26 KiB
Basic Media Player
This page last changed on May 24, 2013 by xartigas.
Goal
This tutorial shows how to create a basic media player with Qt and QtGStreamer. It assumes that you are already familiar with the basics of Qt and GStreamer. If not, please refer to the other tutorials in this documentation.
In particular, you will learn:
- How to create a basic pipeline
- How to create a video output
- Updating the GUI based on playback time
A media player with Qt
These files are located in the qt-gstreamer SDK's examples/
directory.
Due to the length of these samples, they are initially hidden. Click on each file to expand.
CMakeLists.txt
project(qtgst-example-player)
find_package(QtGStreamer REQUIRED)
# automoc is now a built-in tool since CMake 2.8.6.
if (${CMAKE_VERSION} VERSION_LESS "2.8.6")
find_package(Automoc4 REQUIRED)
else()
set(CMAKE_AUTOMOC TRUE)
macro(automoc4_add_executable)
add_executable(${ARGV})
endmacro()
endif()
include_directories(${QTGSTREAMER_INCLUDES} ${CMAKE_CURRENT_BINARY_DIR} ${QT_QTWIDGETS_INCLUDE_DIRS})
add_definitions(${QTGSTREAMER_DEFINITIONS})
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${QTGSTREAMER_FLAGS}")
set(player_SOURCES main.cpp player.cpp mediaapp.cpp)
automoc4_add_executable(player ${player_SOURCES})
target_link_libraries(player ${QTGSTREAMER_UI_LIBRARIES} ${QT_QTOPENGL_LIBRARIES} ${QT_QTWIDGETS_LIBRARIES})
main.cpp
#include "mediaapp.h"
#include <QtWidgets/QApplication>
#include <QGst/Init>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QGst::init(&argc, &argv);
MediaApp media;
media.show();
if (argc == 2) {
media.openFile(argv[1]);
}
return app.exec();
}
mediaapp.h
#ifndef MEDIAAPP_H
#define MEDIAAPP_H
#include <QtCore/QTimer>
#include <QtWidgets/QWidget>
#include <QtWidgets/QStyle>
class Player;
class QBoxLayout;
class QLabel;
class QSlider;
class QToolButton;
class QTimer;
class MediaApp : public QWidget
{
Q_OBJECT
public:
MediaApp(QWidget *parent = 0);
~MediaApp();
void openFile(const QString & fileName);
private Q_SLOTS:
void open();
void toggleFullScreen();
void onStateChanged();
void onPositionChanged();
void setPosition(int position);
void showControls(bool show = true);
void hideControls() { showControls(false); }
protected:
void mouseMoveEvent(QMouseEvent *event);
private:
QToolButton *initButton(QStyle::StandardPixmap icon, const QString & tip,
QObject *dstobj, const char *slot_method, QLayout *layout);
void createUI(QBoxLayout *appLayout);
QString m_baseDir;
Player *m_player;
QToolButton *m_openButton;
QToolButton *m_fullScreenButton;
QToolButton *m_playButton;
QToolButton *m_pauseButton;
QToolButton *m_stopButton;
QSlider *m_positionSlider;
QSlider *m_volumeSlider;
QLabel *m_positionLabel;
QLabel *m_volumeLabel;
QTimer m_fullScreenTimer;
};
#endif
mediaapp.cpp
#include "mediaapp.h"
#include "player.h"
#if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
#include <QtWidgets/QBoxLayout>
#include <QtWidgets/QFileDialog>
#include <QtWidgets/QToolButton>
#include <QtWidgets/QLabel>
#include <QtWidgets/QSlider>
#else
#include <QtGui/QBoxLayout>
#include <QtGui/QFileDialog>
#include <QtGui/QToolButton>
#include <QtGui/QLabel>
#include <QtGui/QSlider>
#include <QtGui/QMouseEvent>
#endif
MediaApp::MediaApp(QWidget *parent)
: QWidget(parent)
{
//create the player
m_player = new Player(this);
connect(m_player, SIGNAL(positionChanged()), this, SLOT(onPositionChanged()));
connect(m_player, SIGNAL(stateChanged()), this, SLOT(onStateChanged()));
//m_baseDir is used to remember the last directory that was used.
