Using hardware acceleration

Since version 3.1.0 there is a possibility to use hardware acceleration.

/// <summary>
///     Use hardware acceleration. This option set -threads to 1 for compatibility reasons. This should be use with proper codec (e.g. -c:v h264_nvencorh264_cuvid)
/// </summary>
/// <param name="hardwareAccelerator">Hardware accelerator. List of all accelerators available for your system - "ffmpeg -hwaccels"</param>
/// <param name="decoder">Codec using to decode input video.</param>
/// <param name="encoder">Codec using to encode output video.</param>
/// <param name="device">Number of device (0 = default video card) if more than one video card.</param>
/// <returns>IConversion object</returns>
IConversion UseHardwareAcceleration(HardwareAccelerator hardwareAccelerator, VideoCodec decoder, VideoCodec encoder, int device = 0);
gpu vs cpu conversion

You can read more at official ffmpeg wiki.