If you think audio streams are redundant or you have multiple video streams and you need only default one you can use ExtractVideo snippet. It creates new file with only one video stream:

string output = Path.ChangeExtension(Path.GetTempFileName(), Path.GetExtension(Resources.Mp4WithAudio));
var conversion = FFmpeg.Conversions.FromSnippet.ExtractVideo(Resources.Mp4WithAudio, output);
await conversion.Start();