推动历史发展的不是法律，而是金钱. —— JP摩根
1. 应用场景视频播放要循环播放，另外要在视频第一遍播放结束时出现某种提示。
循环播放：我们可以通过设置setRepeatMode() 进行设置。另外在Player.EventListener的onPlaybackStateChanged(int state) 对播放过程进行监听。
具体过程如下：
public void onPlaybackStateChanged(int state) { Log.d(TAG, "onPlaybackStateChanged 播放状态：" + state); switch (state) { case Player.STATE_READY: Log.d(TAG, "加载就绪，可以播放"); ... break; case Player.STATE_BUFFERING: Log.d(TAG, "缓冲中..."); ... break; case Player.STATE_ENDED: Log.d(TAG, "播放结束..."); ... break; case Player.STATE_IDLE: ... break; } }一切看起来都是那么的完美…
2. 问题重点来袭：Player.STATE_ENDED 在开启循环模式下是不会被触发的。
静下来想一下，不难理解，这个状态：表示播放器结束播放媒体。(PS: 循环模式当然是不会结束的啦…)
难道我们只能采取QAQ的方式(关闭循环模式然后在播放结束的时候重新播放…)。如果是这样做的话，费时费力暂且不谈，那还需要我在这里BB，那人生还有什么意趣儿？
3. 解决方案 public void onPositionDiscontinuity(@Player.DiscontinuityReason int reason) { if(reason == DISCONTINUITY_REASON_PERIOD_TRANSITION){ // TODO... } }请自行翻译：
/** * Automatic playback transition from one period in the timeline to the next. The period index may * be the same as it was before the discontinuity in case the current period is repeated. */ int DISCONTINUITY_REASON_PERIOD_TRANSITION = 0; 4. 原理其本质跟QAQ方案是有着异曲同工之妙。
根据timeline(时间轴)的变化，来调用onPositionDiscontinuity()。【PS： 循环播放他也是 0 ----> 终点 ，0 ----> 终点,…进行循环的】
没什么好解释的，请直接看代码注释：
/** * Listener of changes in player state. All methods have no-op default implementations to allow * selective overrides. */ interface EventListener { /** * Called when the timeline has been refreshed. * * <p>Note that if the timeline has changed then a position discontinuity may also have * occurred. For example, the current period index may have changed as a result of periods being * added or removed from the timeline. This will <em>not</em> be reported via a separate call to * {@link #onPositionDiscontinuity(int)}. * * @param timeline The latest timeline. Never null, but may be empty. * @param reason The {@link TimelineChangeReason} responsible for this timeline change. */ @SuppressWarnings("deprecation") default void onTimelineChanged(Timeline timeline, @TimelineChangeReason int reason) { Object manifest = null; if (timeline.getWindowCount() == 1) { // Legacy behavior was to report the manifest for single window timelines only. Timeline.Window window = new Timeline.Window(); manifest = timeline.getWindow(0, window).manifest; } // Call deprecated version. onTimelineChanged(timeline, manifest, reason); }...}附上参考链接：ExoPlayer STATE_ENDED not called after song is finished
最后废话一句，对ExoPlayer不了解的朋友，可以参考：ExoPlayer-Study点滴