Mark initial progressive source Timeline as placeholder

This is more accurate since it's just a placeholder and none of the
values is provided by the media.

It also allows to fix a problem in ClippingMediaSource where we
couldn't detect a clipping error because we didn't know if the
timeline is a placeholder or not.

Issue:#5924
PiperOrigin-RevId: 297813606

library/core/src/main/java/com/google/android/exoplayer2/source/ClippingMediaSource.java

@@ -319,14 +319,14 @@ public final class ClippingMediaSource extends CompositeMediaSource<Void> {
       }
       Window window = timeline.getWindow(0, new Window());
       startUs = Math.max(0, startUs);
+      if (!window.isPlaceholder && startUs != 0 && !window.isSeekable) {
+        throw new IllegalClippingException(IllegalClippingException.REASON_NOT_SEEKABLE_TO_START);
+      }
       long resolvedEndUs = endUs == C.TIME_END_OF_SOURCE ? window.durationUs : Math.max(0, endUs);
       if (window.durationUs != C.TIME_UNSET) {
         if (resolvedEndUs > window.durationUs) {
           resolvedEndUs = window.durationUs;
         }
-        if (startUs != 0 && !window.isSeekable) {
-          throw new IllegalClippingException(IllegalClippingException.REASON_NOT_SEEKABLE_TO_START);
-        }
         if (startUs > resolvedEndUs) {
           throw new IllegalClippingException(IllegalClippingException.REASON_START_EXCEEDS_END);
         }

library/core/src/main/java/com/google/android/exoplayer2/source/ProgressiveMediaSource.java

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.source;
 import android.net.Uri;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.drm.DrmSession;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.extractor.DefaultExtractorsFactory;
@@ -204,6 +205,7 @@ public final class ProgressiveMediaSource extends BaseMediaSource
   private final int continueLoadingCheckIntervalBytes;
   @Nullable private final Object tag;
 
+  private boolean timelineIsPlaceholder;
   private long timelineDurationUs;
   private boolean timelineIsSeekable;
   private boolean timelineIsLive;
@@ -226,6 +228,7 @@ public final class ProgressiveMediaSource extends BaseMediaSource
     this.loadableLoadErrorHandlingPolicy = loadableLoadErrorHandlingPolicy;
     this.customCacheKey = customCacheKey;
     this.continueLoadingCheckIntervalBytes = continueLoadingCheckIntervalBytes;
+    this.timelineIsPlaceholder = true;
     this.timelineDurationUs = C.TIME_UNSET;
     this.tag = tag;
   }
@@ -240,7 +243,7 @@ public final class ProgressiveMediaSource extends BaseMediaSource
   protected void prepareSourceInternal(@Nullable TransferListener mediaTransferListener) {
     transferListener = mediaTransferListener;
     drmSessionManager.prepare();
-    notifySourceInfoRefreshed(timelineDurationUs, timelineIsSeekable, timelineIsLive);
+    notifySourceInfoRefreshed();
   }
 
   @Override
@@ -283,30 +286,47 @@ public final class ProgressiveMediaSource extends BaseMediaSource
   public void onSourceInfoRefreshed(long durationUs, boolean isSeekable, boolean isLive) {
     // If we already have the duration from a previous source info refresh, use it.
     durationUs = durationUs == C.TIME_UNSET ? timelineDurationUs : durationUs;
-    if (timelineDurationUs == durationUs
+    if (!timelineIsPlaceholder
+        && timelineDurationUs == durationUs
         && timelineIsSeekable == isSeekable
         && timelineIsLive == isLive) {
       // Suppress no-op source info changes.
       return;
     }
-    notifySourceInfoRefreshed(durationUs, isSeekable, isLive);
+    timelineDurationUs = durationUs;
+    timelineIsSeekable = isSeekable;
+    timelineIsLive = isLive;
+    timelineIsPlaceholder = false;
+    notifySourceInfoRefreshed();
   }
 
   // Internal methods.
 
-  private void notifySourceInfoRefreshed(long durationUs, boolean isSeekable, boolean isLive) {
+  private void notifySourceInfoRefreshed() {
-    timelineDurationUs = durationUs;
-    timelineIsSeekable = isSeekable;
-    timelineIsLive = isLive;
     // TODO: Split up isDynamic into multiple fields to indicate which values may change. Then
     // indicate that the duration may change until it's known. See [internal: b/69703223].
-    refreshSourceInfo(
+    Timeline timeline =
         new SinglePeriodTimeline(
             timelineDurationUs,
             timelineIsSeekable,
             /* isDynamic= */ false,
             /* isLive= */ timelineIsLive,
             /* manifest= */ null,
-            tag));
+            tag);
+    if (timelineIsPlaceholder) {
+      // TODO: Actually prepare the extractors during prepatation so that we don't need a
+      // placeholder. See https://github.com/google/ExoPlayer/issues/4727.
+      timeline =
+          new ForwardingTimeline(timeline) {
+            @Override
+            public Window getWindow(
+                int windowIndex, Window window, long defaultPositionProjectionUs) {
+              super.getWindow(windowIndex, window, defaultPositionProjectionUs);
+              window.isPlaceholder = true;
+              return window;
+            }
+          };
+    }
+    refreshSourceInfo(timeline);
   }
 }

library/core/src/test/java/com/google/android/exoplayer2/source/ClippingMediaSourceTest.java

@@ -26,6 +26,7 @@ import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.Timeline.Period;
 import com.google.android.exoplayer2.Timeline.Window;
 import com.google.android.exoplayer2.source.ClippingMediaSource.IllegalClippingException;
+import com.google.android.exoplayer2.source.MaskingMediaSource.DummyTimeline;
 import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
 import com.google.android.exoplayer2.source.MediaSourceEventListener.EventDispatcher;
 import com.google.android.exoplayer2.testutil.FakeMediaPeriod;
@@ -100,6 +101,26 @@ public final class ClippingMediaSourceTest {
     }
   }
 
+  @Test
+  public void clippingUnseekableWindowWithUnknownDurationThrows() throws IOException {
+    Timeline timeline =
+        new SinglePeriodTimeline(
+            /* durationUs= */ C.TIME_UNSET,
+            /* isSeekable= */ false,
+            /* isDynamic= */ false,
+            /* isLive= */ false);
+
+    // If the unseekable window isn't clipped, clipping succeeds.
+    getClippedTimeline(timeline, /* startUs= */ 0, TEST_PERIOD_DURATION_US);
+    try {
+      // If the unseekable window is clipped, clipping fails.
+      getClippedTimeline(timeline, /* startUs= */ 1, TEST_PERIOD_DURATION_US);
+      fail("Expected clipping to fail.");
+    } catch (IllegalClippingException e) {
+      assertThat(e.reason).isEqualTo(IllegalClippingException.REASON_NOT_SEEKABLE_TO_START);
+    }
+  }
+
   @Test
   public void clippingStart() throws IOException {
     Timeline timeline =
@@ -139,9 +160,7 @@ public final class ClippingMediaSourceTest {
     // Timeline that's dynamic and not seekable. A child source might report such a timeline prior
     // to it having loaded sufficient data to establish its duration and seekability. Such timelines
     // should not result in clipping failure.
-    Timeline timeline =
+    Timeline timeline = new DummyTimeline(/* tag= */ null);
-        new SinglePeriodTimeline(
-            C.TIME_UNSET, /* isSeekable= */ false, /* isDynamic= */ true, /* isLive= */ true);
 
     Timeline clippedTimeline =
         getClippedTimeline(