/// <summary>
/// Builds the <see cref="AV1ConfigBox"/> for the specified image.
/// </summary>
/// <param name="image">The image.</param>
/// <returns></returns>
public static AV1ConfigBox Build(CompressedAV1Image image)
{
if (image is null)
{
ExceptionUtil.ThrowArgumentNullException(nameof(image));
}
bool chromaSubsamplingX;
bool chromaSubsamplingY;
switch (image.Format)
{
case YUVChromaSubsampling.Subsampling400:
case YUVChromaSubsampling.Subsampling420:
chromaSubsamplingX = true;
chromaSubsamplingY = true;
break;
case YUVChromaSubsampling.Subsampling422:
chromaSubsamplingX = true;
chromaSubsamplingY = false;
break;
case YUVChromaSubsampling.Subsampling444:
// The AV1 Bitstream & Decoding Process specification requires chroma sub-sampling
// to be false when the NCLX Identity matrix coefficient is used.
case YUVChromaSubsampling.IdentityMatrix:
chromaSubsamplingX = false;
chromaSubsamplingY = false;
break;
default:
throw new InvalidOperationException($"Unknown { nameof(YUVChromaSubsampling) } value: { image.Format }");
}
return(new AV1ConfigBox()
{
SeqProfile = GetSeqProfile(image.Format),
SeqLevelIdx0 = GetSeqLevelIdx0(image),
SeqTier0 = false,
HighBitDepth = false,
TwelveBit = false,
Monochrome = image.Format == YUVChromaSubsampling.Subsampling400,
ChromaSubsamplingX = chromaSubsamplingX,
ChromaSubsamplingY = chromaSubsamplingY,
ChromaSamplePosition = ChromaSamplePosition.Unknown
});
}
private static SequenceLevel GetSeqLevelIdx0(CompressedAV1Image image)
{
int width = image.Width;
int height = image.Height;
long imageSize = (long)width * height;
// These values are from the Annex A.3 table: https://aomediacodec.github.io/av1-spec/av1-spec.pdf
if (imageSize <= 147456 && width <= 2048 && height <= 1152)
{
return(SequenceLevel.TwoPointZero);
}
else if (imageSize <= 278784 && width <= 2816 && height <= 1584)
{
return(SequenceLevel.TwoPointOne);
}
else if (imageSize <= 665856 && width <= 4352 && height <= 2448)
{
return(SequenceLevel.ThreePointZero);
}
else if (imageSize <= 1065024 && width <= 5504 && height <= 3096)
{
return(SequenceLevel.ThreePointOne);
}
else if (imageSize <= 2359296 && width <= 6144 && height <= 3456)
{
// 4.0 and 4.1 support the same image sizes.
return(SequenceLevel.FourPointOne);
}
else if (imageSize <= 8912896 && width <= 8192 && height <= 4352)
{
// 5.0-5.3 support the same image sizes.
// The AV1 specification states that 5.1 is the baseline profile
// https://aomediacodec.github.io/av1-avif/#baseline-profile
return(SequenceLevel.FivePointOne);
}
else
{
// If the image is larger than the defined profile values,
// return the "Maximum parameters" value.
return(SequenceLevel.MaximumParameters);
}
}
