将UIImage转换为CMSampleBufferRef [英] Convert UIImage to CMSampleBufferRef

问题描述

我正在使用 AVFoundation 进行视频录制。我必须将视频裁剪为320x280。我正在使用以下代码获取 CMSampleBufferRef 并将其转换为UIImage。

I am doing video recording using AVFoundation. I have to crop the video to 320x280. I am getting the CMSampleBufferRef and converting it to UIImage using the below code.

CGImageRef _cgImage = [self imageFromSampleBuffer:sampleBuffer];
UIImage *_uiImage = [UIImage imageWithCGImage:_cgImage];
CGImageRelease(_cgImage);
_uiImage = [_uiImage resizedImageWithSize:CGSizeMake(320, 280)];

CMSampleBufferRef croppedBuffer = /* NEED HELP WITH THIS */

[_videoInput appendSampleBuffer:sampleBuffer]; 
// _videoInput is a AVAssetWriterInput

imageFromSampleBuffer：方法看起来像这样：

- (CGImageRef) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer // Create a CGImageRef from sample buffer data
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);        // Lock the image buffer

    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);   // Get information of the image
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef newImage = CGBitmapContextCreateImage(newContext);
    CGContextRelease(newContext);

    CGColorSpaceRelease(colorSpace);
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    /* CVBufferRelease(imageBuffer); */  // do not call this!

    return newImage;
}

现在我必须将调整后的图像转换回 CMSampleBufferRef 写入 AVAssetWriterInput 。

Now I have to convert the resized image back to CMSampleBufferRef to write in AVAssetWriterInput.

如何将 UIImage 转换为 CMSampleBufferRef ？

谢谢大家！

推荐答案

虽然你可以创建自己的Core Media示例缓冲从头开始，可能更容易使用 AVPixelBufferAdaptor 。

While you could create your own Core Media sample buffers from scratch, it's probably easier to use a AVPixelBufferAdaptor.

您在inputSettings字典中描述源像素缓冲区格式并将其传递给适配器初始值设定项：

You describe the source pixel buffer format in the inputSettings dictionary and pass that to the adaptor initializer:

NSMutableDictionary* inputSettingsDict = [NSMutableDictionary dictionary];
[inputSettingsDict setObject:[NSNumber numberWithInt:pixelFormat] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];
[inputSettingsDict setObject:[NSNumber numberWithUnsignedInteger:(NSUInteger)(image.uncompressedSize/image.rect.size.height)] forKey:(NSString*)kCVPixelBufferBytesPerRowAlignmentKey];
[inputSettingsDict setObject:[NSNumber numberWithDouble:image.rect.size.width] forKey:(NSString*)kCVPixelBufferWidthKey];
[inputSettingsDict setObject:[NSNumber numberWithDouble:image.rect.size.height] forKey:(NSString*)kCVPixelBufferHeightKey];
[inputSettingsDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString*)kCVPixelBufferCGImageCompatibilityKey];
[inputSettingsDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey];
AVAssetWriterInputPixelBufferAdaptor* pixelBufferAdapter = [[AVAssetWriterInputPixelBufferAdaptor alloc] initWithAssetWriterInput:assetWriterInput sourcePixelBufferAttributes:inputSettingsDict];

然后，您可以将CVPixelBuffers附加到您的适配器：

You can then append CVPixelBuffers to your adaptor:

[pixelBufferAdapter appendPixelBuffer:completePixelBuffer withPresentationTime:pixelBufferTime]

pixelbufferAdaptor接受CVPixelBuffers，因此您必须将UIImages转换为pixelBuffers，如下所述： https://stackoverflow.com/a/ 3742212/100848

将 UIImage 的 CGImage 属性传递给 newPixelBufferFromCGImage 。

The pixelbufferAdaptor accepts CVPixelBuffers, so you have to convert your UIImages to pixelBuffers, which is described here: https://stackoverflow.com/a/3742212/100848
Pass the CGImage property of your UIImage to newPixelBufferFromCGImage.

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