README updates for misc modules

PiperOrigin-RevId: 402292139

demos/cast/README.md

-# Cast demo application
+# Cast demo
 
 
-This folder contains a demo application that showcases ExoPlayer integration
-with Google Cast.
+This app demonstrates integration with Google Cast, as well as switching between
+Google Cast and local playback using ExoPlayer.
 
 
-Please see the [demos README](../README.md) for instructions on how to build and
-run this demo.
+See the [demos README](../README.md) for instructions on how to build and run
+this demo.

demos/main/README.md

 # ExoPlayer main demo
 # ExoPlayer main demo
 
 
-This is the main ExoPlayer demo application. It uses ExoPlayer to play a number
-of test streams. It can be used as a starting point or reference project when
-developing other applications that make use of the ExoPlayer library.
+This is the main ExoPlayer demo app. It uses ExoPlayer to play a number of test
+streams. It can be used as a starting point or reference project when developing
+other applications that make use of the ExoPlayer library.
 
 
-Please see the [demos README](../README.md) for instructions on how to build and
-run this demo.
+See the [demos README](../README.md) for instructions on how to build and run
+this demo.

demos/surface/README.md

@@ -18,7 +18,7 @@ called, and because you can move output off-screen easily (`setOutputSurface`
 can't take a `null` surface, so the player has to use a `DummySurface`, which
 can't take a `null` surface, so the player has to use a `DummySurface`, which
 doesn't handle protected output on all devices).
 doesn't handle protected output on all devices).
 
 
-Please see the [demos README](../README.md) for instructions on how to build and
-run this demo.
+See the [demos README](../README.md) for instructions on how to build and run
+this demo.
 
 
 [SurfaceControl]: https://developer.android.com/reference/android/view/SurfaceControl
 [SurfaceControl]: https://developer.android.com/reference/android/view/SurfaceControl

library/common/README.md

-# ExoPlayer common library module
+# Common module
 
 
-Common code used by other ExoPlayer modules.
+Provides common code and utilities used by other media modules. Application code
+will not normally need to depend on this module directly.
 
 
 ## Links
 ## Links
 
 
 *   [Javadoc][]: Note that this Javadoc is combined with that of other modules.
 *   [Javadoc][]: Note that this Javadoc is combined with that of other modules.
 
 
 [Javadoc]: https://exoplayer.dev/doc/reference/index.html
 [Javadoc]: https://exoplayer.dev/doc/reference/index.html
-

library/extractor/README.md

-# ExoPlayer extractor library module
+# Extractor module
 
 
-Provides media container extractors.
+Provides media container extractors and related utilities. Application code will
+not normally need to depend on this module directly.
 
 
 ## Links
 ## Links
 
 

library/transformer/README.md

-# ExoPlayer transformer library module
+# Transformer module
 
 
-Provides support for transforming media files.
+Provides functionality for transforming media files.
+
+## Getting the module
+
+The easiest way to get the module is to add it as a gradle dependency:
+
+```gradle
+implementation 'com.google.android.exoplayer:exoplayer-transformer:2.X.X'
+```
+
+where `2.X.X` is the version, which must match the version of the other media
+modules being used.
+
+Alternatively, you can clone this GitHub project and depend on the module
+locally. Instructions for doing this can be found in the [top level README][].
+
+[top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
+
+## Using the module
+
+Use of the Transformer module is documented in the
+[developer guide](https://exoplayer.dev/transforming-media.html).
 
 
 ## Links
 ## Links
 
 
-* [Javadoc][]: Classes matching `com.google.android.exoplayer2.transformer.*`
-  belong to this module.
+*   [Javadoc][]: Classes matching `com.google.android.exoplayer2.transformer.*` belong to this
+    module.
 
 
 [Javadoc]: https://exoplayer.dev/doc/reference/index.html
 [Javadoc]: https://exoplayer.dev/doc/reference/index.html