/// <exception cref="DecoderException"></exception>
public static DecodedVideoScaler Create(DecodedVideoFrameParameters decodedVideoFrameParms, TransformParameters transformParms)
{
if (decodedVideoFrameParms == null)
{
throw new ArgumentNullException(nameof(decodedVideoFrameParms));
}
if (transformParms == null)
{
throw new ArgumentNullException(nameof(transformParms));
}
int sourceLeft = 0;
int sourceTop = 0;
int sourceWidth = decodedVideoFrameParms.Width;
int sourceHeight = decodedVideoFrameParms.Height;
int scaledWidth = decodedVideoFrameParms.Width;
int scaledHeight = decodedVideoFrameParms.Height;
if (!transformParms.Region.IsEmpty)
{
sourceLeft = transformParms.Region.Left;
sourceTop = transformParms.Region.Top;
sourceWidth = transformParms.Region.Width;
sourceHeight = transformParms.Region.Height;
}
if (!transformParms.TargetSize.IsEmpty)
{
scaledWidth = transformParms.TargetSize.Width;
scaledHeight = transformParms.TargetSize.Height;
ScalingPolicy scalingPolicy = transformParms.ScalePolicy;
float srcAspectRatio = (float)sourceWidth / sourceHeight;
float destAspectRatio = (float)scaledWidth / scaledHeight;
if (scalingPolicy == ScalingPolicy.Auto)
{
float relativeChange = Math.Abs(srcAspectRatio - destAspectRatio) / srcAspectRatio;
scalingPolicy = relativeChange > MaxAspectRatioError
? ScalingPolicy.RespectAspectRatio
: ScalingPolicy.Stretch;
}
if (scalingPolicy == ScalingPolicy.RespectAspectRatio)
{
if (destAspectRatio < srcAspectRatio)
{
scaledHeight = sourceHeight * scaledWidth / sourceWidth;
}
else
{
scaledWidth = sourceWidth * scaledHeight / sourceHeight;
}
}
}
FFmpegPixelFormat pixelFormat = ToFFmpegPixelFormat(transformParms.PixelFormat);
FFmpegScalingQuality scaleQuality = ToFFmpegScaleQuality(transformParms.ScaleQuality);
int resultCode = FFmpegVideoPInvoke.CreateVideoScaler
(
sourceLeft, sourceTop, sourceWidth, sourceHeight,
decodedVideoFrameParms.PixelFormat,
scaledWidth, scaledHeight,
pixelFormat, scaleQuality,
out var handle
);
if (resultCode != 0)
{
throw new DecoderException(@"An error occurred while creating scaler, code: {resultCode}");
}
return(new DecodedVideoScaler(handle, scaledWidth, scaledHeight, transformParms.PixelFormat));
}