VideoFrameConverter.cs

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using FFmpeg.AutoGen;


namespace cavapa
{
    public sealed unsafe class VideoFrameConverter : IDisposable
    {
        private readonly IntPtr _convertedFrameBufferPtr;
        private readonly Size _destinationSize;
        private readonly byte_ptrArray4 _dstData;
        private readonly int_array4 _dstLinesize;
        private readonly SwsContext* _pConvertContext;

        public VideoFrameConverter(Size sourceSize, AVPixelFormat sourcePixelFormat,
            Size destinationSize, AVPixelFormat destinationPixelFormat)
        {
            _destinationSize = destinationSize;
         
                _pConvertContext = ffmpeg.sws_getContext(sourceSize.Width, sourceSize.Height, sourcePixelFormat,
                destinationSize.Width,
                destinationSize.Height, destinationPixelFormat,
                ffmpeg.SWS_FAST_BILINEAR, null, null, null);
            if (_pConvertContext == null) throw new ApplicationException("Could not initialize the conversion context.");

            var convertedFrameBufferSize = ffmpeg.av_image_get_buffer_size(destinationPixelFormat, destinationSize.Width, destinationSize.Height, 1);
            _convertedFrameBufferPtr = Marshal.AllocHGlobal(convertedFrameBufferSize);
            _dstData = new byte_ptrArray4();
            _dstLinesize = new int_array4();

            ffmpeg.av_image_fill_arrays(ref _dstData, ref _dstLinesize, (byte*) _convertedFrameBufferPtr, destinationPixelFormat, destinationSize.Width, destinationSize.Height, 1);
        }

        public void Dispose()
        {
            Marshal.FreeHGlobal(_convertedFrameBufferPtr);
            ffmpeg.sws_freeContext(_pConvertContext);
        }

        public AVFrame Convert(AVFrame sourceFrame)
        {
            ffmpeg.sws_scale(_pConvertContext, sourceFrame.data, sourceFrame.linesize, 0, sourceFrame.height, _dstData, _dstLinesize);

            var data = new byte_ptrArray8();
            data.UpdateFrom(_dstData);
            var linesize = new int_array8();
            linesize.UpdateFrom(_dstLinesize);

            return new AVFrame
            {
                data = data,
                linesize = linesize,
                width = _destinationSize.Width,
                height = _destinationSize.Height
            };
        }
    }
}