如何选择与AVAssetReader一起使用的像素格式类型(kCVPixelBufferPixelFormatTypeKey)？

Question

我们正在使用AVAssetReader和使用AVAssetWriter的视频编码中AVAssetWriter提到的样式- CRASHES基本上是从视频库/资产库中读取视频,然后以不同的比特率写入以减小其大小(用于最终的网络上传) .

让它为我们工作的诀窍是kCVPixelBufferPixelFormatTypeKey在outputSettingson中指定一个键和值AVAssetReaderTrackOutput,如下所示:

NSDictionary *outputSettings = [NSDictionary 
    dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                  forKey:(id)kCVPixelBufferPixelFormatTypeKey];     
readerTrackOutput = 
    [[AVAssetReaderTrackOutput alloc] initWithTrack:src_track 
                                     outputSettings:outputSettings];

所以基本上我们使用kCVPixelFormatType_32BGRA了kCVPixelBufferPixelFormatTypeKey键的值.

但显然我们可以选择许多可能的像素格式类型.在iOS 6.0.1 iPhone设备上运行技术问答QA1501:核心视频 - 可用像素格式中记录的代码,以下是它显示的支持像素格式类型列表:

Core Video Supported Pixel Format Types:
Core Video Pixel Format Type: 32
Core Video Pixel Format Type: 24
Core Video Pixel Format Type: 16
Core Video Pixel Format Type (FourCC): L565
Core Video Pixel Format Type (FourCC): 2vuy
Core Video Pixel Format Type (FourCC): yuvs
Core Video Pixel Format Type (FourCC): yuvf
Core Video Pixel Format Type: 40
Core Video Pixel Format Type (FourCC): L008
Core Video Pixel Format Type (FourCC): 2C08
Core Video Pixel Format Type (FourCC): r408
Core Video Pixel Format Type (FourCC): v408
Core Video Pixel Format Type (FourCC): y408
Core Video Pixel Format Type (FourCC): y416
Core Video Pixel Format Type (FourCC): BGRA
Core Video Pixel Format Type (FourCC): b64a
Core Video Pixel Format Type (FourCC): b48r
Core Video Pixel Format Type (FourCC): b32a
Core Video Pixel Format Type (FourCC): b16g
Core Video Pixel Format Type (FourCC): R10k
Core Video Pixel Format Type (FourCC): v308
Core Video Pixel Format Type (FourCC): v216
Core Video Pixel Format Type (FourCC): v210
Core Video Pixel Format Type (FourCC): v410
Core Video Pixel Format Type (FourCC): r4fl
Core Video Pixel Format Type (FourCC): grb4
Core Video Pixel Format Type (FourCC): rgg4
Core Video Pixel Format Type (FourCC): bgg4
Core Video Pixel Format Type (FourCC): gbr4
Core Video Pixel Format Type (FourCC): 420v
Core Video Pixel Format Type (FourCC): 420f
Core Video Pixel Format Type (FourCC): 411v
Core Video Pixel Format Type (FourCC): 411f
Core Video Pixel Format Type (FourCC): 422v
Core Video Pixel Format Type (FourCC): 422f
Core Video Pixel Format Type (FourCC): 444v
Core Video Pixel Format Type (FourCC): 444f
Core Video Pixel Format Type (FourCC): y420
Core Video Pixel Format Type (FourCC): f420
Core Video Pixel Format Type (FourCC): a2vy
Core Video Pixel Format Type (FourCC): L00h
Core Video Pixel Format Type (FourCC): L00f
Core Video Pixel Format Type (FourCC): 2C0h
Core Video Pixel Format Type (FourCC): 2C0f
Core Video Pixel Format Type (FourCC): RGhA
Core Video Pixel Format Type (FourCC): RGfA

即使kCVPixelFormatType_32BGRA为我们工作(至少看似),我们仍然很好奇是否有比上面列表更好的选择.我们应该如何选择正确的像素格式类型给我们？

Answer 1

您可以尝试不同的设置并比较性能。以不同的像素格式向编码器提供缓冲器可能会导致编码性能的差异。硬件加速编码器通常使用“420v”。

另请参阅在 iOS 上捕获视频时查询最佳像素格式？