Convert From AVI in C# | https://docs.conholdate.com/net/convert-from-avi/

avi-to-mp4.cs

// Load the source AVI file
VideoLoadOptions loadOptions = new VideoLoadOptions();
loadOptions.SetVideoConnector(new VideoConnector());
using (Converter converter = new Converter("sample.avi", () => loadOptions))
{
    // Set the convert options for MP4 format
    VideoConvertOptions options = new VideoConvertOptions {
        Format = VideoFileType.Mp4
    };
    // Convert to MP4 format
    converter.Convert("converted.mp4", options);
}

VideoConnector.cs

public class VideoConnector : IVideoConnector
{
    private readonly Dictionary<VideoFileType, Action<FFMpegArgumentOptions>> _optionsMap = new();
    public VideoConnector()
    {
        _optionsMap.Add(VideoFileType.Avi, SetAviConvertOptions);
        _optionsMap.Add(VideoFileType.Flv, SetFlvConvertOptions);
        _optionsMap.Add(VideoFileType.Mkv, SetMkvConvertOptions);
        _optionsMap.Add(VideoFileType.Mp4, SetMp4ConvertOptions);
        _optionsMap.Add(VideoFileType.Wmv, SetWmvConvertOptions);
        _optionsMap.Add(VideoFileType.Mov, SetMovConvertOptions);
        _optionsMap.Add(VideoFileType.Webm, SetWebmConvertOptions);
    }

    public Stream ConvertVideo(Stream sourceStream, VideoConvertOptions convertOptions)
    { 
        var resultStream = new MemoryStream();


        var arguments = FFMpegArguments
            .FromPipeInput(new StreamPipeSource(sourceStream))
            .OutputToPipe(new StreamPipeSink(resultStream), options =>
            {
                if (_optionsMap.ContainsKey(convertOptions.Format))
                {
                    _optionsMap[convertOptions.Format].Invoke(options);
                }
                else
                {
                    throw new InvalidOperationException(
                        $"Conversion to {convertOptions.Format.Extension} is not supported at the moment");
                }
            });
        arguments.ProcessSynchronously();
            
        return resultStream;
    }

    private void SetAviConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("avi");
    }

    private void SetFlvConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("flv");
    }

    private void SetMkvConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("matroska");
    }

    private void SetMp4ConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("mp4");
        options.WithCustomArgument("-movflags empty_moov");
    }

    private void SetWmvConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("asf");
    }

    private void SetMovConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("mov");
        options.WithCustomArgument("-movflags empty_moov");
    }

    private void SetWebmConvertOptions(FFMpegArgumentOptions options)
    {
        options.ForceFormat("webm");
    }

}