AVAssetWriter Woes

编程问答 2022-04-26

问题描述

| 我正在尝试使用AVAssetWriter将CGImages写入文件以根据图像创建视频。 我已经在模拟器上以三种不同的方式成功完成了此操作，但是每种方法在运行iOS 4.3的iPhone 4上均失败。 所有这些都与像素缓冲区有关。 我的第一种方法是仅根据需要创建像素缓冲区，而无需使用池。可以，但是在设备上占用的内存过多。 我的第二种方法是使用推荐的AVAssetWriterInputPixelBufferAdaptor，然后使用CVPixelBufferPoolCreatePixelBuffer从适配器pixelBufferPool中提取像素缓冲区。 这也可以在模拟器上运行，但是在设备上将失败，因为适配器的像素缓冲池从未分配。我没有收到任何错误消息。 最后，我尝试使用CVPixelBufferPoolCreate通过自己的像素缓冲池创建。这在模拟器中也可以使用，但是在设备上，一切正常，直到我尝试用appendPixelBuffer追加像素缓冲区，但每次都失败。 我在网络上发现的信息很少。我已经根据找到的示例创建了代码，但是现在已经没有运气了。如果任何人都有成功使用AVAssetWriter进行此操作的经验，请看一下，如果发现有任何异常，请与我联系。 注意：您将看到注释掉的尝试块。 一，安装 
- (BOOL) openVideoFile: (Nsstring *) path withSize:(CGSize)imageSize {
size = CGSizeMake (480.0,320.0);//imageSize;

NSError *error = nil;
videoWriter = [[AVAssetWriter alloc] initWithURL:
                              [NSURL fileURLWithPath:path] fileType:AVFileTypeQuickTimeMovie
                                                          error:&error];
if (error != nil)
    return NO;

NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                            [NSNumber numberWithDouble:size.width],AVVideoCleanApertureWidthKey,[NSNumber numberWithDouble:size.height],AVVideoCleanApertureHeightKey,[NSNumber numberWithInt:10],AVVideoCleanApertureHorizontalOffsetKey,AVVideoCleanApertureVerticalOffsetKey,nil];


NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                          [NSNumber numberWithInt:1],AVVideoPixelAspectRatioHorizontalSpacingKey,[NSNumber numberWithInt:1],AVVideoPixelAspectRatioVerticalSpacingKey,nil];



NSDictionary *codecSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               //[NSNumber numberWithInt:960000],AVVideoAverageBitRateKey,// [NSNumber numberWithInt:1],AVVideoMaxKeyFrameIntervalKey,videoCleanApertureSettings,AVVideoCleanApertureKey,videoAspectRatioSettings,AVVideoPixelAspectRatioKey,//AVVideoProfileLevelH264Main31,AVVideoProfileLevelKey,nil];

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264,AVVideoCodecKey,codecSettings,AVVideoCompressionPropertiesKey,[NSNumber numberWithDouble:size.width],AVVideoWidthKey,AVVideoHeightKey,nil];
writerInput = [[AVAssetWriterInput
                                    assetWriterInputWithMediaType:AVMediaTypeVideo
                                    outputSettings:videoSettings] retain];
NSMutableDictionary * bufferAttributes = [[NSMutableDictionary alloc] init];
[bufferAttributes setobject: [NSNumber numberWithInt: kCVPixelFormatType_32ARGB]
                   forKey: (Nsstring *) kCVPixelBufferPixelFormatTypeKey];
[bufferAttributes setobject: [NSNumber numberWithInt: 480]
                   forKey: (Nsstring *) kCVPixelBufferWidthKey];
[bufferAttributes setobject: [NSNumber numberWithInt: 320]
                   forKey: (Nsstring *) kCVPixelBufferHeightKey];


//NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32ARGB],kCVPixelBufferPixelFormatTypeKey,nil];
//[bufferAttributes setobject: [NSNumber numberWithInt: 640]
//                   forKey: (Nsstring *) kCVPixelBufferWidthKey];
//[bufferAttributes setobject: [NSNumber numberWithInt: 480]
//                   forKey: (Nsstring *) kCVPixelBufferHeightKey];
adaptor = [[AVAssetWriterInputPixelBufferAdaptor
            assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
            sourcePixelBufferAttributes:nil] retain];

//CVPixelBufferPoolCreate (kcfAllocatorSystemDefault,NULL,(CFDictionaryRef)bufferAttributes,&pixelBufferPool);
//Create buffer pool
NSMutableDictionary*     attributes;
attributes = [NSMutableDictionary dictionary];

int width = 480;
int height = 320;

[attributes setobject:[NSNumber numberWithInt:kCVPixelFormatType_32ARGB] forKey:(Nsstring*)kCVPixelBufferPixelFormatTypeKey];
[attributes setobject:[NSNumber numberWithInt:width] forKey: (Nsstring*)kCVPixelBufferWidthKey];
[attributes setobject:[NSNumber numberWithInt:height] forKey: (Nsstring*)kCVPixelBufferHeightKey];
CVReturn theError = CVPixelBufferPoolCreate(kcfAllocatorDefault,(CFDictionaryRef) attributes,&pixelBufferPool);                                           


