# Analytics

ExoPlayer supports a wide range of playback analytics needs. Ultimately, analytics is about collecting, interpreting, aggregating and summarizing data from playbacks. This data can be used either on the device, for example for logging, debugging, or to inform future playback decisions, or reported to a server to monitor playbacks across all devices.

An analytics system usually needs to collect events first, and then process them further to make them meaningful:

• Event collection: This can be done by registering an AnalyticsListener on an ExoPlayer instance. Registered analytics listeners receive events as they occur during usage of the player. Each event is associated with the corresponding media item in the playlist, as well as playback position and timestamp metadata.
• Event processing: Some analytics systems upload raw events to a server, with all event processing performed server-side. It’s also possible to process events on the device, and doing so may be simpler or reduce the amount of information that needs to be uploaded. ExoPlayer provides PlaybackStatsListener, which allows you to perform the following processing steps:
1. Event interpretation: To be useful for analytics purposes, events need to be interpreted in the context of a single playback. For example the raw event of a player state change to STATE_BUFFERING may correspond to initial buffering, a rebuffer, or buffering that happens after a seek.
2. State tracking: This step converts events to counters. For example, state change events can be converted to counters tracking how much time is spent in each playback state. The result is a basic set of analytics data values for a single playback.
3. Aggregation: This step combines the analytics data across multiple playbacks, typically by adding up counters.
4. Calculation of summary metrics: Many of the most useful metrics are those that compute averages or combine the basic analytics data values in other ways. Summary metrics can be calculated for single or multiple playbacks.

## Event collection with AnalyticsListener

Raw playback events from the player are reported to AnalyticsListener implementations. You can easily add your own listener and override only the methods you are interested in:

@Override
public void onPlaybackStateChanged(
EventTime eventTime, @Player.State int state) {
}

@Override
public void onDroppedVideoFrames(
EventTime eventTime, int droppedFrames, long elapsedMs) {
}
});

The EventTime that’s passed to each callback associates the event to a media item in the playlist, as well as playback position and timestamp metadata:

• realtimeMs: The wall clock time of the event.
• timeline, windowIndex and mediaPeriodId: Defines the playlist and the item within the playlist to which the event belongs. The mediaPeriodId contains optional additional information, for example indicating whether the event belongs to an ad within the item.
• eventPlaybackPositionMs: The playback position in the item when the event occurred.
• currentTimeline, currentWindowIndex, currentMediaPeriodId and currentPlaybackPositionMs: As above but for the currently playing item. The currently playing item may be different from the item to which the event belongs, for example if the event corresponds to pre-buffering of the next item to be played.

## Event processing with PlaybackStatsListener

PlaybackStatsListener is an AnalyticsListener that implements on device event processing. It calculates PlaybackStats, with counters and derived metrics including:

• Summary metrics, for example the total playback time.
• Adaptive playback quality metrics, for example the average video resolution.
• Rendering quality metrics, for example the rate of dropped frames.
• Resource usage metrics, for example the number of bytes read over the network.

You will find a complete list of the available counts and derived metrics in the PlaybackStats Javadoc.

PlaybackStatsListener calculates separate PlaybackStats for each media item in the playlist, and also each client-side ad inserted within these items. You can provide a callback to PlaybackStatsListener to be informed about finished playbacks, and use the EventTime passed to the callback to identify which playback finished. It’s possible to aggregate the analytics data for multiple playbacks. It’s also possible to query the PlaybackStats for the current playback session at any time using PlaybackStatsListener.getPlaybackStats().

new PlaybackStatsListener(
/* keepHistory= */ true, (eventTime, playbackStats) -> {
// Analytics data for the session started at eventTime is ready.
}));

The constructor of PlaybackStatsListener gives the option to keep the full history of processed events. Note that this may incur an unknown memory overhead depending on the length of the playback and the number of events. Therefore you should only turn it on if you need access to the full history of processed events, rather than just to the final analytics data.

Note that PlaybackStats uses an extended set of states to indicate not only the state of the media, but also the user intention to play and more detailed information such as why playback was interrupted or ended:

Playback state User intention to play No intention to play
Before playback JOINING_FOREGROUND NOT_STARTED, JOINING_BACKGROUND
Active playback PLAYING
Interrupted playback BUFFERING, SEEKING PAUSED, PAUSED_BUFFERING, SUPPRESSED, SUPPRESSED_BUFFERING, INTERRUPTED_BY_AD
End states   ENDED, STOPPED, FAILED, ABANDONED

The user intention to play is important to distinguish times when the user was actively waiting for playback to continue from passive wait times. For example, PlaybackStats.getTotalWaitTimeMs returns the total time spent in the JOINING_FOREGROUND, BUFFERING and SEEKING states, but not the time when playback was paused. Similarly, PlaybackStats.getTotalPlayAndWaitTimeMs will return the total time with a user intention to play, that is the total active wait time and the total time spent in the PLAYING state.

