CODEWITHSUNDEEP
c#audiowindows-phone-8.1windows-phoneoverlapping
user3546242
user3546242

Reputation:

WP8.1 - C# - Overlapping audio with MediaComposition class

I am developing a voice recorder app for Windows Phone 8.1 that stores the recordings on the local storage and a cloud storage service.

Everything's almost done except the fact that being able to pause an ongoing recording is a strong requirement for this app and I have to get it done. Now, since PauseRecordAsync() and ResumeRecordAsync() are not available for Windows Phone 8.1 in the MediaCapture class but they will be available in Windows 10, I had to make a workaround: Every time the pause button is pressed, an audio chunk is saved in the temp folder and that file is stored in an array. When the stop button is pressed, the last chunk is stored in the array and the following Concatenation function is called and a final audio temp file is created:

public async Task<IStorageFile> ConcatenateAudio([ReadOnlyArray]IStorageFile[] audioFiles, IStorageFolder outputFolder, string outputfileName)
    {
            IStorageFile _OutputFile = await outputFolder.CreateFileAsync(outputfileName, CreationCollisionOption.ReplaceExisting);
            MediaComposition _MediaComposition = new MediaComposition();
            MediaEncodingProfile _MediaEncodingProfile = MediaEncodingProfile.CreateM4a(AudioEncodingQuality.High);
            foreach (IStorageFile _AudioFile in audioFiles)
            {
                if(_AudioFile != null)
                {
                    BackgroundAudioTrack _BackgroundAudioTrack = await BackgroundAudioTrack.CreateFromFileAsync(_AudioFile);
                    MediaClip _MediaClip = MediaClip.CreateFromColor(Windows.UI.Colors.Black, _BackgroundAudioTrack.TrimmedDuration); // A dummy black video is created witn the size of the current audio chunk. 
                                                                                                                                      // Without this, the duration of the MediaComposition object is always 0. 
                                                                                                                                      // It's a messy workaround but it gets the job done. 
                                                                                                                                      // Windows 10 will dirrectly support PauseRecordAsync() and ResumeRecordAsync() for MediaCapture tho'. Yay! :D
                    _MediaClip.Volume = 0;
                    _BackgroundAudioTrack.Volume = 1;
                    _MediaComposition.Clips.Add(_MediaClip);
                    _MediaComposition.BackgroundAudioTracks.Add(_BackgroundAudioTrack);
                }
            }
            TranscodeFailureReason _TranscodeFailureReason = await _MediaComposition.RenderToFileAsync(_OutputFile, MediaTrimmingPreference.Fast, _MediaEncodingProfile);
            if (_TranscodeFailureReason != TranscodeFailureReason.None)
            {
                throw new Exception("Audio Concatenation Failed: " + _TranscodeFailureReason.ToString());
            }
            return _OutputFile;
    }

The problem is that when I play the file, all the audio chunks are played from the beginning of the final audio file at the same time instead of playing the second one right after the first one ended and so on. They are all playing one over the other. The length of the file on the other hand is correct and after all audio files finished playing, it's total silence.

Upvotes: 0

Views: 246

Answers (1)

user3546242
user3546242

Reputation:

I figured it out. I had to manually set the delay for BackgroundAudioTrack. Here is the working code:

public async Task<IStorageFile> ConcatenateAudio([ReadOnlyArray]IStorageFile[] audioFiles, IStorageFolder outputFolder, string outputfileName)
    {
        IStorageFile _OutputFile = await outputFolder.CreateFileAsync(outputfileName, CreationCollisionOption.ReplaceExisting);
        MediaComposition _MediaComposition = new MediaComposition();
        MediaEncodingProfile _MediaEncodingProfile = MediaEncodingProfile.CreateM4a(AudioEncodingQuality.High);
        TimeSpan totalDelay = TimeSpan.Zero;
        foreach (IStorageFile _AudioFile in audioFiles)
        {
            if (_AudioFile != null)
            {
                BackgroundAudioTrack _BackgroundAudioTrack = await BackgroundAudioTrack.CreateFromFileAsync(_AudioFile);

                MediaClip _MediaClip = MediaClip.CreateFromColor(Windows.UI.Colors.Black, _BackgroundAudioTrack.TrimmedDuration); // A dummy black video is created witn the size of the current audio chunk. 
                                                                                                                                  // Without this, the duration of the MediaComposition object is always 0. 
                                                                                                                                  // It's a messy workaround but it gets the job done. 
                                                                                                                                  // Windows 10 will dirrectly support PauseRecordAsync() and ResumeRecordAsync() for MediaCapture tho'. Yay! :D
                _MediaClip.Volume = 0;
                _BackgroundAudioTrack.Volume = 1;
                _MediaComposition.Clips.Add(_MediaClip);
                _MediaComposition.BackgroundAudioTracks.Add(_BackgroundAudioTrack);
                _BackgroundAudioTrack.Delay = totalDelay;
                totalDelay += _BackgroundAudioTrack.TrimmedDuration;
            }
        }
        TranscodeFailureReason _TranscodeFailureReason = await _MediaComposition.RenderToFileAsync(_OutputFile, MediaTrimmingPreference.Fast, _MediaEncodingProfile);
        if (_TranscodeFailureReason != TranscodeFailureReason.None)
        {
            throw new Exception("Audio Concatenation Failed: " + _TranscodeFailureReason.ToString());
        }
        return _OutputFile;
    }

Upvotes: 2

Related Questions