NSArray arrayWithObject: instruction]; 

    // Export 
    AVAssetExportSession *assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality]; 
    assetExport.videoComposition = videoComp; 

    NSString* videoName = @"mynewwatermarkedvideo.mov"; 

    NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:videoName]; 
    NSURL *exportUrl = [NSURL fileURLWithPath:exportPath]; 

    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) 
    { 
     [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil]; 
    } 

    assetExport.outputFileType = AVFileTypeQuickTimeMovie; 
    assetExport.outputURL = exportUrl; 
    assetExport.shouldOptimizeForNetworkUse = YES; 

    [assetExport exportAsynchronouslyWithCompletionHandler:^(void) 
    { 
     //FINALIZATION CODE HERE 
     NSLog(@"DONE: %@", exportUrl); 
    }]; 
} 

问题是，它拧紧了视频。任何想法为什么？ 我有一种感觉，视频帧的大小可能与它或纵横比有关，如果我设置了(2000,2000)的大小，它似乎工作正常，但有很多黑色边缘。

EDIT ----- 看来，如果我设置CGSize videoSize到2/3例如比320x480或1280x1920然后它可以工作，但是最终的视频右下方有一个黑条。为什么[clipVideoTrack naturalSize]报告的尺寸为1080x1920，但是如果没有使用1280x1920，它会被锁定？我认为这可能是一个转换/作物问题？

EDIT2 ----- 更改AVAssetExportSessionAVAssetExportPresetLowQuality presetName之间，AVAssetExportPresetMediumQuality & AVAssetExportPresetHighestQuality导致不同尺寸的视频。所以我认为这在某种程度上压倒了输出视频帧的大小。

Answer 1

CGSize videoSize = [clipVideoTrack naturalSize]; 

这使您可以记录的尺寸，但你需要看着赛道的prefferedTransform找到记录的方向。您可能会发现视频宽度实际上是“高度”，具体取决于录制过程中设备的保持方式。

我看你把它的组成，但你需要检查它以正确的帧分配给您的CALayers