Mediaplayer State Diagram

State Diagram

Playback control of audio/video files and streams is managed as a state machine. The following diagram shows the life cycle and the states of a MediaPlayer object driven by the supported playback control operations. The ovals represent the states a MediaPlayer object may reside in. The arcs represent the playback control operations that drive the object state transition. There are two types of arcs. The arcs with a single arrow head represent synchronous method calls, while those with a double arrow head represent asynchronous method calls.

From this state diagram, one can see that a MediaPlayer object has the following states:

• When a MediaPlayer object is just created using new or after reset() is called, it is in the Idle state; and afterrelease() is called, it is in the End state. Between these two states is the life cycle of the MediaPlayer object.
  • There is a subtle but important difference between a newly constructed MediaPlayer object and the MediaPlayer object after reset() is called. It is a programming error to invoke methods such as getCurrentPosition(),getDuration(), getVideoHeight(), getVideoWidth(), setAudioStreamType(int), setLooping(boolean),setVolume(float,float), pause(), start(), stop(), seekTo(int), prepare() or prepareAsync() in theIdle state for both cases. If any of these methods is called right after a MediaPlayer object is constructed, the user supplied callback method OnErrorListener.onError() won't be called by the internal player engine and the object state remains unchanged; but if these methods are called right after reset(), the user supplied callback method OnErrorListener.onError() will be invoked by the internal player engine and the object will be transfered to the Error state.
  • It is also recommended that once a MediaPlayer object is no longer being used, call release() immediately so that resources used by the internal player engine associated with the MediaPlayer object can be released immediately. Resource may include singleton resources such as hardware acceleration components and failure to call release() may cause subsequent instances of MediaPlayer objects to fallback to software implementations or fail altogether. Once the MediaPlayer object is in the End state, it can no longer be used and there is no way to bring it back to any other state.
  • Furthermore, the MediaPlayer objects created using new is in the Idle state, while those created with one of the overloaded convenient create methods are NOT in the Idle state. In fact, the objects are in the Prepared state if the creation using create method is successful.
• In general, some playback control operation may fail due to various reasons, such as unsupported audio/video format, poorly interleaved audio/video, resolution too high, streaming timeout, and the like. Thus, error reporting and recovery is an important concern under these circumstances. Sometimes, due to programming errors, invoking a playback control operation in an invalid state may also occur. Under all these error conditions, the internal player engine invokes a user supplied OnErrorListener.onError() method if an OnErrorListener has been registered beforehand via setOnErrorListener(android.media.MediaPlayer.OnErrorListener).
  • It is important to note that once an error occurs, the MediaPlayer object enters the Error state (except as noted above), even if an error listener has not been registered by the application.
  • In order to reuse a MediaPlayer object that is in the Error state and recover from the error, reset() can be called to restore the object to its Idle state.
  • It is good programming practice to have your application register a OnErrorListener to look out for error notifications from the internal player engine.
  • IllegalStateException is thrown to prevent programming errors such as calling prepare(), prepareAsync(), or one of the overloaded setDataSource methods in an invalid state.
• Calling setDataSource(java.io.FileDescriptor), or setDataSource(java.lang.String), orsetDataSource(android.content.Context,android.net.Uri), orsetDataSource(java.io.FileDescriptor,long,long) transfers a MediaPlayer object in the Idle state to theInitialized state.
  • An IllegalStateException is thrown if setDataSource() is called in any other state.
  • It is good programming practice to always look out for IllegalArgumentException and IOException that may be thrown from the overloaded setDataSource methods.
• A MediaPlayer object must first enter the Prepared state before playback can be started.
  • There are two ways (synchronous vs. asynchronous) that the Prepared state can be reached: either a call toprepare() (synchronous) which transfers the object to the Prepared state once the method call returns, or a call to prepareAsync() (asynchronous) which first transfers the object to the Preparing state after the call returns (which occurs almost right way) while the internal player engine continues working on the rest of preparation work until the preparation work completes. When the preparation completes or when prepare() call returns, the internal player engine then calls a user supplied callback method, onPrepared() of the OnPreparedListener interface, if an OnPreparedListener is registered beforehand viasetOnPreparedListener(android.media.MediaPlayer.OnPreparedListener).
  • It is important to note that the Preparing state is a transient state, and the behavior of calling any method with side effect while a MediaPlayer object is in the Preparing state is undefined.
  • An IllegalStateException is thrown if prepare() or prepareAsync() is called in any other state.
  • While in the Prepared state, properties such as audio/sound volume, screenOnWhilePlaying, looping can be adjusted by invoking the corresponding set methods.
• To start the playback, start() must be called. After start() returns successfully, the MediaPlayer object is in theStarted state. isPlaying() can be called to test whether the MediaPlayer object is in the Started state.
  • While in the Started state, the internal player engine calls a user supplied OnBufferingUpdateListener.onBufferingUpdate() callback method if a OnBufferingUpdateListener has been registered beforehand viasetOnBufferingUpdateListener(android.media.MediaPlayer.OnBufferingUpdateListener). This callback allows applications to keep track of the buffering status while streaming audio/video.
  • Calling start() has not effect on a MediaPlayer object that is already in the Started state.
• Playback can be paused and stopped, and the current playback position can be adjusted. Playback can be paused viapause(). When the call to pause() returns, the MediaPlayer object enters the Paused state. Note that the transition from the Started state to the Paused state and vice versa happens asynchronously in the player engine. It may take some time before the state is updated in calls to isPlaying(), and it can be a number of seconds in the case of streamed content.
  • Calling start() to resume playback for a paused MediaPlayer object, and the resumed playback position is the same as where it was paused. When the call to start() returns, the paused MediaPlayer object goes back to theStarted state.
  • Calling pause() has no effect on a MediaPlayer object that is already in the Paused state.
• Calling stop() stops playback and causes a MediaPlayer in the Started, Paused, Prepared or PlaybackCompleted state to enter the Stopped state.
  • Once in the Stopped state, playback cannot be started until prepare() or prepareAsync() are called to set the MediaPlayer object to the Prepared state again.
  • Calling stop() has no effect on a MediaPlayer object that is already in the Stopped state.
• The playback position can be adjusted with a call to seekTo(int).
  • Although the asynchronuous seekTo(int) call returns right way, the actual seek operation may take a while to finish, especially for audio/video being streamed. When the actual seek operation completes, the internal player engine calls a user supplied OnSeekComplete.onSeekComplete() if an OnSeekCompleteListener has been registered beforehand viasetOnSeekCompleteListener(android.media.MediaPlayer.OnSeekCompleteListener).
  • Please note that seekTo(int) can also be called in the other states, such as Prepared, Paused andPlaybackCompleted state.
  • Furthermore, the actual current playback position can be retrieved with a call to getCurrentPosition(), which is helpful for applications such as a Music player that need to keep track of the playback progress.
• When the playback reaches the end of stream, the playback completes.
  • If the looping mode was being set to truewith setLooping(boolean), the MediaPlayer object shall remain in theStarted state.
  • If the looping mode was set to false , the player engine calls a user supplied callback method, OnCompletion.onCompletion(), if a OnCompletionListener is registered beforehand viasetOnCompletionListener(android.media.MediaPlayer.OnCompletionListener). The invoke of the callback signals that the object is now in the PlaybackCompleted state.
  • While in the PlaybackCompleted state, calling start() can restart the playback from the beginning of the audio/video source.