Decode Audio using MediaStreamSource

Question

I have a UWP project and I want to use the Windows.Media.Audio API to play a file. Instead of using the FileInputNode, I want to stream my file so I can precisely determine various timing properties.

I found the MediaStreamSource API and made the following code in an attempt to decode a 16 bit PCM 2 channel .wav File

 public async Task<Windows.Storage.Streams.Buffer> GetBuffer()
    {
        // check if the sample requested byte offset is within the file size 

        if (byteOffset + BufferSize <= mssStream.Size)
        {
            inputStream = mssStream.GetInputStreamAt(byteOffset);

            // create the MediaStreamSample and assign to the request object.  
            // You could also create the MediaStreamSample using createFromBuffer(...) 

            MediaStreamSample sample = await MediaStreamSample.CreateFromStreamAsync(inputStream, BufferSize, timeOffset);
            sample.Duration = sampleDuration;
            sample.KeyFrame = true;
            // increment the time and byte offset 

            byteOffset += BufferSize;
            timeOffset = timeOffset.Add(sampleDuration);


            return sample.Buffer;
        }
        else
        {

            return null;
        }
    }

Instead of using the Event system, I made a method that is fired whenever my AudioFrameInputNode needs a new AudioFrame.

Now it seems that the resulting byte array in the MediaStreamSample is exactly the same as when I simply read out my StorageFile using a DataReader.

Does MediaStreamSample.CreateFromStreamAsync actually decode the audiofile into a float byte array? Or is this done in the MediaElement when it plays back the sample?

And if so, how can I decode an audiofile so I can supply the resulting AudioBuffer back in to my FrameInputNode?

score 1 · Answer 1 · answered Mar 27 '16 at 18:15

When MediaStreamSample.CreateFromStreamAsync completes, it returns the new file as a MediaStreamSample.

If I understood what you want here is and example of what you can do to accomplish it.

function sampleRequestedHandler(e) {
    var request = e.request;
    if (!MyCustomFormatParser.IsAtEndOfStream(randomAccessStream)) { 
        var deferral = request.getDeferral();
        var inputStream = MyCustomFormatParser.getInputStream(randomAccessStream); 
        MediaStreamSample.createFromStreamAsync(inputStream, sampleSize, timeOffset).
            then(function(sample) {
                sample.duration = sampleDuration;  
                sample.keyFrame = true;  
                request.sample = sample;           
                deferral.complete();  
            });
        }
}

When sample is requested, your custom parser extracts audio data from RandomAccessStream and returns an InputStream of only audio samples

Decode Audio using MediaStreamSource

1 Answers1