//defaults to the current working directory
m_baseDir = QLatin1String(".");
//this timer (re-)hides the controls after a few seconds when we are in fullscreen mode
m_fullScreenTimer.setSingleShot(true);
connect(&m_fullScreenTimer, SIGNAL(timeout()), this, SLOT(hideControls()));
//create the UI
QVBoxLayout *appLayout = new QVBoxLayout;
appLayout->setContentsMargins(0, 0, 0, 0);
createUI(appLayout);
setLayout(appLayout);
onStateChanged(); //set the controls to their default state
setWindowTitle(tr("QtGStreamer example player"));
resize(400, 400);
}
MediaApp::~MediaApp()
{
delete m_player;
}
void MediaApp::openFile(const QString & fileName)
{
m_baseDir = QFileInfo(fileName).path();
m_player->stop();
m_player->setUri(fileName);
m_player->play();
}
void MediaApp::open()
{
QString fileName = QFileDialog::getOpenFileName(this, tr("Open a Movie"), m_baseDir);
if (!fileName.isEmpty()) {
openFile(fileName);
}
}
void MediaApp::toggleFullScreen()
{
if (isFullScreen()) {
setMouseTracking(false);
m_player->setMouseTracking(false);
m_fullScreenTimer.stop();
showControls();
showNormal();
} else {
setMouseTracking(true);
m_player->setMouseTracking(true);
hideControls();
showFullScreen();
}
}
void MediaApp::onStateChanged()
{
QGst::State newState = m_player->state();
m_playButton->setEnabled(newState != QGst::StatePlaying);
m_pauseButton->setEnabled(newState == QGst::StatePlaying);
m_stopButton->setEnabled(newState != QGst::StateNull);
m_positionSlider->setEnabled(newState != QGst::StateNull);
m_volumeSlider->setEnabled(newState != QGst::StateNull);
m_volumeLabel->setEnabled(newState != QGst::StateNull);
m_volumeSlider->setValue(m_player->volume());
//if we are in Null state, call onPositionChanged() to restore
//the position of the slider and the text on the label
if (newState == QGst::StateNull) {
onPositionChanged();
}
}
/* Called when the positionChanged() is received from the player */
void MediaApp::onPositionChanged()
{
QTime length(0,0);
QTime curpos(0,0);
if (m_player->state() != QGst::StateReady &&
m_player->state() != QGst::StateNull)
{
length = m_player->length();
curpos = m_player->position();
}
m_positionLabel->setText(curpos.toString("hh:mm:ss.zzz")
+ "/" +
length.toString("hh:mm:ss.zzz"));
if (length != QTime(0,0)) {
m_positionSlider->setValue(curpos.msecsTo(QTime(0,0)) * 1000 / length.msecsTo(QTime(0,0)));
} else {
m_positionSlider->setValue(0);
}
if (curpos != QTime(0,0)) {
m_positionLabel->setEnabled(true);
m_positionSlider->setEnabled(true);
}
}
/* Called when the user changes the slider's position */
void MediaApp::setPosition(int value)
{
uint length = -m_player->length().msecsTo(QTime(0,0));
if (length != 0 && value > 0) {
QTime pos(0,0);
pos = pos.addMSecs(length * (value / 1000.0));
m_player->setPosition(pos);
}
}
void MediaApp::showControls(bool show)
{
m_openButton->setVisible(show);
m_playButton->setVisible(show);
m_pauseButton->setVisible(show);
m_stopButton->setVisible(show);
m_fullScreenButton->setVisible(show);
m_positionSlider->setVisible(show);
m_volumeSlider->setVisible(show);
m_volumeLabel->setVisible(show);
m_positionLabel->setVisible(show);
}
void MediaApp::mouseMoveEvent(QMouseEvent *event)
{
Q_UNUSED(event);
if (isFullScreen()) {
showControls();
m_fullScreenTimer.start(3000); //re-hide controls after 3s
}
}
QToolButton *MediaApp::initButton(QStyle::StandardPixmap icon, const QString & tip,
QObject *dstobj, const char *slot_method, QLayout *layout)
{
QToolButton *button = new QToolButton;
button->setIcon(style()->standardIcon(icon));
button->setIconSize(QSize(36, 36));
button->setToolTip(tip);
connect(button, SIGNAL(clicked()), dstobj, slot_method);
layout->addWidget(button);
return button;
}
void MediaApp::createUI(QBoxLayout *appLayout)
{
appLayout->addWidget(m_player);
m_positionLabel = new QLabel();
m_positionSlider = new QSlider(Qt::Horizontal);
m_positionSlider->setTickPosition(QSlider::TicksBelow);
m_positionSlider->setTickInterval(10);
m_positionSlider->setMaximum(1000);
connect(m_positionSlider, SIGNAL(sliderMoved(int)), this, SLOT(setPosition(int)));
m_volumeSlider = new QSlider(Qt::Horizontal);
m_volumeSlider->setTickPosition(QSlider::TicksLeft);
