write audio to memorystream from file

I'm trying to send this file to the outputstream but cannot figure out why it spits out basically an empty mp3 file. As you can see I would get an exception closing the stream prematurely so I have commented out for now. Any pointers appreciated.

using (FileStream mp3file = File.OpenRead(newFile))
                {
                    context.Response.AddHeader("content-transfer-encoding", "binary");
                    context.Response.ContentType = "audio/mpeg";
                    MemoryStream memStream = new MemoryStream();
                    byte[] bytes = new byte[mp3file.Length];
                    memStream.SetLength(mp3file.Length);
                    mp3file.Read(memStream.GetBuffer(), 0, (int)mp3file.Length);
                    memStream.Write(bytes, 0, (int)mp3file.Length);
                    //mp3file.Close();
                    memStream.WriteTo(context.Response.OutputStream);
                    //memStream.Close();

                }

This part is the problem:

 byte[] bytes = new byte[mp3file.Length];
 ...
 // Here you're reading into the memory stream buffer...
 mp3file.Read(memStream.GetBuffer(), 0, (int)mp3file.Length);
 // And here you're overwriting it with the byte array full of zeroes!
 memStream.Write(bytes, 0, (int)mp3file.Length);

You shouldn't assuming that a single call to Read will actually read everything anyway though. It's not clear which version of .NET you're using, but if you're using .NET 4 or higher, you can use Stream.CopyTo to make it simpler.

It's also unclear why you're using a MemoryStream at all. Why don't you just copy straight to the output stream?

mp3File.CopyTo(context.Response.OutputStream);

Or if you're using an older version of .NET:

byte[] buffer = new byte[16 * 1024]; // For exmaple...
int bytesRead;
while ((bytesRead = mp3File.Read(buffer, 0, buffer.Length)) > 0)
{
    context.Response.OutputStream.Write(buffer, 0, bytesRead);
}

(This is pretty much the equivalent of CopyTo.)