C#+VideoLan.LibVLC Sample Audio Stream and save it to disk

Question

I am using VideoLan.VLC to get 20 seconds of an audio stream every 30 seconds. I have a loop, something like

    private LibVLC libvlc = new LibVLC();
    private MediaPlayer mediaPlayer = null;
    private Media Media = null;

    private string AudioSampleFileName { get {
                return "audio_" + DateTime.Now.ToString("yyyyMMdd_HHmmss")+
                        ".ts";             
            } }

public void Start(){

     mediaPlayer = new MediaPlayer(libvlc);
     
     while(...){
             Get_20_seconds_audio_sample();
             Wait_30_Seconds();            
            }
          }



    public void Get_sample(Uri playPathUri, string FileName)
            {
                
                var currentDirectory = Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);
                var destination = Path.Combine(currentDirectory, FileName);
    
                var mediaOptions = new string[]
                {
                     ":sout=#file{dst=" + destination + ",channels=1,samplerate=16000}",
                     ":sout-keep"
                };
                
                if (Media == null)
                {
                    Media = new Media(libvlc, playPathUri, mediaOptions);
                    mediaPlayer.Media = Media;
                }
                else {
                    Media.AddOption(":sout=#file{dst=" + destination + ",channels=1,samplerate=16000}");
                }            
                mediaPlayer.Play();            
            }
            
    public void Get_20_seconds_audio_sample(){
        
            Get_sample(RadioURI,AudioSampleFileName);
            Wait_20_seconds();
            Stop();
    }
    
     public void Stop()
            {
                mediaPlayer.Stop();            
            }

The Problem is that radio streming ususally starts with a commercial that lasts about 25 seconds. Every sample plays the commercial. It seems that Stop() closes the stream until Play() is called again and it restart the stream. I tired to pause the audio but, well...it makes no much sense to pause and play.

I can accept to get the commercial only in the first sample but then I want the regular radio audio. Is there a way not to close the stream every time? I am not tied to VideoLan dll so I can start from scratch if you have a better way to do it.

Answer 1

Use Audio callbacks and save the audio stream yourself. Full sample:

class Program
    {
        // This sample shows you how you can use SetAudioFormatCallback and SetAudioCallbacks. It does two things:
        // 1) Play the sound from the specified video using NAudio
        // 2) Extract the sound into a file using NAudio

        static void Main(string[] args)
        {
            Core.Initialize();

            using var libVLC = new LibVLC(enableDebugLogs: true);
            using var media = new Media(libVLC,
                new Uri("http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4"),
                ":no-video");
            using var mediaPlayer = new MediaPlayer(media);

            using var outputDevice = new WaveOutEvent();
            var waveFormat = new WaveFormat(8000, 16, 1);
            var writer = new WaveFileWriter("sound.wav", waveFormat);
            var waveProvider = new BufferedWaveProvider(waveFormat);
            outputDevice.Init(waveProvider);

            mediaPlayer.SetAudioFormatCallback(AudioSetup, AudioCleanup);
            mediaPlayer.SetAudioCallbacks(PlayAudio, PauseAudio, ResumeAudio, FlushAudio, DrainAudio);

            mediaPlayer.Play();
            mediaPlayer.Time = 20_000; // Seek the video 20 seconds
            outputDevice.Play();

            Console.WriteLine("Press 'q' to quit. Press any other key to pause/play.");
            while (true)
            {
                if (Console.ReadKey().KeyChar == 'q')
                    break;

                if (mediaPlayer.IsPlaying)
                    mediaPlayer.Pause();
                else
                    mediaPlayer.Play();
            }

            void PlayAudio(IntPtr data, IntPtr samples, uint count, long pts)
            {
                int bytes = (int)count * 2; // (16 bit, 1 channel)
                var buffer = new byte[bytes];
                Marshal.Copy(samples, buffer, 0, bytes);

                waveProvider.AddSamples(buffer, 0, bytes);
                writer.Write(buffer, 0, bytes);
            }

            int AudioSetup(ref IntPtr opaque, ref IntPtr format, ref uint rate, ref uint channels)
            {
                channels = (uint)waveFormat.Channels;
                rate = (uint)waveFormat.SampleRate;
                return 0;
            }

            void DrainAudio(IntPtr data)
            {
                writer.Flush();
            }

            void FlushAudio(IntPtr data, long pts)
            {
                writer.Flush();
                waveProvider.ClearBuffer();
            }

            void ResumeAudio(IntPtr data, long pts)
            {
                outputDevice.Play();
            }

            void PauseAudio(IntPtr data, long pts)
            {
                outputDevice.Pause();
            }

            void AudioCleanup(IntPtr opaque) { }
        }
    }