AVAssetWriterInputPixelBufferAdaptor返回空像素缓冲池

Question

我确信我的buffer属性出了问题，但我不清楚是什么问题--没有很好的文档记录，所以我猜是基于CVPixelBufferPoolCreate --而Core Foundation对我来说几乎是一本封闭的书。

    // "width" and "height" are const ints
    CFNumberRef cfWidth = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &width);
    CFNumberRef cfHeight = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &height);

    CFStringRef keys[] = {
        kCVPixelBufferWidthKey,
        kCVPixelBufferHeightKey,
        kCVPixelBufferCGImageCompatibilityKey
    };
    CFTypeRef values[] = {
        cfWidth,
        cfHeight,
        kCFBooleanTrue
    };
    int numValues = sizeof(keys) / sizeof(keys[0]);

    CFDictionaryRef bufferAttributes = CFDictionaryCreate(kCFAllocatorDefault, 
                                                          (const void **)&keys, 
                                                          (const void **)&values,
                                                          numValues,
                                                          &kCFTypeDictionaryKeyCallBacks,
                                                          &kCFTypeDictionaryValueCallBacks
                                                          );

    AVAssetWriterInputPixelBufferAdaptor *adaptor = [[AVAssetWriterInputPixelBufferAdaptor 
                                                      assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
                                                      sourcePixelBufferAttributes:(NSDictionary*)bufferAttributes] retain];
    CVPixelBufferPoolRef bufferPool = adaptor.pixelBufferPool;
    NSParameterAssert(bufferPool != NULL); // fails

Answer 1

当pixelBufferPool返回null时，请检查以下内容：

1. AVAssetsWriter的输出文件不存在。2.在AVAssetsWriter上调用startSessionAtTime:之后使用像素缓冲区。3. AVAssetWriterInput和AVAssetWriterInputPixelBufferAdaptor设置正确。4.现在使用appendPixelBuffer的时间并不相同。

Answer 2

我也遇到了同样的问题，我想这可能是因为你没有正确配置你的AVAssetWriterInput。我的游泳池开始工作后，我做了这件事。特别是，除非我以AVVideoCompressionPropertiesKey格式提供数据，否则该池不会为我提供像素缓冲区。首先，创建并完全配置AVAssetWriter (在/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVVideoSettings.h中查找outputSettings和compressionSettings的键和值)：

NSError * err = 0;
AVAssetWriter * outputWriter = [AVAssetWriter
    assetWriterWithURL: [NSURL fileURLWithPath:outputPath]
              fileType: AVFileTypeAppleM4V
                 error: & err];

NSMutableDictionary * outputSettings
    = [[NSMutableDictionary alloc] init];
[outputSettings setObject: AVVideoCodecH264
                   forKey: AVVideoCodecKey];
[outputSettings setObject: [NSNumber numberWithInt: width_]
                   forKey: AVVideoWidthKey];
[outputSettings setObject: [NSNumber numberWithInt: height_]
                   forKey: AVVideoHeightKey];

NSMutableDictionary * compressionProperties
    = [[NSMutableDictionary alloc] init];
[compressionProperties setObject: [NSNumber numberWithInt: 1000000]
                          forKey: AVVideoAverageBitRateKey];
[compressionProperties setObject: [NSNumber numberWithInt: 16]
                          forKey: AVVideoMaxKeyFrameIntervalKey];
[compressionProperties setObject: AVVideoProfileLevelH264Main31
                          forKey: AVVideoProfileLevelKey];

[outputSettings setObject: compressionProperties
                   forKey: AVVideoCompressionPropertiesKey];

AVAssetWriterInput * writerInput = [AVAssetWriterInput
    assetWriterInputWithMediaType: AVMediaTypeVideo
                   outputSettings: outputSettings];

[compressionProperties release];
[outputSettings release];

创建像素缓冲区适配器：

NSMutableDictionary * pixBufSettings = [[NSMutableDictionary alloc] init];
[pixBufSettings setObject: [NSNumber numberWithInt: kCVPixelFormatType_32BGRA]
                   forKey: (NSString *) kCVPixelBufferPixelFormatTypeKey];
[pixBufSettings setObject: [NSNumber numberWithInt: width_]
                   forKey: (NSString *) kCVPixelBufferWidthKey];
[pixBufSettings setObject: [NSNumber numberWithInt: height_]
                   forKey: (NSString *) kCVPixelBufferHeightKey];

AVAssetWriterInputPixelBufferAdaptor * outputPBA =
    [AVAssetWriterInputPixelBufferAdaptor
    assetWriterInputPixelBufferAdaptorWithAssetWriterInput: outputInput
                               sourcePixelBufferAttributes: nil];

然后使用以下命令从其池中检索像素缓冲区：

CVReturn res = CVPixelBufferPoolCreatePixelBuffer (NULL
    , [outputPBA pixelBufferPool]
    , & outputFrame);

Answer 3

根据文档：

“在关联的AVAssetWriter对象上首次调用startSessionAtTime:之前，此属性为NULL。”

因此，如果您太早尝试访问池，它将为NULL。我自己才刚刚学到这些东西，所以我现在不能详细说明。