MediaPlayer

Class Overview

MediaPlayer class can be used to control playback of audio/video files and streams. An example on how to use the methods in this class can be found in VideoView. Please see Audio and Video for additional help using MediaPlayer.

Topics covered here are:

1. State Diagram
2. Valid and Invalid States
3. Permissions
4. Register informational and error callbacks

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 after release() 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 the Idle 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(FileDescriptor), or setDataSource(String), or setDataSource(Context, Uri), or setDataSource(FileDescriptor, long, long) transfers a MediaPlayer object in the Idle state to the Initialized 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 to prepare() (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 via setOnPreparedListener(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 the Started 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 via setOnBufferingUpdateListener(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 via pause(). 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 the Started 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 via setOnSeekCompleteListener(OnSeekCompleteListener).
  • Please note that seekTo(int) can also be called in the other states, such as Prepared, Paused and PlaybackCompleted 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 the Started 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 via setOnCompletionListener(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.

  Valid and invalid states

  Method Name	Valid Sates	Invalid States	Comments
  attachAuxEffect	{Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Idle, Error}	This method must be called after setDataSource. Calling it does not change the object state.
  getAudioSessionId	any	{}	This method can be called in any state and calling it does not change the object state.
  getCurrentPosition	{Idle, Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  getDuration	{Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Idle, Initialized, Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  getVideoHeight	{Idle, Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  getVideoWidth	{Idle, Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  isPlaying	{Idle, Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted}	{Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  pause	{Started, Paused}	{Idle, Initialized, Prepared, Stopped, PlaybackCompleted, Error}	Successful invoke of this method in a valid state transfers the object to the Paused state. Calling this method in an invalid state transfers the object to the Error state.
  prepare	{Initialized, Stopped}	{Idle, Prepared, Started, Paused, PlaybackCompleted, Error}	Successful invoke of this method in a valid state transfers the object to the Prepared state. Calling this method in an invalid state throws an IllegalStateException.
  prepareAsync	{Initialized, Stopped}	{Idle, Prepared, Started, Paused, PlaybackCompleted, Error}	Successful invoke of this method in a valid state transfers the object to the Preparing state. Calling this method in an invalid state throws an IllegalStateException.
  release	any	{}	After release(), the object is no longer available.
  reset	{Idle, Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted, Error}	{}	After reset(), the object is like being just created.
  seekTo	{Prepared, Started, Paused, PlaybackCompleted}	{Idle, Initialized, Stopped, Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  setAudioSessionId	{Idle}	{Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted, Error}	This method must be called in idle state as the audio session ID must be known before calling setDataSource. Calling it does not change the object state.
  setAudioStreamType	{Idle, Initialized, Stopped, Prepared, Started, Paused, PlaybackCompleted}	{Error}	Successful invoke of this method does not change the state. In order for the target audio stream type to become effective, this method must be called before prepare() or prepareAsync().
  setAuxEffectSendLevel	any	{}	Calling this method does not change the object state.
  setDataSource	{Idle}	{Initialized, Prepared, Started, Paused, Stopped, PlaybackCompleted, Error}	Successful invoke of this method in a valid state transfers the object to the Initialized state. Calling this method in an invalid state throws an IllegalStateException.
  setDisplay	any	{}	This method can be called in any state and calling it does not change the object state.
  setSurface	any	{}	This method can be called in any state and calling it does not change the object state.
  setLooping	{Idle, Initialized, Stopped, Prepared, Started, Paused, PlaybackCompleted}	{Error}	Successful invoke of this method in a valid state does not change the state. Calling this method in an invalid state transfers the object to the Error state.
  isLooping	any	{}	This method can be called in any state and calling it does not change the object state.
  setOnBufferingUpdateListener	any	{}	This method can be called in any state and calling it does not change the object state.
  setOnCompletionListener	any	{}	This method can be called in any state and calling it does not change the object state.
  setOnErrorListener	any	{}	This method can be called in any state and calling it does not change the object state.
  setOnPreparedListener	any	{}	This method can be called in any state and calling it does not change the object state.
  setOnSeekCompleteListener	any	{}	This method can be called in any state and calling it does not change the object state.
  setScreenOnWhilePlaying	any	{}	This method can be called in any state and calling it does not change the object state.
  setVolume	{Idle, Initialized, Stopped, Prepared, Started, Paused, PlaybackCompleted}	{Error}	Successful invoke of this method does not change the state.
  setWakeMode	any	{}	This method can be called in any state and calling it does not change the object state.
  start	{Prepared, Started, Paused, PlaybackCompleted}	{Idle, Initialized, Stopped, Error}	Successful invoke of this method in a valid state transfers the object to the Started state. Calling this method in an invalid state transfers the object to the Error state.
  stop	{Prepared, Started, Stopped, Paused, PlaybackCompleted}	{Idle, Initialized, Error}	Successful invoke of this method in a valid state transfers the object to the Stopped state. Calling this method in an invalid state transfers the object to the Error state.

  Permissions

  One may need to declare a corresponding WAKE_LOCK permission <uses-permission> element.

  This class requires the INTERNET permission when used with network-based content.

  Callbacks

  Applications may want to register for informational and error events in order to be informed of some internal state update and possible runtime errors during playback or streaming. Registration for these events is done by properly setting the appropriate listeners (via calls to setOnPreparedListener(OnPreparedListener)setOnPreparedListener, setOnVideoSizeChangedListener(OnVideoSizeChangedListener)setOnVideoSizeChangedListener, setOnSeekCompleteListener(OnSeekCompleteListener)setOnSeekCompleteListener, setOnCompletionListener(OnCompletionListener)setOnCompletionListener, setOnBufferingUpdateListener(OnBufferingUpdateListener)setOnBufferingUpdateListener, setOnInfoListener(OnInfoListener)setOnInfoListener, setOnErrorListener(OnErrorListener)setOnErrorListener, etc). In order to receive the respective callback associated with these listeners, applications are required to create MediaPlayer objects on a thread with its own Looper running (main UI thread by default has a Looper running).

Summary

[Expand] Inherited Methods

From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.