### Processed and interpreted events

You can record processed and interpreted events by using PlaybackStatsListener with keepHistory=true. The resulting PlaybackStats will contain the following event lists:

• playbackStateHistory: An ordered list of extended playback states with the EventTime at which they started to apply. You can also use PlaybackStats.getPlaybackStateAtTime to look up the state at a given wall clock time.
• mediaTimeHistory: A history of wall clock time and media time pairs allowing you to reconstruct which parts of the media were played at which time. You can also use PlaybackStats.getMediaTimeMsAtRealtimeMs to look up the playback position at a given wall clock time.
• videoFormatHistory and audioFormatHistory: Ordered lists of video and audio formats used during playback with the EventTime at which they started to be used.
• fatalErrorHistory and nonFatalErrorHistory: Ordered lists of fatal and non-fatal errors with the EventTime at which they occurred. Fatal errors are those that ended playback, whereas non-fatal errors may have been recoverable.

### Single-playback analytics data

This data is automatically collected if you use PlaybackStatsListener, even with keepHistory=false. The final values are the public fields that you can find in the PlaybackStats Javadoc and the playback state durations returned by getPlaybackStateDurationMs. For convenience, you’ll also find methods like getTotalPlayTimeMs and getTotalWaitTimeMs that return the duration of specific playback state combinations.

Log.d("DEBUG", "Playback summary: "
+ "play time = " + playbackStats.getTotalPlayTimeMs()
+ ", rebuffers = " + playbackStats.totalRebufferCount);

Some values like totalVideoFormatHeightTimeProduct are only useful when calculating derived summary metrics like the average video height, but are required to correctly combine multiple PlaybackStats together.

### Aggregate analytics data of multiple playbacks

You can combine multiple PlaybackStats together by calling PlaybackStats.merge. The resulting PlaybackStats will contain the aggregated data of all merged playbacks. Note that it won’t contain the history of individual playback events, since these cannot be aggregated.

PlaybackStatsListener.getCombinedPlaybackStats can be used to get an aggregated view of all analytics data collected in the lifetime of a PlaybackStatsListener.

### Calculated summary metrics

In addition to the basic analytics data, PlaybackStats provides many methods to calculate summary metrics.

Log.d("DEBUG", "Additional calculated summary metrics: "
+ "average video bitrate = " + playbackStats.getMeanVideoFormatBitrate()
+ ", mean time between rebuffers = "
+ playbackStats.getMeanTimeBetweenRebuffers());

### Associating analytics data with playback metadata

When collecting analytics data for individual playbacks, you may wish to associate the playback analytics data with metadata about the media being played.

It’s advisable to set media-specific metadata with MediaItem.Builder.setTag. The media tag is part of the EventTime reported for raw events and when PlaybackStats are finished, so it can be easily retrieved when handling the corresponding analytics data:

new PlaybackStatsListener(
/* keepHistory= */ false, (eventTime, playbackStats) -> {
Object mediaTag =
eventTime.timeline.getWindow(eventTime.windowIndex, new Window())
.mediaItem.localConfiguration.tag;
// Report playbackStats with mediaTag metadata.
});

### Reporting custom analytics events

In case you need to add custom events to the analytics data, you need to save these events in your own data structure and combine them with the reported PlaybackStats later. If it helps, you can extend DefaultAnalyticsCollector to be able to generate EventTime instances for your custom events and send them to the already registered listeners as shown in the following example.

interface ExtendedListener extends AnalyticsListener {
void onCustomEvent(EventTime eventTime);
}

class ExtendedCollector extends DefaultAnalyticsCollector {
public void customEvent() {
EventTime eventTime = generateCurrentPlayerMediaPeriodEventTime();
sendEvent(eventTime, CUSTOM_EVENT_ID, listener -> {
if (listener instanceof ExtendedListener) {
((ExtendedListener) listener).onCustomEvent(eventTime);
}
});
}
}

// Usage - Setup and listener registration.
ExoPlayer player = new ExoPlayer.Builder(context)
.setAnalyticsCollector(new ExtendedCollector())
.build();