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<QString> 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; /**< Next entry in list */
    char *psz_device; /**< Device identifier string */
    char *psz_description; /**< User-friendly device description */
    /* More fields may be added here in later versions */
} libvlc_audio_output_device_t;

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 <QtWidgets/QWidget>
#include "ui_showWidget.h"
#include <QMenu>
#include <QActionGroup>
#include <vlc/vlc.h>
#include <QDebug>
#include <QFileDialog>
#include <QThread>
#include <QMouseEvent>
#include <QKeyEvent>

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<float> m_lstRate;
    QList<QString> 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 <QTimer>
#include <QTime>

#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 << 2.0 << 1.5 << 1.25 << 1.0 << 0.75 << 0.5;

	ui.btnOpen->setFocusPolicy(Qt::NoFocus);
	ui.btnPlay->setFocusPolicy(Qt::NoFocus);
	ui.btnPause->setFocusPolicy(Qt::NoFocus);
	ui.btnStop->setFocusPolicy(Qt::NoFocus);
	ui.hSliderVolumn->setFocusPolicy(Qt::NoFocus);
	ui.cbxRate->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 < track_count; i++) 
	{
		libvlc_media_track_t* track = tracks[i];

		// 显示轨道信息
		printf("Track #%u: %s\n", i, track->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媒体播放器时间已更改";
		qint64 len = libvlc_media_player_get_time(w->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() << "VLC播放完毕.";
		break;
	case libvlc_MediaPlayerStopped:
		qDebug() << "VLC停止播放";
		break;
	case libvlc_MediaPlayerPlaying:
		qDebug() << "VLC开始播放";
		break;
	case libvlc_MediaPlayerPaused:
		qDebug() << "VLC暂停播放";
		break;
	}
}

更多参考：

libVLC 事件机制-CSDN博客

libVLC windows开发环境搭建-CSDN博客

libVLC 视频抓图_libvlc 截图-CSDN博客

libVLC 动态视频壁纸-CSDN博客

libVLC 设置滤镜-CSDN博客