private void prepareFilters()
{
// only convert if needed
if (stream->codec->pix_fmt == AVPixelFormat.AV_PIX_FMT_YUV420P)
{
convert = false;
return;
}
// 1 = SWS_FAST_BILINEAR
// https://www.ffmpeg.org/doxygen/3.1/swscale_8h_source.html#l00056
convCtx = ffmpeg.sws_getContext(stream->codec->width, stream->codec->height, stream->codec->pix_fmt, stream->codec->width, stream->codec->height,
AVPixelFormat.AV_PIX_FMT_YUV420P, 1, null, null, null);
}