libVLC 音频输出设备切换

libvlc_audio_output_list_get和libvlc_audio_output_device_list_get是libVLC 库中用于处理音频输出的两个函数。

• libvlc_audio_output_list_get函数用于获取可用的音频输出模块列表。这个列表通常包括不同的音频输出方式，例如 Pulseaudio、ALSA 等。通过这个函数，可以了解有哪些音频输出模块可供使用。
• libvlc_audio_output_device_list_get函数则是用于获取特定音频输出模块下的音频输出设备列表。这个函数通常在选择了特定的音频输出模块后使用，用于列出该模块下的具体设备，例如特定的声卡或硬件设备。

  libvlc_audio_output_list_get用于获取音频输出模块的列表。

  libvlc_audio_output_device_list_get用于获取特定模块下的音频输出设备的列表。

  在实际应用中，需要先使用 libvlc_audio_output_list_get获取音频输出模块，然后针对每个模块使用 libvlc_audio_output_device_list_get获取其下的设备列表，以便于用户选择和配置。

  以下是VLC播放器中使用的截图界面，我们仿照这个做一个界面。 

  

  以下是效果图。

  

  首先程序运行起来获取音频设备列表，创建菜单项。

      QList m_lstAudioDevice;	
      m_lstAudioDevice.clear();
  	libvlc_audio_output_device_t *pDevList = nullptr;
  	libvlc_audio_output_t *pOutputList = libvlc_audio_output_list_get(vlc_base);
  	while (pOutputList)
  	{
  		//获取设备
  		pDevList = libvlc_audio_output_device_list_get(vlc_base, pOutputList->psz_name);
  		while (pDevList)
  		{
  			// 找到我想要的那个设备，跳出循环，这里使用i控制，我知道我想要的设备位置
  			if (strcmp(pOutputList->psz_name, "mmdevice") == 0)
  			{
  				QString des = QString::fromStdString(std::string(pDevList->psz_description, strlen(pDevList->psz_description)));
  				m_lstAudioDevice.append(des);
  				QAction *action = m_deviceMenu->addAction(des);
  				action->setData(pDevList->psz_device);
  				m_group->addAction(action);
  			}
  			pDevList = pDevList->p_next;
  		}
  		pOutputList = pOutputList->p_next;
  	}

  libvlc_audio_output_list_get获取音频输出模块的列表。

  libvlc_audio_output_device_list_get获取特定模块下的音频输出设备的列表。

  这里我找到名为"mmdevice"模块下的所有音频输出设备，存储到一个QList中。

  setData设置设备标识符字符串。方便我们在切换的时候使用这个标识符。

  typedef struct libvlc_audio_output_device_t
  {
      struct libvlc_audio_output_device_t *p_next; /** 
  因为在libvlc_audio_output_device_set这个接口中，参数device_id就是上面的设备标识符。
   
  LIBVLC_API void libvlc_audio_output_device_set( libvlc_media_player_t *mp,
                                                  const char *module,
                                                  const char *device_id );
   
  如果需要切换音频输出模块，调用libvlc_audio_output_set。
   
  /**
   * Selects an audio output module.
   * \note Any change will take be effect only after playback is stopped and
   * restarted. Audio output cannot be changed while playing.
   *
   * \param p_mi media player
   * \param psz_name name of audio output,
   *               use psz_name of \see libvlc_audio_output_t
   * \return 0 if function succeeded, -1 on error
   */
  LIBVLC_API int libvlc_audio_output_set( libvlc_media_player_t *p_mi,
                                          const char *psz_name );
   
  官方的解释是，你需要先停止播放，设置新的音频输出设备，然后重新开始播放，以便新的设置生效。 
   
  示例代码：
   
  	libvlc_media_player_stop(vlc_mediaPlayer);
  	//设置输出waveout
  	int ret = libvlc_audio_output_set(vlc_mediaPlayer, "mmdevice");
  	//指定设备输出pDevList->psz_device
  	libvlc_audio_output_device_set(vlc_mediaPlayer, NULL, txt.toStdString().c_str());
  	libvlc_media_player_play(vlc_mediaPlayer);
   
