import com.google.android.exoplayer.util.SystemClock; //导入依赖的package包/类
@Override
public void continueBuffering(long playbackPositionUs) {
  if (manifestFetcher == null || !currentManifest.dynamic || fatalError != null) {
    return;
  }

  MediaPresentationDescription newManifest = manifestFetcher.getManifest();
  if (newManifest != null && newManifest != processedManifest) {
    processManifest(newManifest);
    // Manifests may be rejected, so the new manifest may not become the next currentManifest.
    // Track a manifest has been processed to avoid processing twice when it was discarded.
    processedManifest = newManifest;
  }

  // TODO: This is a temporary hack to avoid constantly refreshing the MPD in cases where
  // minUpdatePeriod is set to 0. In such cases we shouldn't refresh unless there is explicit
  // signaling in the stream, according to:
  // http://azure.microsoft.com/blog/2014/09/13/dash-live-streaming-with-azure-media-service/
  long minUpdatePeriod = currentManifest.minUpdatePeriod;
  if (minUpdatePeriod == 0) {
    minUpdatePeriod = 5000;
  }

  if (android.os.SystemClock.elapsedRealtime()
      > manifestFetcher.getManifestLoadStartTimestamp() + minUpdatePeriod) {
    manifestFetcher.requestRefresh();
  }
}
 

import com.google.android.exoplayer.util.SystemClock; //导入依赖的package包/类
public DefaultBandwidthMeter(Handler eventHandler, EventListener eventListener) {
  this(eventHandler, eventListener, new SystemClock());
}
 

import com.google.android.exoplayer.util.SystemClock; //导入依赖的package包/类
public LimitedBandwidthMeter(Handler eventHandler, EventListener eventListener, int maxWeight) {
    this(eventHandler, eventListener, new SystemClock(), maxWeight);
}
 

import com.google.android.exoplayer.util.SystemClock; //导入依赖的package包/类
/**
 * Constructor to use for live streaming.
 * <p>
 * May also be used for fixed duration content, in which case the call is equivalent to calling
 * the other constructor, passing {@code manifestFetcher.getManifest()} is the first argument.
 *
 * @param manifestFetcher A fetcher for the manifest, which must have already successfully
 *     completed an initial load.
 * @param adaptationSetIndex The index of the adaptation set that should be used.
 * @param representationIndices The indices of the representations within the adaptations set
 *     that should be used. May be null if all representations within the adaptation set should
 *     be considered.
 * @param dataSource A {@link DataSource} suitable for loading the media data.
 * @param formatEvaluator Selects from the available formats.
 * @param liveEdgeLatencyMs For live streams, the number of milliseconds that the playback should
 *     lag behind the "live edge" (i.e. the end of the most recently defined media in the
 *     manifest). Choosing a small value will minimize latency introduced by the player, however
 *     note that the value sets an upper bound on the length of media that the player can buffer.
 *     Hence a small value may increase the probability of rebuffering and playback failures.
 * @param elapsedRealtimeOffsetMs If known, an estimate of the instantaneous difference between
 *     server-side unix time and {@link SystemClock#elapsedRealtime()} in milliseconds, specified
 *     as the server's unix time minus the local elapsed time. It unknown, set to 0.
 * @param eventHandler A handler to use when delivering events to {@code EventListener}. May be
 *     null if delivery of events is not required.
 * @param eventListener A listener of events. May be null if delivery of events is not required.
 */
public DashChunkSource(ManifestFetcher<MediaPresentationDescription> manifestFetcher,
    int adaptationSetIndex, int[] representationIndices, DataSource dataSource,
    FormatEvaluator formatEvaluator, long liveEdgeLatencyMs, long elapsedRealtimeOffsetMs,
    Handler eventHandler, EventListener eventListener) {
  this(manifestFetcher, manifestFetcher.getManifest(), adaptationSetIndex, representationIndices,
      dataSource, formatEvaluator, new SystemClock(), liveEdgeLatencyMs * 1000,
      elapsedRealtimeOffsetMs * 1000, true, eventHandler, eventListener);
}
 

import com.google.android.exoplayer.util.SystemClock; //导入依赖的package包/类
/**
 * Constructor to use for live streaming.
 * <p>
 * May also be used for fixed duration content, in which case the call is equivalent to calling
 * the other constructor, passing {@code manifestFetcher.getManifest()} is the first argument.
 *
 * @param manifestFetcher A fetcher for the manifest, which must have already successfully
 *     completed an initial load.
 * @param trackSelector Selects tracks from manifest periods to be exposed by this source.
 * @param dataSource A {@link DataSource} suitable for loading the media data.
 * @param adaptiveFormatEvaluator For adaptive tracks, selects from the available formats.
 * @param liveEdgeLatencyMs For live streams, the number of milliseconds that the playback should
 *     lag behind the "live edge" (i.e. the end of the most recently defined media in the
 *     manifest). Choosing a small value will minimize latency introduced by the player, however
 *     note that the value sets an upper bound on the length of media that the player can buffer.
 *     Hence a small value may increase the probability of rebuffering and playback failures.
 * @param elapsedRealtimeOffsetMs If known, an estimate of the instantaneous difference between
 *     server-side unix time and {@link SystemClock#elapsedRealtime()} in milliseconds, specified
 *     as the server's unix time minus the local elapsed time. It unknown, set to 0.
 * @param eventHandler A handler to use when delivering events to {@code EventListener}. May be
 *     null if delivery of events is not required.
 * @param eventListener A listener of events. May be null if delivery of events is not required.
 * @param eventSourceId An identifier that gets passed to {@code eventListener} methods.
 */
public DashChunkSource(ManifestFetcher<MediaPresentationDescription> manifestFetcher,
    DashTrackSelector trackSelector, DataSource dataSource,
    FormatEvaluator adaptiveFormatEvaluator, long liveEdgeLatencyMs, long elapsedRealtimeOffsetMs,
    Handler eventHandler, EventListener eventListener, int eventSourceId) {
  this(manifestFetcher, manifestFetcher.getManifest(), trackSelector,
      dataSource, adaptiveFormatEvaluator, new SystemClock(), liveEdgeLatencyMs * 1000,
      elapsedRealtimeOffsetMs * 1000, true, eventHandler, eventListener, eventSourceId);
}