AVAssetWriter可以透明地写入文件吗?

问题描述

我使用AVAssetWriter编写的每个文件都有黑色背景，如果我包含的图像没有填充整个渲染区域.有透明的书写方式吗?这是我用来获取像素缓冲区的方法:

Every file I write with AVAssetWriter has a black background, if the images I include do not fill the entire render area. Is there any way to write with transparency? Here's the method I use to get the pixel buffer:

- (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image {

    CGSize size = self.renderSize;

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                             nil];
    CVPixelBufferRef pxbuffer = NULL;
    CVPixelBufferPoolCreatePixelBuffer(NULL, self.adaptor.pixelBufferPool, &pxbuffer);

    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
                                          size.width,
                                          size.height,
                                          kCVPixelFormatType_32ARGB,
                                          (__bridge CFDictionaryRef) options,
                                          &pxbuffer);


    if (status != kCVReturnSuccess){
        NSLog(@"Failed to create pixel buffer");
    }

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, size.width,
                                                 size.height, 8, 4*size.width, rgbColorSpace,
                                                 (CGBitmapInfo)kCGImageAlphaPremultipliedFirst);

    CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

以及AVAssetWriter代码:

And the AVAssetWriter code:

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

AVAssetWriterInput* videoWriterInput = [AVAssetWriterInput
                                        assetWriterInputWithMediaType:AVMediaTypeVideo
                                        outputSettings:videoSettings];

NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys:
                                  [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];
self.adaptor = [AVAssetWriterInputPixelBufferAdaptor
                    assetWriterInputPixelBufferAdaptorWithAssetWriterInput:videoWriterInput
                    sourcePixelBufferAttributes:bufferAttributes];

buffer = [self pixelBufferFromCGImage:[stickerImage CGImage]];

BOOL append_ok = YES;
    int j = 0;
    while (append_ok && j < totalFrames) {
        if (self.adaptor.assetWriterInput.readyForMoreMediaData)  {

            CMTime frameTime = CMTimeMake(frameCount,(int32_t) fps);
            append_ok = [self.adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];
            if(!append_ok){
                NSError *error = self.assetWriter.error;
                if(error!=nil) {
                    NSLog(@"Unresolved error %@,%@.", error, [error userInfo]);
                }
            }
        }
        else {
            printf("adaptor not ready %d, %d\n", frameCount, j);
            [NSThread sleepForTimeInterval:0.1];
        }
        j++;
        frameCount++;
    }
    if (!append_ok) {
        printf("error appending image %d times %d\n, with error.", frameCount, j);
    }

推荐答案

简而言之，这是不可能的. AVAssetWriter使用h264视频编解码器输出. h264视频编解码器不支持Alpha通道，因此很遗憾，您不走运.

In short, This is not possible. AVAssetWriter outputs using the h264 video codec. The h264 video codec does not support an alpha channel, so you are unfortunately out of luck.

一种更复杂的解决方案将涉及将alpha通道(透明度)渲染为h264灰度编码的视频，并在观看时将摩擦和alpha信息重新组合在一起.

A more involved solution would involve rendering the alpha channel (transparency) into a grayscale h264 encoded video and compositiong the rub and alpha information back together when viewing.

这篇关于AVAssetWriter可以透明地写入文件吗?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！