NSParameterassert(writerInput);
NSParameterassert([videoWriter canAddInput:writerInput]);
[videoWriter addInput:writerInput];

writerInput.expectsMediaDataInRealTime = YES;

//Start a session:
[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];

buffer = NULL;
lastTime = kCMTimeZero;
presentTime = kCMTimeZero;

return YES;
}
接下来，使用两种方法追加编写器并创建要追加的像素缓冲区。 
- (void) writeImagetoMovie:(CGImageRef)image 
{
    if([writerInput isReadyForMoreMediaData])
    {
//          CMTime frameTime = CMTimeMake(1,20);
//          CMTime lastTime=CMTimeMake(i,20); //i is from 0 to 24 of the loop above
//          CMTime presentTime=CMTimeAdd(lastTime,frameTime);

        buffer = [self pixelBufferFromCGImage:image];
        BOOL success = [adaptor appendPixelBuffer:buffer withPresentationTime:presentTime];
        if (!success) NSLog(@\"Failed to appendPixelBuffer\");
        CVPixelBufferRelease(buffer);

        presentTime = CMTimeAdd(lastTime,CMTimeMake(5,1000));
        lastTime = presentTime;
    }
    else
    {
        NSLog(@\"error - writerInput not ready\");
    }
}

- (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image
{
CVPixelBufferRef pxbuffer;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:YES],kCVPixelBufferCGImageCompatibilityKey,[NSNumber numberWithBool:YES],kCVPixelBufferCGBitmapContextCompatibilityKey,nil];
if (pixelBufferPool == NULL) NSLog(@\"pixelBufferPool is null!\");
CVReturn status = CVPixelBufferPoolCreatePixelBuffer (NULL,pixelBufferPool,&pxbuffer); 
/*if (pxbuffer == NULL) {
    CVReturn status = CVPixelBufferCreate(kcfAllocatorDefault,size.width,size.height,kCVPixelFormatType_32ARGB,(CFDictionaryRef) options,&pxbuffer);

}*/
//NSParameterassert(status == kCVReturnSuccess && pxbuffer != NULL);


CVPixelBufferLockBaseAddress(pxbuffer,0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
//NSParameterassert(pxdata != NULL);

CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata,8,4*size.width,rgbColorSpace,kCGImageAlphaNoneskipFirst);
//NSParameterassert(context);
CGContextConcatCTM(context,CGAffineTransformMakeRotation(0));
CGContextDrawImage(context,CGRectMake(90,10,CGImageGetWidth(image),CGImageGetHeight(image)),image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);

CVPixelBufferUnlockBaseAddress(pxbuffer,0);

return pxbuffer;
}
    

解决方法

        我已经找到解决此问题的方法。 如果要使AVAudioPlayer和AVAssetWriter一起正常运行，则必须具有和音频会话类别为'mixable \'。 您可以使用可混合使用的类别，例如AVAudioSessionCategoryAmbient。 但是，我需要使用AVAudioSessionCategoryPlayAndRecord。 您可以通过实现以下方式将任何类别设置为可混合使用： 
OSStatus propertySetError = 0;

UInt32 allowMixing = true;

propertySetError = AudioSessionSetProperty (
                       kAudioSessionProperty_OverrideCategoryMixWithOthers,// 1
                       sizeof (allowMixing),// 2
                       &allowMixing                                          // 3
                   );
    ,        好吧，首先在创建该适配器对象时需要传递一些“ 3”： 
    NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32BGRA],kCVPixelBufferPixelFormatTypeKey,nil];

AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor
                                                 assetWriterInputPixelBufferAdaptorWithAssetWriterInput:_videoWriterInput
                                                 sourcePixelBufferAttributes:bufferAttributes];
然后将对“ 5”的调用删除，适配器对象中已经创建了一个像素缓冲池，因此只需调用以下命令： 
                CVPixelBufferRef pixelBuffer = NULL;
            CVPixelBufferPoolCreatePixelBuffer(NULL,adaptor.pixelBufferPool,&pixelBuffer);
            CVPixelBufferLockBaseAddress(pixelBuffer,0);

            // ...fill the pixelbuffer here

            CVPixelBufferUnlockBaseAddress(pixelBuffer,0);

            CMTime frameTime = CMTimeMake(frameCount,(int32_t) 30);

            BOOL res = [adaptor appendPixelBuffer:pixelBuffer withPresentationTime:frameTime];
            CVPixelBufferRelease(pixelBuffer);
            CFRelease(sampleBuffer);
我认为应该这样做，在某些时候我也遇到了类似的错误，我通过创建适配器和像素缓冲区来解决它，如下所示。     
avassetwriter