Update extension README with usage instructions

Issue: #3162

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=165572088

extensions/ffmpeg/README.md

@@ -2,17 +2,18 @@
 
 ## Description ##
 
-The FFmpeg extension is a [Renderer][] implementation that uses FFmpeg to decode
-audio.
-
-[Renderer]: https://google.github.io/ExoPlayer/doc/reference/com/google/android/exoplayer2/Renderer.html
+The FFmpeg extension provides `FfmpegAudioRenderer`, which uses FFmpeg for
+decoding and can render audio encoded in a variety of formats.
 
 ## Build instructions ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
-[top level README][]. In addition, it's necessary to build the extension's
-native components as follows:
+[top level README][]. The extension is not provided via JCenter (see [#2781][]
+for more information).
+
+In addition, it's necessary to build the extension's native components as
+follows:
 
 * Set the following environment variables:
 
@@ -34,7 +35,11 @@ NDK_PATH="<path to Android NDK>"
 HOST_PLATFORM="linux-x86_64"
 ```
 
-* Fetch and build FFmpeg. For example, to fetch and build for armeabi-v7a,
+* Fetch and build FFmpeg. The configuration flags determine which formats will
+  be supported. See the [Supported formats][] page for more details of the
+  available flags.
+
+For example, to fetch and build for armeabi-v7a,
   arm64-v8a and x86 on Linux x86_64:
 
