Playing Audio on Android from an HTML5 File

Introduction

Earlier today, I came across a problem. I have been working on an App in Android that displays HTML5 files from the assets folder inside a WebView. One of the big problems with playing Audio in an HTML5 page is that a lot of browsers do not support the <audio> tag; this includes several versions of the WebView control in different versions of Android. The bottom line is that you can't expect standardized results across different versions of Android when using the HTML5 <audio> tag. So we're going to use a workaround that uses the native Android method of playing audio.

Here is a synopsis of the paragraphs below that describe how to implement the code.

• Configuring your WebView control
• Creating an Audio Interface for the HTML5 web page
• Attaching the Audio Interface to the WebView control
• Invoking an Audio Interface function from the HTML5 page using JavaScript

Implementing the Code

Configuring your WebView control

Create a WebView control inside your layout. This is the XML code for the layout I used:

<?xml version="1.0" encoding="utf-8"?>
<WebView  xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/webview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

This is the Java that I used to initially configure the WebView:

 //Configures the WebView during the onCreate method
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    WebView myWebView = (WebView) findViewById(R.id.webview);

    //Set it to a webChromeClient
    myWebView.setWebChromeClient(new WebChromeClient());

    //the default for WebView is that JavaScript isn't enabled in WebView
    myWebView.getSettings().setJavaScriptEnabled(true);

    //the index.html file is placed in the assets folder
    myWebView.loadUrl("file:///android_asset/index.html");
}

Creating an Audio Interface for the HTML5 web page

Next, we're going to create an AudioInterface Java class to play audio MP3s from the assets folder.

Create a new Java Class and call it "AudioInterface.Java"

Here is the Java code for the class:

import java.io.IOException;
import android.content.Context;
import android.content.res.AssetFileDescriptor;
import android.media.MediaPlayer;
import android.webkit.JavascriptInterface;

public class AudioInterface {
	Context mContext;

	AudioInterface(Context c) {
		mContext = c;
	}
	
	//Play an audio file from the webpage
	@JavascriptInterface
	public void playAudio(String aud) { //String aud - file name passed 
	                                    //from the JavaScript function
		final MediaPlayer mp;

			  try {
				  AssetFileDescriptor fileDescriptor = 
				  		mContext.getAssets().openFd(aud);
              	                  mp = new MediaPlayer();
              	                  mp.setDataSource(fileDescriptor.getFileDescriptor(), 
              	                  fileDescriptor.getStartOffset(), 
              	                  fileDescriptor.getLength());
              	                  fileDescriptor.close();
              	                  mp.prepare();
              	                  mp.start();
			  } catch (IllegalArgumentException e) {
	                          // TODO Auto-generated catch block
	                          e.printStackTrace();
	          	  } catch (IllegalStateException e) {
	                          // TODO Auto-generated catch block
	                          e.printStackTrace();
	          	  } catch (IOException e) {
	                          // TODO Auto-generated catch block
	                          e.printStackTrace();
	          } 
	}
}

The above code creates a public method that accepts a string argument which is used as the URL for the mp3 file location. So I store my mp3 files in a sub folder in the assets folder called audio. So the playAudio method needs an argument similar to this: "audio/example.mp3". If it was stored directly in the assets folder it would look like this: "example.mp3".

Attaching the Audio Interface to the WebView control

Now, we need to attach the AudioInterface class to the WebView control in the onCreate method in order to make it available for the JavaScript code. So add the following code to the onCreate method we edited earlier in the layout's Java file:

myWebView.addJavascriptInterface(new AudioInterface(this), "AndAud");

Invoking an Audio Interface function from the HTML5 page using JavaScript

Now we can call the playAudio function from JavaScript inside the HTML5 file by using this method:

<script type="text/javascript">
	//AndAud is the alias of the AudioInterface class that we attached to the WebView
	AndAud.playAudio("audio/One.mp3");
</script> 

And that's it, it's kind of an annoying work around but at least you know it will work rather than waiting on the <audio> kinks to be worked out.