如何将背景图像设置为AVMutableVideoCompositionInstruction

Question

我设置backgroundColor工作正常，但我无法设置背景图像。

AVMutableVideoCompositionInstruction * MainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
MainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero,assetWithMaxTime.duration);
MainInstruction.enablePostProcessing = NO;

MainInstruction.backgroundColor =[UIColor yellowColor].CGColor;

Answer 1

在尝试了几件事之后我终于找到了一种方法。要使其工作，需要使用空白视频/音频轨道。然后将背景图像添加到此空白视频图层。十出口并结合原始资产（视频）和出口资产（资产）并输出最终资产（视频）。

添加叠加层

- (void)addOverlayImage:(UIImage *)overlayImage ToVideo:(AVMutableVideoComposition *)composition inSize:(CGSize)size {
    // 1 - set up the overlay
    CALayer *overlayLayer = [CALayer layer];

    [overlayLayer setContents:(id)[overlayImage CGImage]];
    overlayLayer.frame = CGRectMake(0, 0, size.width, size.height);
    [overlayLayer setMasksToBounds:YES];

    // 2 - set up the parent layer
    CALayer *parentLayer = [CALayer layer];
    CALayer *videoLayer = [CALayer layer];
    parentLayer.frame = CGRectMake(0, 0, size.width, size.height);
    videoLayer.frame = CGRectMake(0, 0, size.width, size.height);
    [parentLayer addSublayer:videoLayer];
    [parentLayer addSublayer:overlayLayer];

    // 3 - apply magic
    composition.animationTool = [AVVideoCompositionCoreAnimationTool
                                 videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
}

- (void)getBackgroundVideoAssetWithcompletion:(void (^)(AVAsset *bgAsset))completionBlock {

    NSString *path = [[NSBundle mainBundle] pathForResource:@"blank_video" ofType:@"mp4"];
    NSURL *trackUrl = [NSURL fileURLWithPath:path];
    AVAsset *asset = [AVAsset assetWithURL:trackUrl];
    AVAssetTrack *track = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

    CMTimeRange range = CMTimeRangeMake(kCMTimeZero, [asset duration]);
    AVMutableComposition* mixComposition = [AVMutableComposition composition];

    AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionVideoTrack insertTimeRange:range ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];


    CGAffineTransform videoTransform = track.preferredTransform;
    CGSize naturalSize = CGSizeApplyAffineTransform(track.naturalSize, videoTransform);
    naturalSize = CGSizeMake(fabs(naturalSize.width), fabs(naturalSize.height));


    AVMutableVideoComposition *composition = [AVMutableVideoComposition videoCompositionWithPropertiesOfAsset:asset];
    UIImage *img = [self imageWithImage:[UIImage imageNamed:@"white_image"] convertToSize:naturalSize];
    [self addOverlayImage:img ToVideo:composition inSize:naturalSize];


    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    instruction.timeRange = range;
    composition.instructions = @[instruction];


    AVAssetExportSession *_assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];
    _assetExport.videoComposition = composition;



    NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"exported-%d.mov", arc4random() % 100000]];
    unlink([exportPath UTF8String]);
    NSURL *exportUrl = [NSURL fileURLWithPath:exportPath];

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

    [_assetExport exportAsynchronouslyWithCompletionHandler:^{

        switch (_assetExport.status) {

            case AVAssetExportSessionStatusFailed:
                 break;

            case AVAssetExportSessionStatusExporting:
                break;

            case AVAssetExportSessionStatusCompleted:{

                dispatch_async(dispatch_get_main_queue(), ^{
                    NSLog(@"Successful!!!");
                    AVAsset *finalAsset = [AVAsset assetWithURL:_assetExport.outputURL];
                    completionBlock(finalAsset);
                });
            }
                break;

            default:
                break;
        }
    }];
}

现在有一个带叠加图像的视频资产。只保留原始视频和导出的视频资产的组合。导出的资产应该是底层，原始应该是顶层。