更改轨道 NAudio 后滑块不起作用

Question

我将滑块作为配乐的轨道栏 timeline.Soundtrack 使用 NAudion 从 Web 播放。使用 NAudio WPF example.I 的所有代码仅更改了可访问性 modifiers.First 当我开始播放第一首曲目时一切正常 good.But 如果我切换到下一首曲目，滑块仍在 start.And 仅更改如果我点击暂停然后播放。

完整理解：

第一首曲目 - 滑块工作并移动。

切换到下一首曲目 - 滑块在开头并且不移动。但它在按暂停后开始移动，然后按播放。它立即移动到当前正在播放的位置并继续正常运行。接下来的每首曲目也是如此。

PlayerUserControl 的 VM 代码：

public class AudioControlVM : ViewModelBase, IDisposable
    {
        private AudioModel _currentSong;

        public AudioModel CurrentSong { get { return _currentSong; } set { _currentSong = value; RaisePropertyChanged("CurrentSong"); } }

        private string inputPath, songName;
        private string defaultDecompressionFormat;
        public IWavePlayer wavePlayer { get; set; }
        private WaveStream reader;
        public RelayCommand PlayCommand { get; set; }
        public RelayCommand PauseCommand { get; set; }
        public RelayCommand StopCommand { get; set; }
        public DispatcherTimer timer = new DispatcherTimer();
        private double sliderPosition;
        private readonly ObservableCollection<string> inputPathHistory;
        private string lastPlayed;

        public AudioControlVM()
        {
            inputPathHistory = new ObservableCollection<string>();
            PlayCommand = new RelayCommand(() => Play());
            PauseCommand = new RelayCommand(() => Pause());
            StopCommand = new RelayCommand(Stop, () => !IsStopped);
            timer.Interval = TimeSpan.FromMilliseconds(500);
            timer.Tick += TimerOnTick;
        }

        public bool IsPlaying => wavePlayer != null && wavePlayer.PlaybackState == PlaybackState.Playing;

        public bool IsStopped => wavePlayer == null || wavePlayer.PlaybackState == PlaybackState.Stopped;


        public IEnumerable<string> InputPathHistory => inputPathHistory;

        const double SliderMax = 10.0;

        private void TimerOnTick(object sender, EventArgs eventArgs)
        {
            if (reader != null)
            {
                sliderPosition = reader.Position * SliderMax / reader.Length;
                RaisePropertyChanged("SliderPosition");
            }
        }

        public double SliderPosition
        {
            get => sliderPosition;
            set
            {
                if (sliderPosition != value)
                {
                    sliderPosition = value;
                    if (reader != null)
                    {
                        var pos = (long)(reader.Length * sliderPosition / SliderMax);
                        reader.Position = pos; // media foundation will worry about block align for us
                    }
                    RaisePropertyChanged("SliderPosition");
                }
            }
        }

        private bool TryOpenInputFile(string file)
        {
            bool isValid = false;
            try
            {
                using (var tempReader = new MediaFoundationReader(file))
                {
                    DefaultDecompressionFormat = tempReader.WaveFormat.ToString();
                    InputPath = file;
                    isValid = true;
                }
            }
            catch (Exception e)
            {

            }
            return isValid;
        }

        public string DefaultDecompressionFormat
        {
            get => defaultDecompressionFormat;
            set
            {
                defaultDecompressionFormat = value;
                RaisePropertyChanged("DefaultDecompressionFormat");
            }
        }

        public string SongName { get => songName; set
            {
                songName = value;
                RaisePropertyChanged("SongName");
            } }

        public string InputPath
        {
            get => inputPath;
            set
            {
                if (inputPath != value)
                {
                    inputPath = value;
                    AddToHistory(value);
                    RaisePropertyChanged("InputPath");
                }
            }
        }

        private void AddToHistory(string value)
        {
            if (!inputPathHistory.Contains(value))
            {
                inputPathHistory.Add(value);
            }
        }

        public void Stop()
        {
            if (wavePlayer != null)
            {
                wavePlayer.Stop();
            }
        }

        public void Pause()
        {
            if (wavePlayer != null)
            {
                wavePlayer.Pause();
                RaisePropertyChanged("IsPlaying");
                RaisePropertyChanged("IsStopped");
            }
        }

        public void Play()
        {
            if (String.IsNullOrEmpty(InputPath))
            {