 ```
@@ -103,5 +108,35 @@ cd "${FFMPEG_EXT_PATH}"/jni && \
 ${NDK_PATH}/ndk-build APP_ABI="armeabi-v7a arm64-v8a x86" -j4
 ```
 
+## Using the extension ##
+
+Once you've followed the instructions above to check out, build and depend on
+the extension, the next step is to tell ExoPlayer to use `FfmpegAudioRenderer`.
+How you do this depends on which player API you're using:
+
+* If you're passing a `DefaultRenderersFactory` to
+  `ExoPlayerFactory.newSimpleInstance`, you can enable using the extension by
+  setting the `extensionRendererMode` parameter of the `DefaultRenderersFactory`
+  constructor to `EXTENSION_RENDERER_MODE_ON`. This will use
+  `FfmpegAudioRenderer` for playback if `MediaCodecAudioRenderer` doesn't
+  support the input format. Pass `EXTENSION_RENDERER_MODE_PREFER` to give
+  `FfmpegAudioRenderer` priority over `MediaCodecAudioRenderer`.
+* If you've subclassed `DefaultRenderersFactory`, add an `FfmpegAudioRenderer`
+  to the output list in `buildAudioRenderers`. ExoPlayer will use the first
+  `Renderer` in the list that supports the input media format.
+* If you've implemented your own `RenderersFactory`, return an
+  `FfmpegAudioRenderer` instance from `createRenderers`. ExoPlayer will use the
+  first `Renderer` in the returned array that supports the input media format.
+* If you're using `ExoPlayerFactory.newInstance`, pass an `FfmpegAudioRenderer`
+  in the array of `Renderer`s. ExoPlayer will use the first `Renderer` in the
+  list that supports the input media format.
+
+Note: These instructions assume you're using `DefaultTrackSelector`. If you have
+a custom track selector the choice of `Renderer` is up to your implementation,
+so you need to make sure you are passing an `FfmpegAudioRenderer` to the player,
+then implement your own logic to use the renderer for a given track.
+
 [top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
 [Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
+[#2781]: https://github.com/google/ExoPlayer/issues/2781
+[Supported formats]: https://google.github.io/ExoPlayer/supported-formats.html#ffmpeg-extension

extensions/flac/README.md

@@ -2,18 +2,17 @@
 
 ## Description ##
 
-The Flac extension is a [Renderer][] implementation that helps you bundle
-libFLAC (the Flac decoding library) into your app and use it along with
-ExoPlayer to play Flac audio on Android devices.
-
-[Renderer]: https://google.github.io/ExoPlayer/doc/reference/com/google/android/exoplayer2/Renderer.html
+The Flac extension provides `FlacExtractor` and `LibflacAudioRenderer`, which
+use libFLAC (the Flac decoding library) to extract and decode FLAC audio.
 
 ## Build instructions ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
-[top level README][]. In addition, it's necessary to build the extension's
-native components as follows:
+[top level README][].
+
+In addition, it's necessary to build the extension's native components as
+follows:
 
 * Set the following environment variables:
 
@@ -46,3 +45,40 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
 
 [top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
 [Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
+
+## Using the extension ##
+
+Once you've followed the instructions above to check out, build and depend on
+the extension, the next step is to tell ExoPlayer to use the extractor and/or
+renderer.
+
+### Using `FlacExtractor` ###
+
+`FlacExtractor` is used via `ExtractorMediaSource`. If you're using
+`DefaultExtractorsFactory`, `FlacExtractor` will automatically be used to read
+`.flac` files. If you're not using `DefaultExtractorsFactory`, return a
+`FlacExtractor` from your `ExtractorsFactory.createExtractors` implementation.
+
+### Using `LibflacAudioRenderer` ###
+
+* If you're passing a `DefaultRenderersFactory` to
+  `ExoPlayerFactory.newSimpleInstance`, you can enable using the extension by
+  setting the `extensionRendererMode` parameter of the `DefaultRenderersFactory`
+  constructor to `EXTENSION_RENDERER_MODE_ON`. This will use
+  `LibflacAudioRenderer` for playback if `MediaCodecAudioRenderer` doesn't
+  support the input format. Pass `EXTENSION_RENDERER_MODE_PREFER` to give
+  `LibflacAudioRenderer` priority over `MediaCodecAudioRenderer`.
+* If you've subclassed `DefaultRenderersFactory`, add a `LibflacAudioRenderer`
+  to the output list in `buildAudioRenderers`. ExoPlayer will use the first
+  `Renderer` in the list that supports the input media format.
+* If you've implemented your own `RenderersFactory`, return a
+  `LibflacAudioRenderer` instance from `createRenderers`. ExoPlayer will use the
+  first `Renderer` in the returned array that supports the input media format.
+* If you're using `ExoPlayerFactory.newInstance`, pass a `LibflacAudioRenderer`
+  in the array of `Renderer`s. ExoPlayer will use the first `Renderer` in the
+  list that supports the input media format.
+
+Note: These instructions assume you're using `DefaultTrackSelector`. If you have
+a custom track selector the choice of `Renderer` is up to your implementation,
+so you need to make sure you are passing an `LibflacAudioRenderer` to the
+player, then implement your own logic to use the renderer for a given track.

extensions/opus/README.md

@@ -2,18 +2,17 @@
 
 ## Description ##
 
-The Opus extension is a [Renderer][] implementation that helps you bundle
-libopus (the Opus decoding library) into your app and use it along with
-ExoPlayer to play Opus audio on Android devices.
-
-[Renderer]: https://google.github.io/ExoPlayer/doc/reference/com/google/android/exoplayer2/Renderer.html