  如果需要切换音频输出设备，设备在同一模块下，就不需要调用libvlc_audio_output_set，直接调用libvlc_audio_output_device_set，这个是不需要停止播放，再重新播放。
   
   * \param mp media player
   * \param module If NULL, current audio output module.
   *               if non-NULL, name of audio output module
                   (\see libvlc_audio_output_t)
   * \param device_id device identifier string
   * \return Nothing. Errors are ignored (this is a design bug).
   */
  LIBVLC_API void libvlc_audio_output_device_set( libvlc_media_player_t *mp,
   const char *module,
   const char *device_id );
   
  官方解释，参数module插入参数NULL，就使用当前的音频输出模块。 
   
  示例代码：
   
  void showWidget::slotActionTriggered(QAction *action)
  {
  	if (!vlc_mediaPlayer)
  		return;
  	
  	QString txt = action->data().toString();
  	//指定设备输出pDevList->psz_device
  	libvlc_audio_output_device_set(vlc_mediaPlayer, NULL, txt.toStdString().c_str());
  }
   
  完整源码：本示例演示同一模块下，输出设备的切换。
   
  #pragma once
  #include 
  #include "ui_showWidget.h"
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 
  enum Rate
  {
  	Rate2X,
  	Rate1_5X,
  	Rate1_25X,
  	Rate1_0X,
  	Rate0_75X,
  	Rate0_5X
  };
  class showWidget : public QWidget
  {
      Q_OBJECT
  public:
      showWidget(QWidget *parent = nullptr);
      ~showWidget();
  private slots:
  	void slotOpenFile();
  	void slotPlay();
  	void slotPause();
  	void slotStop();
  	void slotValueChanged(int value);
  	void slotCurrentIndexChanged(int index);
  	void slotActionTriggered(QAction *action);
  protected:
  	virtual void mousePressEvent(QMouseEvent *event);
  private:
  	//事件处理回调
  	static void vlcEvents(const libvlc_event_t *ev, void *param);
  private:
      Ui::showWidgetClass ui;
  private:
  	libvlc_instance_t *vlc_base = nullptr;
  	libvlc_media_t *vlc_media = nullptr;
  	libvlc_media_player_t *vlc_mediaPlayer = nullptr;
  	QList m_lstRate;
      QList m_lstAudioDevice;
  	QMenu *m_menu = nullptr;
  	QMenu *m_deviceMenu = nullptr;
  	QAction *m_actionAudioDev = nullptr;	//音频设备
  	QActionGroup *m_group = nullptr;
  };
   
  cpp文件。 
   
  #include "showWidget.h"
  #include 
  #include 
  #pragma execution_character_set("utf-8")
  showWidget::showWidget(QWidget *parent)
      : QWidget(parent)
  {
      ui.setupUi(this);
  	this->setWindowTitle("视频播放器");
  	m_menu = new QMenu(this);
  	m_actionAudioDev = m_menu->addAction("音频设备");
  	m_deviceMenu = new QMenu(this);
  	m_actionAudioDev->setMenu(m_deviceMenu);
  	m_group = new QActionGroup(this);
  	connect(m_group, &QActionGroup::triggered, this, &showWidget::slotActionTriggered);
  	vlc_base = libvlc_new(0, NULL);
  	m_lstAudioDevice.clear();
  	libvlc_audio_output_device_t *pDevList = nullptr;
  	libvlc_audio_output_t *pOutputList = libvlc_audio_output_list_get(vlc_base);
  	while (pOutputList)
  	{
  		//获取设备
  		pDevList = libvlc_audio_output_device_list_get(vlc_base, pOutputList->psz_name);
  		while (pDevList)
  		{
  			// 找到我想要的那个设备，跳出循环，这里使用i控制，我知道我想要的设备位置
  			if (strcmp(pOutputList->psz_name, "mmdevice") == 0)
  			{
  				QString des = QString::fromStdString(std::string(pDevList->psz_description, strlen(pDevList->psz_description)));
  				m_lstAudioDevice.append(des);
  				QAction *action = m_deviceMenu->addAction(des);
  				action->setData(pDevList->psz_device);
  				m_group->addAction(action);
  			}
  			pDevList = pDevList->p_next;
  		}
  		pOutputList = pOutputList->p_next;
  	}
  	ui.cbxRate->setCurrentIndex(Rate1_0X);
  	m_lstRate setFocusPolicy(Qt::NoFocus);
  	connect(ui.btnOpen, &QPushButton::clicked, this, &showWidget::slotOpenFile);
  	connect(ui.btnPlay, &QPushButton::clicked, this, &showWidget::slotPlay);
  	connect(ui.btnPause, &QPushButton::clicked, this, &showWidget::slotPause);
  	connect(ui.btnStop, &QPushButton::clicked, this, &showWidget::slotStop);
  	connect(ui.hSliderVolumn, &QSlider::valueChanged, this, &showWidget::slotValueChanged);
  	connect(ui.cbxRate,SIGNAL(currentIndexChanged(int)), this, SLOT(slotCurrentIndexChanged(int)));
  }
  showWidget::~showWidget()
  {
  	libvlc_release(vlc_base); //减少libvlc实例的引用计数，并销毁
  }
  void showWidget::slotOpenFile()
  {
  	/*选择文件*/
  	QString filename = QFileDialog::getOpenFileName(this, "选择打开的文件", "D:/", tr("*.*"));
  	std::replace(filename.begin(), filename.end(), QChar('/'), QChar('\\'));
  	
