com.google.android.exoplayer2.trackselection

Class TrackSelector

java.lang.Object

com.google.android.exoplayer2.trackselection.TrackSelector

Direct Known Subclasses:

MappingTrackSelector

public abstract class TrackSelector
extends java.lang.Object

The component of an ExoPlayer responsible for selecting tracks to be consumed by each of the player's Renderers. The DefaultTrackSelector implementation should be suitable for most use cases.

Interactions with the player

The following interactions occur between the player and its track selector during playback.

• When the player is created it will initialize the track selector by calling init(InvalidationListener, BandwidthMeter).
• When the player needs to make a track selection it will call selectTracks(RendererCapabilities[], TrackGroupArray). This typically occurs at the start of playback, when the player starts to buffer a new period of the media being played, and when the track selector invalidates its previous selections.
• The player may perform a track selection well in advance of the selected tracks becoming active, where active is defined to mean that the renderers are actually consuming media corresponding to the selection that was made. For example when playing media containing multiple periods, the track selection for a period is made when the player starts to buffer that period. Hence if the player's buffering policy is to maintain a 30 second buffer, the selection will occur approximately 30 seconds in advance of it becoming active. In fact the selection may never become active, for example if the user seeks to some other period of the media during the 30 second gap. The player indicates to the track selector when a selection it has previously made becomes active by calling onSelectionActivated(Object).
• If the track selector wishes to indicate to the player that selections it has previously made are invalid, it can do so by calling TrackSelector.InvalidationListener.onTrackSelectionsInvalidated() on the TrackSelector.InvalidationListener that was passed to init(InvalidationListener, BandwidthMeter). A track selector may wish to do this if its configuration has changed, for example if it now wishes to prefer audio tracks in a particular language. This will trigger the player to make new track selections. Note that the player will have to re-buffer in the case that the new track selection for the currently playing period differs from the one that was invalidated.

Renderer configuration

The TrackSelectorResult returned by selectTracks(RendererCapabilities[], TrackGroupArray) contains not only TrackSelections for each renderer, but also RendererConfigurations defining configuration parameters that the renderers should apply when consuming the corresponding media. Whilst it may seem counter-intuitive for a track selector to also specify renderer configuration information, in practice the two are tightly bound together. It may only be possible to play a certain combination tracks if the renderers are configured in a particular way. Equally, it may only be possible to configure renderers in a particular way if certain tracks are selected. Hence it makes sense to determined the track selection and corresponding renderer configurations in a single step.

Threading model

All calls made by the player into the track selector are on the player's internal playback thread. The track selector may call TrackSelector.InvalidationListener.onTrackSelectionsInvalidated() from any thread.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	TrackSelector.InvalidationListener Notified when selections previously made by a TrackSelector are no longer valid.

Constructor Summary

Constructors

Constructor and Description
TrackSelector()

Method Summary

Modifier and Type	Method and Description
protected BandwidthMeter	getBandwidthMeter() Returns a bandwidth meter which can be used by track selections to select tracks.
void	init(TrackSelector.InvalidationListener listener, BandwidthMeter bandwidthMeter) Called by the player to initialize the selector.
protected void	invalidate() Calls TrackSelector.InvalidationListener.onTrackSelectionsInvalidated() to invalidate all previously generated track selections.
abstract void	onSelectionActivated(java.lang.Object info) Called by the player when a TrackSelectorResult previously generated by selectTracks(RendererCapabilities[], TrackGroupArray) is activated.
abstract TrackSelectorResult	selectTracks(RendererCapabilities[] rendererCapabilities, TrackGroupArray trackGroups) Called by the player to perform a track selection.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TrackSelector

public TrackSelector()

Method Detail

init

public final void init(TrackSelector.InvalidationListener listener,
                       BandwidthMeter bandwidthMeter)

Called by the player to initialize the selector.

Parameters:

listener - An invalidation listener that the selector can call to indicate that selections it has previously made are no longer valid.

bandwidthMeter - A bandwidth meter which can be used by track selections to select tracks.

selectTracks

public abstract TrackSelectorResult selectTracks(RendererCapabilities[] rendererCapabilities,
                                                 TrackGroupArray trackGroups)
                                          throws ExoPlaybackException

Called by the player to perform a track selection.

Parameters:

rendererCapabilities - The RendererCapabilities of the renderers for which tracks are to be selected.

trackGroups - The available track groups.

Returns:

A TrackSelectorResult describing the track selections.

Throws:

ExoPlaybackException - If an error occurs selecting tracks.

onSelectionActivated

public abstract void onSelectionActivated(java.lang.Object info)

Called by the player when a TrackSelectorResult previously generated by selectTracks(RendererCapabilities[], TrackGroupArray) is activated.

Parameters:

info - The value of TrackSelectorResult.info in the activated selection.

invalidate

protected final void invalidate()

Calls TrackSelector.InvalidationListener.onTrackSelectionsInvalidated() to invalidate all previously generated track selections.

getBandwidthMeter

protected final BandwidthMeter getBandwidthMeter()

Returns a bandwidth meter which can be used by track selections to select tracks. Must only be called after init(InvalidationListener, BandwidthMeter) has been called.