FLAC for Windows Runtime

flac-winrt is a simple Windows Runtime component for decoding (so far) Free Lossless Audio Codec (FLAC) files. It is written completely in C++/CX, and is based on an original C libFLAC library and libFLAC++ version 1.3.0 source code. It is available for C# and C++/CX developers writing Windows Store apps for Windows (Phone) 8.1 and higher.

Currently, FLAC for Windows Runtime exposes only a decoder as this is what most developers would need in a Windows Store app. But as far as Windows Runtime matures and becomes a technology that is used in desktop development as well, FLAC for Windows Runtime will also update and add necessary functionality.

How to get

The recommended way to get FLAC for Windows Runtime package is to use NuGet: FLAC.WindowsRuntime

You can also download the latest release from this GitHub project.

Sample usage

To decode a FLAC file stream, use FLAC.WindowsRuntime.Decoder.StreamDecoder class. Instantiate the class and then call StreamDecoder.Init to initialize the decoder. Use Init() overload to provide your own FLAC decoder callbacks implementation, or use Init(IRandomAccessStream) overload to rely on internal FLAC for Windows Runtime implementation.

FLAC decoder callbacks are implemented as StreamDecoder class events. To get samples that the decoder returns, you will need to subscribe to StreamDecoder.WriteCallback event. The write callback contains an object of type FLAC.WindowsRuntime.Decoder.Callbacks.StreamDecoderWriteBuffer. This class wraps the multidimensional array of 32-bit integers provided by the stream decoder, and since Windows Runtime doesn't support exposing of multidimensional arrays you can get access to contents of the array using StreamDecoderWriteBuffer.GetData method that accepts first dimension index as a parameter. For convenience, StreamDecoderWriteBuffer.GetBuffer method is provided that packs the array to a Windows.Storage.Streams.IBuffer. This IBuffer is accepted by many Windows Runtime APIs. The StreamDecoder.WriteCallback event handler must return one of the FLAC.WindowsRuntime.Decoder.Callbacks.StreamDecoderWriteStatus enum values.

Coming soon: Example solution containing sample Windows Phone 8.1 background audio project that uses FLAC for Windows Runtime.

Here's an example of how FLAC.WindowsRuntime.Decoder.StreamDecoder should be used:

class FlacDecoder
{
    private readonly FLAC.WindowsRuntime.Decoder.StreamDecoder _streamDecoder;
    private Windows.Storage.Streams.IBuffer _currentSample;

    public FlacDecoder()
    {
        _streamDecoder = new FLAC.WindowsRuntime.Decoder.StreamDecoder();
        _streamDecoder.WriteCallback += WriteCallback;
    }
    
    public void Initialize(Windows.Storage.Streams.IRandomAccessStream fileStream)
    {
        if (!_streamDecoder.IsValid)
            throw new InvalidOperationException("Decoder is not valid.");
        
        FLAC.WindowsRuntime.Decoder.StreamDecoderInitStatus decoderInitStatus = _streamDecoder.Init(fileStream);
        if (decoderInitStatus != StreamDecoderInitStatus.OK)
        {
            Finish();
            throw new InvalidOperationException("Failed to initialize decoder.");
        }
    }
    
    public IBuffer GetSample()
    {
        // Note: FLAC API is synchronous
        return _streamDecoder.ProcessSingle() ? _currentSample : (_currentSample = null);
    }
    
    private FLAC.WindowsRuntime.Decoder.Callbacks.StreamDecoderWriteStatus WriteCallback(
        FLAC.WindowsRuntime.Format.Frame frame, FLAC.WindowsRuntime.Decoder.Callbacks.StreamDecoderWriteBuffer buffer)
    {
        _currentSample = buffer.GetBuffer();
        return StreamDecoderWriteStatus.Continue;
    }
    
    public void Finish()
    {
        _streamDecoder.Finish();
        _streamDecoder.WriteCallback -= WriteCallback;
        _streamDecoder.Dispose();
    }
}

How to build

flac-winrt includes all the necessary source code to build the libraries. FLAC for Windows Runtime solution includes original libFLAC and its dependencies, including libogg, and contains libFLAC_winrt project that is the main output of the solution.

You will need Visual Studio 2013 or higher to build the library for Windows (Phone) 8.1 or higher. All the projects currently are set up to build for Windows Phone 8.1, but it's easy to retarget them for Windows 8.1 or higher.

How to contribute

Please refer to Contribution guidelines. Thank you :)