m_volumeSlider->setTickInterval(2);
m_volumeSlider->setMaximum(10);
m_volumeSlider->setMaximumSize(64,32);
connect(m_volumeSlider, SIGNAL(sliderMoved(int)), m_player, SLOT(setVolume(int)));
QGridLayout *posLayout = new QGridLayout;
posLayout->addWidget(m_positionLabel, 1, 0);
posLayout->addWidget(m_positionSlider, 1, 1, 1, 2);
appLayout->addLayout(posLayout);
QHBoxLayout *btnLayout = new QHBoxLayout;
btnLayout->addStretch();
m_openButton = initButton(QStyle::SP_DialogOpenButton, tr("Open File"),
this, SLOT(open()), btnLayout);
m_playButton = initButton(QStyle::SP_MediaPlay, tr("Play"),
m_player, SLOT(play()), btnLayout);
m_pauseButton = initButton(QStyle::SP_MediaPause, tr("Pause"),
m_player, SLOT(pause()), btnLayout);
m_stopButton = initButton(QStyle::SP_MediaStop, tr("Stop"),
m_player, SLOT(stop()), btnLayout);
m_fullScreenButton = initButton(QStyle::SP_TitleBarMaxButton, tr("Fullscreen"),
this, SLOT(toggleFullScreen()), btnLayout);
btnLayout->addStretch();
m_volumeLabel = new QLabel();
m_volumeLabel->setPixmap(
style()->standardIcon(QStyle::SP_MediaVolume).pixmap(QSize(32, 32),
QIcon::Normal, QIcon::On));
btnLayout->addWidget(m_volumeLabel);
btnLayout->addWidget(m_volumeSlider);
appLayout->addLayout(btnLayout);
}
#include "moc_mediaapp.cpp"
player.h
#ifndef PLAYER_H
#define PLAYER_H
#include <QtCore/QTimer>
#include <QtCore/QTime>
#include <QGst/Pipeline>
#include <QGst/Ui/VideoWidget>
class Player : public QGst::Ui::VideoWidget
{
Q_OBJECT
public:
Player(QWidget *parent = 0);
~Player();
void setUri(const QString &uri);
QTime position() const;
void setPosition(const QTime &pos);
int volume() const;
QTime length() const;
QGst::State state() const;
public Q_SLOTS:
void play();
void pause();
void stop();
void setVolume(int volume);
Q_SIGNALS:
void positionChanged();
void stateChanged();
private:
void onBusMessage(const QGst::MessagePtr &message);
void handlePipelineStateChange(const QGst::StateChangedMessagePtr &scm);
QGst::PipelinePtr m_pipeline;
QTimer m_positionTimer;
};
#endif //PLAYER_H
player.cpp
#include "player.h"
#include <QtCore/QDir>
#include <QtCore/QUrl>
#include <QGlib/Connect>
#include <QGlib/Error>
#include <QGst/Pipeline>
#include <QGst/ElementFactory>
#include <QGst/Bus>
#include <QGst/Message>
#include <QGst/Query>
#include <QGst/ClockTime>
#include <QGst/Event>
#include <QGst/StreamVolume>
Player::Player(QWidget *parent)
: QGst::Ui::VideoWidget(parent)
{
//this timer is used to tell the ui to change its position slider & label
//every 100 ms, but only when the pipeline is playing
connect(&m_positionTimer, SIGNAL(timeout()), this, SIGNAL(positionChanged()));
}
Player::~Player()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StateNull);
stopPipelineWatch();
}
}
void Player::setUri(const QString & uri)
{
QString realUri = uri;
//if uri is not a real uri, assume it is a file path
if (realUri.indexOf("://") < 0) {
realUri = QUrl::fromLocalFile(realUri).toEncoded();
}
if (!m_pipeline) {
m_pipeline = QGst::ElementFactory::make("playbin2").dynamicCast<QGst::Pipeline>();
if (m_pipeline) {
//let the video widget watch the pipeline for new video sinks
watchPipeline(m_pipeline);
//watch the bus for messages
QGst::BusPtr bus = m_pipeline->bus();
bus->addSignalWatch();
QGlib::connect(bus, "message", this, &Player::onBusMessage);
} else {
qCritical() << "Failed to create the pipeline";
}
}
if (m_pipeline) {
m_pipeline->setProperty("uri", realUri);
}
}
QTime Player::position() const
{
if (m_pipeline) {
//here we query the pipeline about its position
//and we request that the result is returned in time format
QGst::PositionQueryPtr query = QGst::PositionQuery::create(QGst::FormatTime);
m_pipeline->query(query);
return QGst::ClockTime(query->position()).toTime();
} else {
return QTime(0,0);
}
}
void Player::setPosition(const QTime & pos)
{
QGst::SeekEventPtr evt = QGst::SeekEvent::create(
1.0, QGst::FormatTime, QGst::SeekFlagFlush,
QGst::SeekTypeSet, QGst::ClockTime::fromTime(pos),
QGst::SeekTypeNone, QGst::ClockTime::None
);
m_pipeline->sendEvent(evt);
}
int Player::volume() const
{
if (m_pipeline) {
QGst::StreamVolumePtr svp =
