media3/libraries/decoder_vp9/README.md

# VP9 decoder module

The VP9 module provides `LibvpxVideoRenderer`, which uses libvpx (the VPx
decoding library) to decode VP9 video.

## License note

Please note that whilst the code in this repository is licensed under
[Apache 2.0][], using this module also requires building and including one or
more external libraries as described below. These are licensed separately.

[Apache 2.0]: ../../LICENSE

## Build instructions (Linux, macOS)

To use the module you need to clone this GitHub project and depend on its
modules locally. Instructions for doing this can be found in the
[top level README][].

In addition, it's necessary to build the module's native components as follows:

* Set the following environment variables:

```
cd "<path to project checkout>"
VP9_MODULE_PATH="$(pwd)/libraries/decoder_vp9/src/main"
```

* Download the [Android NDK][] and set its location in an environment variable.
  This build configuration has been tested on NDK r21.

```
NDK_PATH="<path to Android NDK>"
```

* Fetch an appropriate branch of libvpx. We cannot guarantee compatibility
  with all versions of libvpx. We currently recommend version 1.8.0:

```
cd "<preferred location for libvpx>" && \
git clone https://chromium.googlesource.com/webm/libvpx && \
cd libvpx && \
git checkout tags/v1.8.0 -b v1.8.0 && \
LIBVPX_PATH="$(pwd)"
```

*   Add a link to the libvpx source code in the vp9 module `jni` directory and
    run a script that generates necessary configuration files for libvpx:

```
cd ${VP9_MODULE_PATH}/jni && \
ln -s "$LIBVPX_PATH" libvpx && \
./generate_libvpx_android_configs.sh
```

* Build the JNI native libraries from the command line:

```
cd "${VP9_MODULE_PATH}"/jni && \
${NDK_PATH}/ndk-build APP_ABI=all -j4
```

[top level README]: ../../README.md
[Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html

## Build instructions (Windows)

We do not provide support for building this module on Windows, however it should
be possible to follow the Linux instructions in [Windows PowerShell][].

[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell

## Notes

* Every time there is a change to the libvpx checkout:
  * Android config scripts should be re-generated by running
    `generate_libvpx_android_configs.sh`
  * Clean and re-build the project.
* If you want to use your own version of libvpx, point to it with the
  `${VP9_MODULE_PATH}/jni/libvpx` symlink. Please note that
  `generate_libvpx_android_configs.sh` and the makefiles may need to be modified
  to work with arbitrary versions of libvpx.

## Using the module with ExoPlayer

Once you've followed the instructions above to check out, build and depend on
the module, 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 `ExoPlayer.Builder`, you
    can enable using the module 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 `ExoPlayer.Builder`, 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.

## Rendering options

There are two possibilities for rendering the output `LibvpxVideoRenderer`
gets from the libvpx decoder:

*   GL rendering using GL shader for color space conversion

    *   If you are using `ExoPlayer` with `PlayerView`, enable this option by
        setting the `surface_type` of the view to be
        `video_decoder_gl_surface_view`.
    *   Otherwise, enable this option by sending `LibvpxVideoRenderer` a message
        of type `Renderer.MSG_SET_VIDEO_OUTPUT` with an instance of
        `VideoDecoderOutputBufferRenderer` as its object.
        `VideoDecoderGLSurfaceView` is the concrete
        `VideoDecoderOutputBufferRenderer` implementation used by `PlayerView`.

*   Native rendering using `ANativeWindow`

    *   If you are using `ExoPlayer` with `PlayerView`, this option is enabled
        by default.
    *   Otherwise, enable this option by sending `LibvpxVideoRenderer` a message
        of type `Renderer.MSG_SET_VIDEO_OUTPUT` with an instance of
        `SurfaceView` as its object.

Note: Although the default option uses `ANativeWindow`, based on our testing the
GL rendering mode has better performance, so should be preferred.

## Links

*   [Troubleshooting using decoding extensions][]

[Troubleshooting using decoding extensions]: https://developer.android.com/guide/topics/media/exoplayer/troubleshooting#how-can-i-get-a-decoding-library-to-load-and-be-used-for-playback