Format of CVPixelBuffer

I'm trying to get some clarity on what dictates the format of an CVPixelBuffer. I obtain the buffer for a stream using AVPlayerItemVideoOutput.copyPixelBuffer(), and have seen that on a simulator the format is BGRA, and on a real device it is 420v. What decides on the format of the PixelBuffer?

On a simulator the pixel buffer has the following properties:

    Height = 1080;
    IOSurfaceCoreAnimationCompatibility = 1;
    PixelFormatType = 1111970369;
    Width = 1920;
} propagatedAttachments={
    AlphaChannelIsOpaque = 1;
    CVFieldCount = 1;
    CVImageBufferColorPrimaries = "ITU_R_709_2";
    CVImageBufferTransferFunction = "ITU_R_709_2";
    CVImageBufferYCbCrMatrix = "ITU_R_709_2";
    CVPixelAspectRatio =     {
        HorizontalSpacing = 1;
        VerticalSpacing = 1;
    };
    QTMovieTime =     {
        TimeScale = 90000;
        TimeValue = 210000;
    };
} nonPropagatedAttachments={
}>

And on the real device:

<attributes={
    ExtendedPixelsBottom = 24;
    ExtendedPixelsLeft = 0;
    ExtendedPixelsRight = 16;
    ExtendedPixelsTop = 0;
    PixelFormatDescription =     {
        BitsPerComponent = 8;
        ComponentRange = VideoRange;
        ContainsAlpha = 0;
        ContainsGrayscale = 0;
        ContainsRGB = 0;
        ContainsYCbCr = 1;
        FillExtendedPixelsCallback = {length = 24, bytes = 0x0000000000000000d886649d010000000000000000000000};
        IOSurfaceCoreAnimationCompatibility = 1;
        IOSurfaceCoreAnimationCompatibilityHTPCOK = 1;
        IOSurfaceOpenGLESFBOCompatibility = 1;
        IOSurfaceOpenGLESTextureCompatibility = 1;
        OpenGLESCompatibility = 1;
        PixelFormat = 875704438;
        Planes =         (
                        {
                BitsPerBlock = 8;
                BlackBlock = {length = 1, bytes = 0x10};
            },
                        {
                BitsPerBlock = 16;
                BlackBlock = {length = 2, bytes = 0x8080};
                HorizontalSubsampling = 2;
                VerticalSubsampling = 2;
            }
        );
    };
} propagatedAttachments={
    CVFieldCount = 1;
    CVImageBufferChromaLocationBottomField = Left;
    CVImageBufferChromaLocationTopField = Left;
    CVImageBufferColorPrimaries = "ITU_R_709_2";
    CVImageBufferTransferFunction = "ITU_R_709_2";
    CVImageBufferYCbCrMatrix = "ITU_R_709_2";
    CVPixelAspectRatio =     {
        HorizontalSpacing = 1;
        VerticalSpacing = 1;
    };
    QTMovieTime =     {
        TimeScale = 90000;
        TimeValue = 1059000;
    };
} nonPropagatedAttachments={
}>