Fail at preparation when trying to download live content.

PiperOrigin-RevId: 275293735

demos/main/src/main/java/com/google/android/exoplayer2/demo/DownloadTracker.java

@@ -216,7 +216,12 @@ public class DownloadTracker {
     @Override
     public void onPrepareError(DownloadHelper helper, IOException e) {
       Toast.makeText(context, R.string.download_start_error, Toast.LENGTH_LONG).show();
-      Log.e(TAG, "Failed to start download", e);
+      Log.e(
+          TAG,
+          e instanceof DownloadHelper.LiveContentUnsupportedException
+              ? "Downloading live content unsupported"
+              : "Failed to start download",
+          e);
     }
 
     // DialogInterface.OnClickListener implementation.

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java

@@ -137,6 +137,9 @@ public final class DownloadHelper {
     void onPrepareError(DownloadHelper helper, IOException e);
   }
 
+  /** Thrown at an attempt to download live content. */
+  public static class LiveContentUnsupportedException extends IOException {}
+
   @Nullable
   private static final Constructor<? extends MediaSourceFactory> DASH_FACTORY_CONSTRUCTOR =
       getConstructor("com.google.android.exoplayer2.source.dash.DashMediaSource$Factory");
@@ -999,6 +1002,14 @@ public final class DownloadHelper {
         // Ignore dynamic updates.
         return;
       }
+      if (timeline.getWindow(/* windowIndex= */ 0, new Timeline.Window()).isLive) {
+        downloadHelperHandler
+            .obtainMessage(
+                DOWNLOAD_HELPER_CALLBACK_MESSAGE_FAILED,
+                /* obj= */ new LiveContentUnsupportedException())
+            .sendToTarget();
+        return;
+      }
       this.timeline = timeline;
       mediaPeriods = new MediaPeriod[timeline.getPeriodCount()];
       for (int i = 0; i < mediaPeriods.length; i++) {