Using Windows.Media.Transcoding to create m4a from wav

Question

I'm trying to convert a wav file to an m4a file using the Transcoding classes. But every time I'm trying to get the PrepareTranscodeResult from my transcoder, I get an "Object reference not set to an instance of an object" exception.

I have looked at the Media Transcoding Sample from Microsoft, but that falls over in exactly the same fashion if I try to modify it for audio.

Any ideas where I'm going wrong?

        StorageFolder storageFolder = ApplicationData.Current.LocalFolder;
        file1 = await storageFolder.GetFileAsync("Foo.wav");
        file2 = await storageFolder.CreateFileAsync("Bar.m4a", CreationCollisionOption.ReplaceExisting);
        MediaTranscoder transcoder = new MediaTranscoder();
        var p = MediaEncodingProfile.CreateM4a(AudioEncodingQuality.Auto);

        try
        {
            var preparedTranscodeResult = await transcoder.PrepareFileTranscodeAsync(file1, file2, p);
            var progress = new Progress<double>(TranscodeProgress);
            await preparedTranscodeResult.TranscodeAsync().AsTask(progress);
        }
        catch (Exception exc)
        {
        }

Answer 1

You cannot use AudioEncodingQuality.Auto property without a video source.
In this case, you just have to use concrete property like this.

var p = MediaEncodingProfile.CreateM4a(AudioEncodingQuality.High);