MediaPlayer experiments

When working with the media player there are some little things I have found that you need to keep an eye out for. The first is that the MediaPlayer object is quite happy to continue playing your media track after you have closed the app itself. This is an example of how important it is to release all resources and to monitor which ones persist in the memory of the device! While bumming around on the android developer website, I started looking into the billing API and found another example in the Google Payments "Binding" when an in-app purchase is attempted. When an app closes, if that binding is not released, it can use up system resources and degrade performance.

My experiments with the media player began with finding a question on the learnandroid subreddit, which asked about pausing media with a touchevent. From my reading I could see that the poster had not prepared the media track after stopping it, something which is unique to that circumstance but not the pause method. The poster also had a bit of confusion about the touch event itself and where to trigger the media playing. After posting a quick suggestion I decided that I should try to implement a music player in a test app too to get to grips with the little things that might be confusing for a beginner.

Following on from my blank screen SurfaceView test, I used VLC to convert a ripped mp3 into the OGGVorbis format with reduced sound quality (to save on memory) and added that into a new assets folder. From my previous experiemnts with Soundpool (An app with pikachu on it that says pikachu when you touch the screen, and plays a computer booting up sfx from pokemon firered on launch), I knew that sound files can be retrieved using the AssetManager in android. I made the first mistake in not putting the new directory in the right place in the file structure, but that didn't become apparent until it was fully set up.

My first set up was to have all of the media player implemented in the SurfaceView class itself, which is a Runnable in a class called Screen. The implementation included instantiating an asset manager, trying to get the file i wanted an AssetFileDescriptor which I could pass into a new instance of MediaPlayer. The process itself was all set up and the data source set and media started, but the app itself didn't work. After adding some Log notes and an exception message for the try-catch block I found that the asset manager wasn't retrieving the files in the folder, and looked back to my original pikachu app to find the structure difference. 

Once the file was able to load and play I ran the app and lo and behold, the music played, (Nine Inchnails- Satellites for those who need to know!). I was elated, then I closed the app and hmm.. still music.
I knew this had something to do with releasing the resources and the activity life cycle so I started to look there for ways to control my music. I started with onStop, onPause and onResume methods inside my SurfaceView which were called from the main activity, and implemented checks for if the media player was valid and playing etc, and stopped the music and restarted it as I expected. This did not work. The app was happy enough to stop the music but not to restart it when the app was loaded up again. I understood that the app was saved in temporary memory when the app was minimized or obscured, so the app was going through the onPause method, but I didn't realize the onStop method was being called also!

Going back I was able to debug my app and place appropriate boolean flags to control the music playing. In the onPause method, the music is (if it is not already) paused, and on resume the music is (if not null such as on initial bootup of the app) started again. The call to onStop was moved into an if block which checked that the app was not being closed fully (isFinishing()) and if so, stopped playback and also released the media player.
With my experiment finally performing the way I wanted it to, I was finally able to begin abstracting the audio into a seperate class. I created an Audio class that could handle music using static methods, which would mean it is accessible throughout my app. Instead of using a default constructor to set up the Audio environment, I opted instead to use static methods that only initialize variables if they are going to be used. I currently have a method that is needed to pass in a context for use in attaining the assets, but later on I will access this statically from a core class that handles the game.

The Audio class also has onPause, onResume and onStop methods which can be called to ensure that any active media, be it sound FX from the soundPool or music from MediaPlayer are paused and resumed correctly, and destroyed on closing the app.

I am really quite happy with the progress I am making in understanding these (albeit simple) aspects of app development. I want to be able to say not only that I understand the theory, but that I can put code on paper to describe the processes and show that I understand the way these systems work together on a more holistic level.

The code for my Audio and Screen app are linked below for viewing.

MainActivity Class
Audio Class
SurfaceView Class

Return to Game Development

Recently I have moved away from the Udacity course and tried to get back on track with the game development that I have wanted to do all along. I have returned my studies to Beginning Android Games, an Apress book I got a while back. When I first started trying to learn from this book I found the information to be far too heavy, I was not experienced enough with the Android OS to get it. Now that I have a better understanding, the pieces are coming together much easier.