  	vlc_media = libvlc_media_new_path(vlc_base, filename.toUtf8().data());
  	if (!vlc_media) {
  		return;
  	}
  	// 创建libvlc实例和媒体播放器
  	vlc_mediaPlayer = libvlc_media_player_new_from_media(vlc_media);
  	if (!vlc_mediaPlayer) {
  		return;
  	}
  	//libvlc_media_add_option(vlc_media, "--video-filter=transform");
  	//libvlc_media_add_option(vlc_media, "---transform-type=270");
  	
  	// 等待元数据加载完成
  	libvlc_media_parse(vlc_media);
  	libvlc_video_set_mouse_input(vlc_mediaPlayer, 0);
  	libvlc_video_set_key_input(vlc_mediaPlayer, 0);
  	// 获取各种元数据
  	const char *title = libvlc_media_get_meta(vlc_media, libvlc_meta_Title);
  	const char *artist = libvlc_media_get_meta(vlc_media, libvlc_meta_Artist);
  	const char *album = libvlc_media_get_meta(vlc_media, libvlc_meta_Album);
  	const char *url = libvlc_media_get_meta(vlc_media, libvlc_meta_URL);
  	const char *date = libvlc_media_get_meta(vlc_media, libvlc_meta_Date);
  	const char *lang = libvlc_media_get_meta(vlc_media, libvlc_meta_Language);
  	int duration = libvlc_media_get_duration(vlc_media);  // 获取时长（单位：毫秒）
  	qDebug("Title: %s", title ? title : "N/A");
  	qDebug("Artist: %s", artist ? artist : "N/A");
  	qDebug("Album: %s", album ? album : "N/A");
  	qDebug("Duration: %d ms", duration);
  	qDebug("url: %s", url ? url : "N/A");
  	qDebug("date: %s", date ? date : "N/A");
  	qDebug("lang: %s", lang ? lang : "N/A");
  	