+The Opus extension provides `LibopusAudioRenderer`, which uses
+libopus (the Opus decoding library) to decode Opus audio.
 
 ## Build instructions ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
-[top level README][]. In addition, it's necessary to build the extension's
-native components as follows:
+[top level README][].
+
+In addition, it's necessary to build the extension's native components as
+follows:
 
 * Set the following environment variables:
 
@@ -59,3 +58,31 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
   * Clean and re-build the project.
 * If you want to use your own version of libopus, place it in
   `${OPUS_EXT_PATH}/jni/libopus`.
+
+## Using the extension ##
+
+Once you've followed the instructions above to check out, build and depend on
+the extension, the next step is to tell ExoPlayer to use `LibopusAudioRenderer`.
+How you do this depends on which player API you're using:
+
+* If you're passing a `DefaultRenderersFactory` to
+  `ExoPlayerFactory.newSimpleInstance`, you can enable using the extension by
+  setting the `extensionRendererMode` parameter of the `DefaultRenderersFactory`
+  constructor to `EXTENSION_RENDERER_MODE_ON`. This will use
+  `LibopusAudioRenderer` for playback if `MediaCodecAudioRenderer` doesn't
+  support the input format. Pass `EXTENSION_RENDERER_MODE_PREFER` to give
+  `LibopusAudioRenderer` priority over `MediaCodecAudioRenderer`.
+* If you've subclassed `DefaultRenderersFactory`, add a `LibopusAudioRenderer`
+  to the output list in `buildAudioRenderers`. ExoPlayer will use the first
+  `Renderer` in the list that supports the input media format.
+* If you've implemented your own `RenderersFactory`, return a
+  `LibopusAudioRenderer` instance from `createRenderers`. ExoPlayer will use the
+  first `Renderer` in the returned array that supports the input media format.
+* If you're using `ExoPlayerFactory.newInstance`, pass a `LibopusAudioRenderer`
+  in the array of `Renderer`s. ExoPlayer will use the first `Renderer` in the
+  list that supports the input media format.
+
+Note: These instructions assume you're using `DefaultTrackSelector`. If you have
+a custom track selector the choice of `Renderer` is up to your implementation,
+so you need to make sure you are passing an `LibopusAudioRenderer` to the
+player, then implement your own logic to use the renderer for a given track.

extensions/vp9/README.md

@@ -2,18 +2,17 @@
 
 ## Description ##
 
-The VP9 extension is a [Renderer][] implementation that helps you bundle libvpx
-(the VP9 decoding library) into your app and use it along with ExoPlayer to play
-VP9 video on Android devices.
-
-[Renderer]: https://google.github.io/ExoPlayer/doc/reference/com/google/android/exoplayer2/Renderer.html
+The VP9 extension provides `LibvpxVideoRenderer`, which uses
+libvpx (the VPx decoding library) to decode VP9 video.
 
 ## Build instructions ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
-[top level README][]. In addition, it's necessary to build the extension's
-native components as follows:
+[top level README][].
+
+In addition, it's necessary to build the extension's native components as
+follows:
 
 * Set the following environment variables:
 
@@ -76,3 +75,38 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
   `${VP9_EXT_PATH}/jni/libvpx` or `${VP9_EXT_PATH}/jni/libyuv` respectively. But
   please note that `generate_libvpx_android_configs.sh` and the makefiles need
   to be modified to work with arbitrary versions of libvpx and libyuv.
+
+## Using the extension ##
+
+Once you've followed the instructions above to check out, build and depend on
+the extension, the next step is to tell ExoPlayer to use `LibvpxVideoRenderer`.
+How you do this depends on which player API you're using:
+
+* If you're passing a `DefaultRenderersFactory` to
+  `ExoPlayerFactory.newSimpleInstance`, you can enable using the extension by
+  setting the `extensionRendererMode` parameter of the `DefaultRenderersFactory`
+  constructor to `EXTENSION_RENDERER_MODE_ON`. This will use
+  `LibvpxVideoRenderer` for playback if `MediaCodecVideoRenderer` doesn't
+  support decoding the input VP9 stream. Pass `EXTENSION_RENDERER_MODE_PREFER`
+  to give `LibvpxVideoRenderer` priority over `MediaCodecVideoRenderer`.
+* If you've subclassed `DefaultRenderersFactory`, add a `LibvpxVideoRenderer`
+  to the output list in `buildVideoRenderers`. ExoPlayer will use the first
+  `Renderer` in the list that supports the input media format.
+* If you've implemented your own `RenderersFactory`, return a
+  `LibvpxVideoRenderer` instance from `createRenderers`. ExoPlayer will use the
+  first `Renderer` in the returned array that supports the input media format.
+* If you're using `ExoPlayerFactory.newInstance`, pass a `LibvpxVideoRenderer`
+  in the array of `Renderer`s. ExoPlayer will use the first `Renderer` in the
+  list that supports the input media format.
+
+Note: These instructions assume you're using `DefaultTrackSelector`. If you have
+a custom track selector the choice of `Renderer` is up to your implementation,
+so you need to make sure you are passing an `LibvpxVideoRenderer` to the
+player, then implement your own logic to use the renderer for a given track.
+
+`LibvpxVideoRenderer` can optionally output to a `VpxVideoSurfaceView` when not
+being used via `SimpleExoPlayer`, in which case color space conversion will be
+performed using a GL shader. To enable this mode, send the renderer a message of
+type `LibvpxVideoRenderer.MSG_SET_OUTPUT_BUFFER_RENDERER` with the
+`VpxVideoSurfaceView` as its object, instead of sending `MSG_SET_SURFACE` with a
+`Surface`.