                return;
            }
            if (wavePlayer == null)
            {
                CreatePlayer();
            }
            if (lastPlayed != inputPath && reader != null)
            {
                reader.Dispose();
                reader = null;
            }
            if (reader == null)
            {
                reader = new MediaFoundationReader(inputPath);
                lastPlayed = inputPath;
                wavePlayer.Init(reader);
            }
            wavePlayer.Play();
            RaisePropertyChanged("IsPlaying");
            RaisePropertyChanged("IsStopped");
            timer.Start();
        }

        private void CreatePlayer()
        {
            wavePlayer = new WaveOutEvent();
            wavePlayer.PlaybackStopped += WavePlayerOnPlaybackStopped;
            RaisePropertyChanged("wavePlayer");
        }

        private void WavePlayerOnPlaybackStopped(object sender, StoppedEventArgs stoppedEventArgs)
        {

            if (reader != null)
            {
                SliderPosition = 0;
                //reader.Position = 0;
                timer.Stop();
            }
            if (stoppedEventArgs.Exception != null)
            {

            }
            RaisePropertyChanged("IsPlaying");
            RaisePropertyChanged("IsStopped");
        }

        public void PlayFromUrl(string url, string songname)
        {
            Stop();
            inputPath = url;
            SongName = songname;
            Play();
        }

        public void Dispose()
        {
            wavePlayer?.Dispose();
            reader?.Dispose();
        }
    }

XAML 玩家：

    <Grid>
        <StackPanel Orientation="Horizontal">
        <Button Content="Play" Command="{Binding PlayCommand}" VerticalAlignment="Center" Width="75" />
        <Button Content="Pause" Command="{Binding PauseCommand}" VerticalAlignment="Center" Width="75" />
        <Button Content="Stop" Command="{Binding PlayCommand}" VerticalAlignment="Center" Width="75" />

        <Slider VerticalAlignment="Center" Value="{Binding SliderPosition, Mode=TwoWay}" Maximum="10" Width="400" />
            <TextBlock Text="{Binding SongName, FallbackValue=Test}" Foreground="White"/>
        </StackPanel>
    </Grid>
</UserControl>

为新轨道发送数据的VM代码：

public class AudioModel
{
    public string Artist { get; set; }
    public string SongName { get; set; }
    public int Duration { get; set; }
    public string URL { get; set; }

    public RelayCommand PlayThisAudioCommand
    {
        get;
        private set;
    }

    public AudioModel()
    {
        PlayThisAudioCommand = new RelayCommand(() => PlayThis());
    }

    private void PlayThis()
    {
        if (URL != null)
        {
            TestVM.AudioConrol.PlayFromUrl(URL, SongName);
        }
        else;
    }
}

Answer 1

您的计时器似乎存在多线程问题。事件的顺序似乎是：

第一首曲目

PlayFromUrl() 调用 Play() 开始播放文件，启动计时器。
滑块按预期更新

第二首曲目

当您调用 PlayFromUrl() 时：
调用 Stop()（停止 wavePlayer，停止计时器）
调用 Play()（启动 wavePlayer，启动计时器）
Then wavePlayer.PlaybackStopped 事件被引发（由于您之前调用了 wavePlayer.Stop()），它调用 WavePlayerOnPlaybackStopped()，停止计时器。

这里的重点是调用 Play() 和 WavePlayerOnPlaybackStopped() 的顺序。很可能事件按上述顺序发生 - 因为 wavePlayer 在另一个线程上引发了 PlaybackStopped 事件。

简而言之 - WavePlayerOnPlaybackStopped() 正在停止 你的计时器 after Play() started 它，这就是您的滑块未更新的原因。按暂停然后播放将重新启动计时器，这就是滑块在暂停后开始更新的原因。

您可以通过暂时注释掉 WavePlayerOnPlaybackStopped() 中的代码来对此进行测试，这应该可以解决问题 - 尽管当曲目到达终点或停止时您的滑块不会重置为零。

注意：调用 wavePlayer.Stop() 和引发 wavePlayer.PlaybackStopped 事件之间出现延迟的原因是 nAudio 使用专用线程处理播放。当您调用 Stop() 时，它必须在实际停止之前完成对当前音频缓冲区的处理——这在大多数情况下会导致几毫秒的延迟。

您可以在 WaveOutEvent 的 DoPlayback 方法中看到这一点：https://github.com/naudio/NAudio/blob/master/NAudio/Wave/WaveOutputs/WaveOutEvent.cs#L147

更改轨道 NAudio 后滑块不起作用

Slider do not work after changing track NAudio

c#

wpf

mvvm

slider

naudio

第一首曲目

第二首曲目