Update documentation with new demo app location

Plus a few misc doc fixes / adjustments

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=166323135

README.md

@@ -71,12 +71,12 @@ individually.
 In addition to library modules, ExoPlayer has multiple extension modules that
 depend on external libraries to provide additional functionality. Some
 extensions are available from JCenter, whereas others must be built manaully.
-Browse the [extensions directory] and their individual READMEs for details.
+Browse the [extensions directory][] and their individual READMEs for details.
 
 More information on the library and extension modules that are available from
 JCenter can be found on [Bintray][].
 
-[extensions directory][]: https://github.com/google/ExoPlayer/tree/release-v2/extensions/
+[extensions directory]: https://github.com/google/ExoPlayer/tree/release-v2/extensions/
 [Bintray]: https://bintray.com/google/exoplayer
 
 ### Locally ###

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java

@@ -211,12 +211,18 @@ public interface ExoPlayer extends Player {
   /**
    * Prepares the player to play the provided {@link MediaSource}. Equivalent to
    * {@code prepare(mediaSource, true, true)}.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to prepare a
+   * player more than once with the same piece of media, use a new instance each time.
    */
   void prepare(MediaSource mediaSource);
 
   /**
    * Prepares the player to play the provided {@link MediaSource}, optionally resetting the playback
    * position the default position in the first {@link Timeline.Window}.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to prepare a
+   * player more than once with the same piece of media, use a new instance each time.
    *
    * @param mediaSource The {@link MediaSource} to play.
    * @param resetPosition Whether the playback position should be reset to the default position in

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

@@ -87,6 +87,9 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
   /**
    * Appends a {@link MediaSource} to the playlist.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to add the same
+   * piece of media multiple times, use a new instance each time.
    *
    * @param mediaSource The {@link MediaSource} to be added to the list.
    */
@@ -96,6 +99,9 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
   /**
    * Adds a {@link MediaSource} to the playlist.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to add the same
+   * piece of media multiple times, use a new instance each time.
    *
    * @param index The index at which the new {@link MediaSource} will be inserted. This index must
    *     be in the range of 0 &lt;= index &lt;= {@link #getSize()}.
@@ -112,6 +118,9 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
   /**
    * Appends multiple {@link MediaSource}s to the playlist.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to add the same
+   * piece of media multiple times, use a new instance each time.
    *
    * @param mediaSources A collection of {@link MediaSource}s to be added to the list. The media
    *     sources are added in the order in which they appear in this collection.
@@ -122,6 +131,9 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
   /**
    * Adds multiple {@link MediaSource}s to the playlist.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used. If you want to add the same
+   * piece of media multiple times, use a new instance each time.
    *
    * @param index The index at which the new {@link MediaSource}s will be inserted. This index must
    *     be in the range of 0 &lt;= index &lt;= {@link #getSize()}.
@@ -142,6 +154,10 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
   /**
    * Removes a {@link MediaSource} from the playlist.
+   * <p>
+   * Note: {@link MediaSource} instances are not designed to be re-used, and so the instance being
+   * removed should not be re-added. If you want to move the instance use
+   * {@link #moveMediaSource(int, int)} instead.
    *
    * @param index The index at which the media source will be removed. This index must be in the
    *     range of 0 &lt;= index &lt; {@link #getSize()}.