  	libvlc_media_track_t **tracks;
  	int track_count = libvlc_media_tracks_get(vlc_media,&tracks);
  	for (unsigned i = 0; i psz_description);
  		// 这里可以获取到每一个轨道的信息，比如轨道类型 track->i_type
  		// 可能是 libvlc_track_video, libvlc_track_audio 或者 libvlc_track_text (字幕)
  		if (track->i_type == libvlc_track_video) {
  			// 处理视频轨道信息
  			qDebug("width = %d",track->video->i_width);
  			qDebug("height = %d", track->video->i_height);
  			qDebug("rate_num = %d", track->video->i_frame_rate_num);
  			qDebug("rate_den = %d", track->video->i_frame_rate_den);
  		}
  		else if (track->i_type == libvlc_track_audio) {
  			// 处理音频轨道信息
  			qDebug("channels = %d", track->audio->i_channels);
  			qDebug("rate = %d", track->audio->i_rate);
  		}
  		else if (track->i_type == libvlc_track_text) {
  			// 处理字幕轨道信息
  		}
  	}
  	//获取事件管理器
  	libvlc_event_manager_t *em = libvlc_media_player_event_manager(vlc_mediaPlayer);
  	// 注册事件监听器
  	libvlc_event_attach(em, libvlc_MediaPlayerTimeChanged, vlcEvents, this);
  	libvlc_event_attach(em, libvlc_MediaPlayerEndReached, vlcEvents, this);
  	libvlc_event_attach(em, libvlc_MediaPlayerStopped, vlcEvents, this);
  	libvlc_event_attach(em, libvlc_MediaPlayerPlaying, vlcEvents, this);
  	libvlc_event_attach(em, libvlc_MediaPlayerPaused, vlcEvents, this);
  	libvlc_media_player_set_hwnd(vlc_mediaPlayer, (void *)ui.widgetShow->winId());
  	libvlc_video_set_adjust_int(vlc_mediaPlayer, libvlc_adjust_Enable, 1);
  	QTimer::singleShot(1000, this, &showWidget::slotPlay);
  	libvlc_video_filter_list_get(vlc_base);
  	
  }
  void showWidget::slotPlay()
  {
  	if (vlc_mediaPlayer)
  	{
  		libvlc_media_player_play(vlc_mediaPlayer);
  	}
  	
  }
  void showWidget::slotPause()
  {
  	if (vlc_mediaPlayer)
  		libvlc_media_player_pause(vlc_mediaPlayer);
  }
  void showWidget::slotStop()
  {
  	if (vlc_mediaPlayer)
  		libvlc_media_player_stop(vlc_mediaPlayer);
  }
  void showWidget::slotValueChanged(int value)
  {
  	if (vlc_mediaPlayer)
  		libvlc_audio_set_volume(vlc_mediaPlayer, value);
  }
  void showWidget::slotCurrentIndexChanged(int index)
  {
  	if (vlc_mediaPlayer)
  		libvlc_media_player_set_rate(vlc_mediaPlayer, m_lstRate[index]);
  }
  void showWidget::slotActionTriggered(QAction *action)
  {
  	if (!vlc_mediaPlayer)
  		return;
  	
  	QString txt = action->data().toString();
  	//指定设备输出pDevList->psz_device
  	libvlc_audio_output_device_set(vlc_mediaPlayer, NULL, txt.toStdString().c_str());
  }
  void showWidget::mousePressEvent(QMouseEvent *event)
  {
  	switch (event->button())
  	{
  	case Qt::RightButton:
  		//this->setWindowState(Qt::WindowMinimized);
  		m_menu->exec(event->globalPos());
  		break;
  	default:
  		QWidget::mousePressEvent(event);
  	}
  }
  //事件回调
  void showWidget::vlcEvents(const libvlc_event_t *ev, void *param)
  {
  	showWidget *w = (showWidget*)param;
  	//处理不同的事件
  	switch (ev->type) {
  	case libvlc_MediaPlayerTimeChanged:
  	{
  		//qDebug() vlc_mediaPlayer);
  		libvlc_time_t lenSec = len / 1000;
  		libvlc_time_t totalLen = libvlc_media_player_get_length(w->vlc_mediaPlayer);
  		libvlc_time_t totalLenSec = totalLen / 1000;
  		int thh, tmm, tss;
  		thh = lenSec / 3600;
  		tmm = (lenSec % 3600) / 60;
  		tss = (lenSec % 60);
  		QTime time(thh, tmm, tss);
  		w->ui.lbCurTime->setText(time.toString("hh:mm:ss"));
  		thh = totalLenSec / 3600;
  		tmm = (totalLenSec % 3600) / 60;
  		tss = (totalLenSec % 60);
  		QTime TotalTime(thh, tmm, tss);
  		w->ui.lbTotalTime->setText(TotalTime.toString("hh:mm:ss"));
  		double pos = (double)lenSec / totalLenSec * 100;
  		w->ui.horizontalSlider->setValue(pos);
  	}
  		break;
  	case libvlc_MediaPlayerEndReached:
  		qDebug()