如何使用 NAudio/SoundTouch 在 ASP.NET MVC 5 中流式传输 MP3？

Question

I am completely new to working with audio. I eventually want to stream an MP3 to a web page and allow user to alter the tempo. I got a HTML5 audio element set up and it can stream a MP3 fine. I can import the MP3 into NAudio.AudioFileReader and stream that to the page and that also works fine using the following code:

string fn = Server.MapPath("~/Uploads/Music/" + filename);
AudioFileReader reader = new AudioFileReader(fn);
MemoryStream outputStream = new MemoryStream();

using (NAudio.Wave.WaveFileWriter waveFileWriter = new WaveFileWriter(outputStream, reader.WaveFormat))
{
    byte[] bytes = new byte[reader.Length];
    reader.Position = 0;
    reader.Read(bytes, 0, (int)reader.Length);
    waveFileWriter.Write(bytes, 0, bytes.Length);
    waveFileWriter.Flush();
}

return File(outputStream.ToArray(), "audio/mp3");

I'm not even sure if this is the proper way to do this, but I modified some code I found online and this does work. However, when looking at the NAudio Varispeed demo which integrates the SoundTouch library and trying to incorporate it, it no longer works.

I modified my code like this:

string fn = Server.MapPath("~/Uploads/Music/" + filename);
AudioFileReader reader = new AudioFileReader(fn);
bool useTempo = true;
VarispeedSampleProvider speedControl = new VarispeedSampleProvider(reader, 100, new SoundTouchProfile(useTempo, false));
MemoryStream outputStream = new MemoryStream();

using (NAudio.Wave.WaveFileWriter waveFileWriter = new WaveFileWriter(outputStream, reader.WaveFormat))
{
    byte[] bytes = new byte[reader.Length];
    speedControl.Read(bytes.Select(b => (float)Convert.ToDouble(b)).ToArray(), 0, (int)reader.Length);
    waveFileWriter.Write(bytes, 0, bytes.Length);
    waveFileWriter.Flush();
}

return File(outputStream.ToArray(), "audio/mp3");

It builds and appears like it's working but when I hit play, I get no audio. What am I doing wrong here? Is this not even a good way to accomplish what I want?

Answer 1

You are reading into a temporary array (created by ToArray ), so the audio you read is lost.

Instead, declare a float[] , read into that, and then write the contents of that into the waveFileWriter .

Also, it is very important to use the return value from Read which will indicate the number of samples actually written into the array.