diff --git a/demo/src/main/java/com/google/android/exoplayer2/demo/EventLogger.java b/demo/src/main/java/com/google/android/exoplayer2/demo/EventLogger.java
index bb61776408..eac68b2f32 100644
--- a/demo/src/main/java/com/google/android/exoplayer2/demo/EventLogger.java
+++ b/demo/src/main/java/com/google/android/exoplayer2/demo/EventLogger.java
@@ -96,8 +96,7 @@ import java.util.Locale;
     int periodCount = timeline.getPeriodCount();
     int seekWindowCount = timeline.getSeekWindowCount();
     Log.d(TAG, "sourceInfo[isFinal=" + isFinal + ", startTime=" + timeline.getAbsoluteStartTime()
-        + ", periodCount=" + (periodCount == Timeline.UNKNOWN_PERIOD_COUNT ? "?" : periodCount)
-        + ", seekWindows: " + seekWindowCount);
+        + ", periodCount=" + periodCount + ", seekWindows: " + seekWindowCount);
     for (int seekWindowIndex = 0; seekWindowIndex < seekWindowCount; seekWindowIndex++) {
       Log.d(TAG, "  " + timeline.getSeekWindow(seekWindowIndex));
     }
diff --git a/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java b/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
index c8a8478304..f97b99b798 100644
--- a/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
+++ b/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
@@ -18,7 +18,6 @@ package com.google.android.exoplayer2.source;
 import com.google.android.exoplayer2.util.Util;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Arrays;
 
 /**
  * Concatenates multiple {@link MediaSource}s.
@@ -124,26 +123,18 @@ public final class ConcatenatingMediaSource implements MediaSource {
           SeekWindow sourceSeekWindow = timeline.getSeekWindow(j);
           concatenatedSeekWindows.add(sourceSeekWindow.copyOffsetByPeriodCount(sourceOffset));
         }
-        int periodCount = timeline.getPeriodCount();
-        if (periodCount == Timeline.UNKNOWN_PERIOD_COUNT) {
-          sourceOffsets = Arrays.copyOf(sourceOffsets, i);
-          isFinal = false;
-          break;
-        }
-        sourceOffset += periodCount;
+        sourceOffset += timeline.getPeriodCount();
         sourceOffsets[i] = sourceOffset;
       }
       this.timelines = timelines;
       this.isFinal = isFinal;
       this.sourceOffsets = sourceOffsets;
-      seekWindows =
-          concatenatedSeekWindows.toArray(new SeekWindow[concatenatedSeekWindows.size()]);
+      seekWindows = concatenatedSeekWindows.toArray(new SeekWindow[concatenatedSeekWindows.size()]);
     }
 
     @Override
     public int getPeriodCount() {
-      return sourceOffsets.length == timelines.length ? sourceOffsets[sourceOffsets.length - 1]
-          : UNKNOWN_PERIOD_COUNT;
+      return sourceOffsets[sourceOffsets.length - 1];
     }
 
     @Override
diff --git a/library/src/main/java/com/google/android/exoplayer2/source/SeekWindow.java b/library/src/main/java/com/google/android/exoplayer2/source/SeekWindow.java
index 61a5207498..87e0baec5d 100644
--- a/library/src/main/java/com/google/android/exoplayer2/source/SeekWindow.java
+++ b/library/src/main/java/com/google/android/exoplayer2/source/SeekWindow.java
@@ -39,7 +39,7 @@ public final class SeekWindow {
    * @param startTimeUs The start time of the window in microseconds, relative to the start of the
    *     specified start period.
    * @param endPeriodIndex The index of the period containing the end of the window.
-   * @param endTimeUs = The end time of the window in microseconds, relative to the start of the
+   * @param endTimeUs The end time of the window in microseconds, relative to the start of the
    *     specified end period.
    */
   public static SeekWindow createWindow(int startPeriodIndex, long startTimeUs,
diff --git a/library/src/main/java/com/google/android/exoplayer2/source/Timeline.java b/library/src/main/java/com/google/android/exoplayer2/source/Timeline.java
index 17d7113ebc..0b344d38d5 100644
--- a/library/src/main/java/com/google/android/exoplayer2/source/Timeline.java
+++ b/library/src/main/java/com/google/android/exoplayer2/source/Timeline.java
@@ -22,11 +22,6 @@ import com.google.android.exoplayer2.ExoPlayer;
  */
 public interface Timeline {
 
-  /**
-   * Returned by {@link #getPeriodCount()} when the number of periods is not known.
-   */
-  int UNKNOWN_PERIOD_COUNT = -1;
-
   /**
    * Returned by {@link #getIndexOfPeriod(Object)} if no period index corresponds to the specified
    * identifier.
@@ -34,8 +29,7 @@ public interface Timeline {
   int NO_PERIOD_INDEX = -1;
 
   /**
-   * Returns the number of periods in the timeline, or {@link #UNKNOWN_PERIOD_COUNT} if not known.
-   * If {@link #isFinal()} returns {@code true}, the number of periods must be known.
+   * Returns the number of periods in the timeline.
    */
   int getPeriodCount();
 
diff --git a/library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java b/library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java
index ee0f0b95bb..7ba1878600 100644
--- a/library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java
+++ b/library/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java
@@ -142,7 +142,7 @@ public final class DashMediaSource implements MediaSource {
   public int getNewPlayingPeriodIndex(int oldPlayingPeriodIndex, Timeline oldTimeline) {
     int periodIndex = oldPlayingPeriodIndex;
     int oldPeriodCount = oldTimeline.getPeriodCount();
-    while (oldPeriodCount == Timeline.UNKNOWN_PERIOD_COUNT || periodIndex < oldPeriodCount) {
+    while (periodIndex < oldPeriodCount) {
       Object id = oldTimeline.getPeriodId(periodIndex);
       if (id == null) {
         break;