Streaming audio with WCF

This article will present a way to stream audio with WCF. In my example, I will play a Waveform Audio File Format file (.wav), but my sample should support any well-known audio formats. Note that WCF is not automatically the best streaming service to provide to your clients. Other protocols such as RTSP have better handling of graceful degradation, random seek and so on. This article will only show how you can provide a simple one-direction playback of audio files by using WCF. You can start by cloning the repository I have made public from here:

git@bitbucket.org:toreaurstad/wcfaudiostreamdemo.git

First off, we need to specify a content type of the method that returns a Stream with the audio. This can be achieved by implementing a class that inherits from System.Attribute and implementing IOperationBehavior. The class below sets a content type in its constructor and sets a Formatter of the DispatcherOperation in ApplyDispatchBehavior to the class ContentTypeMessageFormatter.

using System;
using System.ServiceModel.Channels;
using System.ServiceModel.Description;
using System.ServiceModel.Dispatcher;


namespace WcfStreamAudioDemo.Common
{
    public class ContentTypeAttribute : Attribute, IOperationBehavior
    {
        public ContentTypeAttribute(string contentType)
        {
            ContentType = contentType;
        }

        public string ContentType { get; } //readonly auto property

        public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters)
        {
          
        }

        public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation)
        {
            
        }

        public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
        {
            // ReSharper disable once ArrangeThisQualifier
            dispatchOperation.Formatter = new ContentTypeMessageFormatter(dispatchOperation.Formatter, this.ContentType);
        }

        public void Validate(OperationDescription operationDescription)
        {
            
        }

      }
}

The ContentTypeMessageFormatter class is shown below:

using System.ServiceModel.Channels;
using System.ServiceModel.Dispatcher;
using System.ServiceModel.Web;
namespace WcfStreamAudioDemo.Common
{
    public class ContentTypeMessageFormatter : IDispatchMessageFormatter
    {

        private readonly IDispatchMessageFormatter _formatter;
        private readonly string _contentType;

        public ContentTypeMessageFormatter(IDispatchMessageFormatter formatter, string contentType)
        {
            _formatter = formatter;
            _contentType = contentType; 
        }

        public void DeserializeRequest(Message message, object[] parameters)
        {
            _formatter.DeserializeRequest(message, parameters);
        }

        public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result)
        {
            if (!string.IsNullOrEmpty(_contentType))
                WebOperationContext.Current.OutgoingResponse.ContentType = _contentType;
            return _formatter.SerializeReply(messageVersion, parameters, result);
        }

    }
}

Next step is to define a Service Contract in WCF to test this out:

using System.IO;
using System.ServiceModel;
using System.ServiceModel.Web;

namespace WcfStreamAudioDemo.Common
{

    [ServiceContract]
    public interface IAudioServiceContract
    {

        [OperationContract]
        [ContentType("audio/wav")]
        [WebGet(UriTemplate = "media/{trackName}")]
        Stream GetAudio(string trackName);
    }
}

The configuration of the WCF service in web.config sets up streaming by using transferMode set to Streamed on a webHttpBinding.

  <system.serviceModel>

    <services>
      
      <service name="WcfStreamAudioDemo.Host.AudioService">
        <endpoint behaviorConfiguration="RestBehaviorConfig" binding="webHttpBinding" bindingConfiguration="HttpStreaming" contract="WcfStreamAudioDemo.Common.IAudioServiceContract" />
      </service>
    </services>

    <bindings>
      <webHttpBinding>
        <binding name="HttpStreaming" transferMode="Streamed" maxReceivedMessageSize="1000000000" />
      </webHttpBinding>
    </bindings>
    
    <behaviors>

      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, set the values below to false before deployment -->
          <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
     
      <endpointBehaviors>
        <behavior name="RestBehaviorConfig">
          <webHttp />
        </behavior>
      </endpointBehaviors>

    </behaviors>
    <protocolMapping>
        <add binding="basicHttpsBinding" scheme="https" />
    </protocolMapping>    
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  </system.serviceModel>

Finally, to test out this Audio Service you can either enter the url of an audio file the WCF service recognizes into a browser to download the .WAV file or for example use an HTML 5 <audio> element. Here is a sample page I created to test out the Audio service (a simple ASP.NET Web form)!

<%@ Page Language="C#" %>

<script runat="server">

</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Demo Audio Stream wcf</title>
</head>
<body>
<form id="HtmlForm" runat="server">
    <div>
        
        <h3>WCF Sample Audio streaming example</h3>
        
        <p>Playing an audio file (.wav) using a custom WCF IDispatchMessageFormatter with REST (webHttpBinding).</p>
        
        <audio controls>
            <source src="http://localhost/WcfStreamAudioDemo.Host/AudioService.svc/media/Sample" type="audio/wav" />
            <p>Your browser doesn't support HTML5 audio. Here is a <a href="http://localhost/WcfStreamAudioDemo.Host/AudioService.svc/media/Sample.wav">link to the audio</a> instead.</p> 
        </audio>

    </div>
</form>
</body>
</html>