Merge two or more mp3 files in C# using naudio library

mashup.cs

    /// <summary>
    /// Creates a mashup of two or more mp3 files by using naudio
    /// </summary>
    /// <param name="files">Name of files as an string array</param>
    /// These files should be existing in a temporay folder
    /// <returns>The path of mashed up mp3 file</returns>
    public static string CreateMashup (string[] files) {
        // because there is no mash up with less than 2 files
        if (files.Count () < 2) {
            throw new Exception ("Not enough files selected!");
        }

        try {
            // Create a mixer object
            // This will be used for merging files together
            var mixer = new WaveMixerStream32 {
                AutoStop = true
            };

            // Set the path to store the mashed up output file
            var outputFile = Path.Combine (Path.GetTempPath (),
                ConfigurationManager.AppSettings["OutputDirName"],
                Guid.NewGuid ().ToString () + ".mp3");

            foreach (var file in files) {
                // for each file -
                // check if it exists in the temp folder
                var filePath = Path.Combine (Path.GetTempPath (),
                    ConfigurationManager.AppSettings["InputDirName"], file + ".mp3");
                if (File.Exists (filePath)) {
                    // create mp3 reader object
                    var reader = new Mp3FileReader (filePath);

                    // create a wave stream and a channel object
                    var waveStream = WaveFormatConversionStream.CreatePcmStream (reader);
                    var channel = new WaveChannel32 (waveStream) {
                        //Set the volume
                        Volume = 0.5f
                    };

                    // add channel as an input stream to the mixer
                    mixer.AddInputStream (channel);
                }
            }

            // convert wave stream from mixer to mp3
            var wave32 = new Wave32To16Stream (mixer);
            var mp3Writer = new LameMP3FileWriter (outputFile, wave32.WaveFormat, 128);
            wave32.CopyTo (mp3Writer);

            // close all streams
            wave32.Close ();
            mp3Writer.Close ();

            // return the mashed up file path
            return outputFile;
        } catch (Exception) {
            // TODO: handle exception
            throw;
        }
    }

What a pity that I have not used naudio library. But I usually merge videos or audios using Joyoshare Video Joiner. Because it supports various media formats and merging videos/audios in the same format losslessly and seamlessly. What's more, it can allow me to cut and edit my files, which satisfies me well.

I don't have any idea why I couldn't install NAudio package on my C# project. I faced with this error:
"Could not install package 'NAudio.Core 2.0.0'. You are trying to install this package into a project that targets '.NETFramework,Version=v4.0', but the package does not contain any assembly references or content files that are compatible with that framework..."
Do you know what is the proper version of .NetFramework for this package?
Thank you in advance.

@ShiliSaghi When I created this app, the version I used for .Net was 4.6.1. See here - https://github.com/gautamdhameja/mtf-mashup/blob/master/src/mashup/mtf-mashup.api/mtf-mashup.api.csproj#L18
The NAudio version I was using was 1.8.3 - https://github.com/gautamdhameja/mtf-mashup/blob/master/src/mashup/mtf-mashup.api/mtf-mashup.api.csproj#L95

Also, here if the full code available for reference - https://github.com/gautamdhameja/mtf-mashup/tree/master/src/mashup
Hope this helps.