While working through the examples, I have been playing around with the code and finding out the OTHER methods that some of the classes do. While I had made a game on Android following a "For Dummies" book in the past, this time I actually understand the process, the effect that the Activity Life Cycle has, and can see where the ideas I have fit into the code.

To help me keep notes and have an "in my own words" reference, I have been typing up  notes into Google Keep, an app I have had on my phone for a long time and rarely used. Being able to type quickly has always prevented me from note-taking on my phone. I am a terrible touch screen typist! Using the in-browser version of Google Keep has been a lifesaver- actual keyboard typing, and sync to my phone for on the go note revision. I have found myself memorizing key concepts quicker with these notes, and can now comfortably say that an extremely basic framework in a regular View can flow pretty quickly from my fingers. I do enjoy making notes and even updating them to make them more precise, but I can't always be at my laptop- for this reason I have contemplated buying a bluetooth for a while. (I have planned to buy a tablet for myself for quite a while now and really wanted a keyboard for it- so I have been watching Amazon and Bestbuy for a deal daily!) I finally ordered myself a keyboard last night, and hopefully that gives me more opportunities to be productive- either in writing up ideas, taking notes or coding when I am not limited by the amount of time I can comfortably sit at the computer.

As an example of the notes I have been keeping, here is my first entry!

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Soundpool is a RAM based storage for small soundFX files, ideally in .ogg format and shorter than about 5 seconds. Setting up a SoundPool requires the parameters indicating how many sounds can play simultaneously (20 is a good default), which sound stream is being used (AudioManager.STREAM_MUSIC for media of any type), and a final unused parameter, default 0.

SoundPool sp = new SoundPool(20, AudioManager.STREAM_MUSIC, 0);
The SoundPool default constructor has been deprecated with the release of Lollipop, and now utilises a Builder for instantiating a SoundPool object.

SoundPool sp = SoundPool.Builder()  
.setUsage(audioAttributes)  
.setStream()  
.build();

 To load a soundFX file to the Pool, you have to get an AssetFileDescriptor from the Asset file.

AssetManager assetManager = context.getAssets();
AssetFileDescriptor asset1 = assetManager.openFD("dir/filename.extension");

When adding the descriptor to the soundpool, it will return an integer which identifies the sound loaded, which can be used as a parameter later. It is vital therefore that any files loaded be done so in an integer expression. the load method itself will take in the AssetFileDescriptor and a sound priority int as parameters. The sound priority is currently unused as is default as 1 (similar I guess to the weight attribute in xml layouts, having them all at 1 gives uniform importance).

int asset1IdNum = sp.load(asset1, 1);

This asset can later be played using the SoundPool instance, by referencing the identifier for the resource, as well as some other parameters.

sp.play(identifierInt, float leftChannelVolume, float rightChannelVolume, int priority, int looping, float playbackSpeed)

The channelVolume parameters allow a sound to be set on one ear or the other. The priority again is unused and is defaulted to 0. Looping is often not a good idea for a sound effect and is thus set to 0, and playback speed will be 1 by default, less for slow play and more for fast playback.
When all use of the SoundPool is done, it is best practice to release the resources directly by using either specific calls to soundPool.unload(identifierInt) or to all resources using soundPool.release();

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I have made notes on MusicStream, working with the View and onDraw() method (invalidating as a method of continuous graphics rendering), setting the application to keep the screen on, go fullscreen and hide the notification bar and working in SurfaceView and Threads.

I'm hoping that my notes will not only enable me to retain information better, but also that they may help me to guide others if they ask me for advice on starting on a similar path!

There are notes I have to include after todays coding to describe how to set a listener for loading files, as I wanted to have a specific sound effect play as my testing app opens (computer booting up sound effect from a monster catching game you may have heard of!)

Update to R2-D2 print

Now with second layer for black. The registration I used worked out really well. The first attempt at a second layer that I did last time I was printing didn't line up well at all and I was super worried, luckily it worked out!