# Flac decoder module

The Flac module provides `FlacExtractor` and `LibflacAudioRenderer`, which use
libFLAC (the Flac decoding library) to extract and decode FLAC audio.

## 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 fetch libflac as follows:

* Set the following environment variables:

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

* Fetch libflac:

```
cd "${FLAC_MODULE_PATH}/jni" && \
git clone https://github.com/xiph/flac.git libflac
```

* [Install CMake][]

Having followed these steps, gradle will build the module automatically when run
on the command line or via Android Studio, using [CMake][] and [Ninja][] to
configure and build libflac and the module's [JNI wrapper library][].

[top level README]: ../../README.md
[Install CMake]: https://developer.android.com/studio/projects/install-ndk
[CMake]: https://cmake.org/
[Ninja]: https://ninja-build.org
[JNI wrapper library]: src/main/jni/flac_jni.cc

## 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

## Using the module

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 the extractor and/or
renderer.

### Using `FlacExtractor`

`FlacExtractor` is used via `ProgressiveMediaSource`. 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` with ExoPlayer

*   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 `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 `ExoPlayer.Builder`, 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.

## Links

*   [Troubleshooting using decoding extensions][]

[Troubleshooting using decoding extensions]: https://developer.android.com/media/media3/exoplayer/troubleshooting#how-can-i-get-a-decoding-library-to-load-and-be-used-for-playback