AVAssetWriter忽略变换值

Question

我正在使用绑定到AVCaptureSession的现有AVCaptureStillImageOutput来获取静态图像。然后我需要将它们写入AVAssetWriter，最后以1秒的间隔获得充满帧的视频文件。

一切正常，除了在纵向模式下输出视频尺寸。当设备处于横向模式时-一切都很好，因为captureStillImageAsynchronouslyFromConnection生成尺寸为1920x1080 (例如)的CMSampleBuffer，但当设备处于纵向模式时，它仍然会生成相同尺寸(1920x1080)的旋转CMSampleBuffer。我可以旋转AVAssetWriterInput的.transform属性的最终输出视频，它工作得很好，但最终视频有错误的尺寸(1920x1080)，但应该是1080x1920。

我发现这个问题出在captureStillImageAsynchronouslyFromConnection's CMSampleBuffer中，它总是有横向维度。然后，AVAssetWriter的输入忽略配置的宽度和高度，并使用CMSampleBuffer的尺寸。

有谁知道怎么解决这个问题吗？

注意:我知道可以使用vImage或核心图形函数来旋转捕获的缓冲区，但出于性能考虑，我希望避免使用这种方法。我的问题看起来像是iOS中的配置问题或错误...

- (void) setupLongLoopWriter
{
self.currentFragment.filename2 = [VideoCapture getFilenameForNewFragment];
NSString *path = [NSString stringWithFormat:@"%@/%@", [GMConfig getVideoCapturesPath], self.currentFragment.filename2];

CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(self.currentCamera.activeFormat.formatDescription);

CGSize videoWriterFrameSize = CGSizeMake(dimensions.width, dimensions.height);

float rotationAngle = 0.0;

switch ((UIDeviceOrientation)[self.currentFragment.orientation unsignedIntValue])
{
    case UIDeviceOrientationUnknown:
    case UIDeviceOrientationPortrait:
    case UIDeviceOrientationFaceUp:
    case UIDeviceOrientationFaceDown:
        rotationAngle = DEGREES_TO_RADIANS(90);
        videoWriterFrameSize = CGSizeMake(dimensions.height, dimensions.width);
        break;

    case UIDeviceOrientationPortraitUpsideDown:
        rotationAngle = DEGREES_TO_RADIANS(-90.0);
        videoWriterFrameSize = CGSizeMake(dimensions.height, dimensions.width);
        break;

    case UIDeviceOrientationLandscapeLeft:
        rotationAngle = 0.0;
        break;

    case UIDeviceOrientationLandscapeRight:
        rotationAngle = DEGREES_TO_RADIANS(180.0);
        break;
}

    //  NSLog(@"%.0fx%.0f", videoWriterFrameSize.width, videoWriterFrameSize.height);

NSError *error = nil;

self.currentFragment.longLoopWriter = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:path]
                                                       fileType:AVFileTypeQuickTimeMovie
                                                          error:&error];
NSParameterAssert(self.currentFragment.longLoopWriter);

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               AVVideoScalingModeResizeAspect, AVVideoScalingModeKey,
                               [NSNumber numberWithInt:videoWriterFrameSize.width], AVVideoWidthKey,
                               [NSNumber numberWithInt:videoWriterFrameSize.height], AVVideoHeightKey,
                               nil];

AVAssetWriterInput* writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                                                     outputSettings:videoSettings];
writerInput.expectsMediaDataInRealTime = YES;

if (rotationAngle != 0.0)
    writerInput.transform = CGAffineTransformMakeRotation (rotationAngle);


NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                                                       [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];

self.currentFragment.longLoopWriterAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];

NSParameterAssert(writerInput);
NSParameterAssert([self.currentFragment.longLoopWriter canAddInput:writerInput]);


[self.currentFragment.longLoopWriter addInput:writerInput];

if( [self.currentFragment.longLoopWriter startWriting] == NO )
    NSLog(@"Failed to start long loop writing!");

[self.currentFragment.longLoopWriter startSessionAtSourceTime:kCMTimeZero];
}

- (void) captureLongLoopFrame
{
if ([GMConfig sharedConfig].longLoopFrameDuration == 0.0) {
    [self.longLoopCaptureTimer invalidate];
    self.longLoopCaptureTimer = nil;

    return;
}

if (self.captureSession.isRunning == NO || self.currentFragment.longLoopWriterAdaptor == nil)
    return;

[self.shutterOutput captureStillImageAsynchronouslyFromConnection:[self.shutterOutput.connections objectAtIndex:0]
                                                completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {
    if (imageDataSampleBuffer != NULL && error == nil) {
        /*
        CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(CMSampleBufferGetFormatDescription(imageDataSampleBuffer));
        CGSize videoWriterFrameSize = CGSizeMake(dimensions.width, dimensions.height);

        NSLog(@"Image buffer size: %.0fx%.0f", videoWriterFrameSize.width, videoWriterFrameSize.height);
        */

        double offset = [[NSDate date] timeIntervalSinceDate:self.currentFragment.start];
        CMTime presentationTime = CMTimeMake(offset*1000, 1000);

        CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(imageDataSampleBuffer);




        if (self.currentFragment.longLoopWriterAdaptor.assetWriterInput.readyForMoreMediaData == YES) {
            if( [self.currentFragment.longLoopWriterAdaptor appendPixelBuffer:imageBuffer withPresentationTime:presentationTime] == NO ) {
                NSLog(@"Error adding frame to long loop!");
            }
        }

        NSLog(@"Long loop updated at %0.1f", CMTimeGetSeconds(presentationTime));
    }
}];
}

Answer 1

我只在纵向模式下录制，通过使用AVCaptureConnection上的setVideoOrientation直接从相机获取旋转的像素数据以传递给AVAssetWriter (参见https://developer.apple.com/library/ios/qa/qa1744/_index.html)，我能够避免这个问题。

for (AVCaptureConnection *connection in [videoOutput connections] ) {
            for ( AVCaptureInputPort *port in [connection inputPorts] ) {
                if ( [[port mediaType] isEqual:AVMediaTypeVideo] ) {

                    [connection setVideoOrientation:AVCaptureVideoOrientationPortrait];

                }
            }
}