m_pipeline.dynamicCast<QGst::StreamVolume>();
if (svp) {
return svp->volume(QGst::StreamVolumeFormatCubic) * 10;
}
}
return 0;
}
void Player::setVolume(int volume)
{
if (m_pipeline) {
QGst::StreamVolumePtr svp =
m_pipeline.dynamicCast<QGst::StreamVolume>();
if(svp) {
svp->setVolume((double)volume / 10, QGst::StreamVolumeFormatCubic);
}
}
}
QTime Player::length() const
{
if (m_pipeline) {
//here we query the pipeline about the content's duration
//and we request that the result is returned in time format
QGst::DurationQueryPtr query = QGst::DurationQuery::create(QGst::FormatTime);
m_pipeline->query(query);
return QGst::ClockTime(query->duration()).toTime();
} else {
return QTime(0,0);
}
}
QGst::State Player::state() const
{
return m_pipeline ? m_pipeline->currentState() : QGst::StateNull;
}
void Player::play()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StatePlaying);
}
}
void Player::pause()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StatePaused);
}
}
void Player::stop()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StateNull);
//once the pipeline stops, the bus is flushed so we will
//not receive any StateChangedMessage about this.
//so, to inform the ui, we have to emit this signal manually.
Q_EMIT stateChanged();
}
}
void Player::onBusMessage(const QGst::MessagePtr & message)
{
switch (message->type()) {
case QGst::MessageEos: //End of stream. We reached the end of the file.
stop();
break;
case QGst::MessageError: //Some error occurred.
qCritical() << message.staticCast<QGst::ErrorMessage>()->error();
stop();
break;
case QGst::MessageStateChanged: //The element in message->source() has changed state
if (message->source() == m_pipeline) {
handlePipelineStateChange(message.staticCast<QGst::StateChangedMessage>());
}
break;
default:
break;
}
}
void Player::handlePipelineStateChange(const QGst::StateChangedMessagePtr & scm)
{
switch (scm->newState()) {
case QGst::StatePlaying:
//start the timer when the pipeline starts playing
m_positionTimer.start(100);
break;
case QGst::StatePaused:
//stop the timer when the pipeline pauses
if(scm->oldState() == QGst::StatePlaying) {
m_positionTimer.stop();
}
break;
default:
break;
}
Q_EMIT stateChanged();
}
#include "moc_player.cpp"
Walkthrough
Setting up GStreamer
We begin by looking at main()
:
main.cpp
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QGst::init(&argc, &argv);
MediaApp media;
media.show();
if (argc == 2) {
media.openFile(argv[1]);
}
return app.exec();
}
We first initialize QtGStreamer by calling QGst::init()
, passing
argc
and argv
. Internally, this ensures that the GLib type system
and GStreamer plugin registry is configured and initialized, along with
handling helpful environment variables such as GST_DEBUG
and common
command line options. Please see the Running GStreamer
Applications
section of the core reference manual for details.
Construction of the MediaApp
(derived from
QApplication
)
involves constructing the Player
object and connecting its signals to
the UI:
MediaApp::MediaApp()
//create the player
m_player = new Player(this);
connect(m_player, SIGNAL(positionChanged()), this, SLOT(onPositionChanged()));
connect(m_player, SIGNAL(stateChanged()), this, SLOT(onStateChanged()));
Next, we instruct the MediaApp
to open the file given on the command
line, if any:
MediaApp::openFile()
void MediaApp::openFile(const QString & fileName)
{
m_baseDir = QFileInfo(fileName).path();
m_player->stop();
m_player->setUri(fileName);
m_player->play();
}
This in turn instructs the Player
to construct our GStreamer pipeline:
Player::setUri()
void Player::setUri(const QString & uri)
{
QString realUri = uri;
//if uri is not a real uri, assume it is a file path
if (realUri.indexOf("://") < 0) {
realUri = QUrl::fromLocalFile(realUri).toEncoded();
}
if (!m_pipeline) {
m_pipeline = QGst::ElementFactory::make("playbin2").dynamicCast<QGst::Pipeline>();
if (m_pipeline) {
//let the video widget watch the pipeline for new video sinks
watchPipeline(m_pipeline);
//watch the bus for messages
QGst::BusPtr bus = m_pipeline->bus();
bus->addSignalWatch();
QGlib::connect(bus, "message", this, &Player::onBusMessage);
} else {
qCritical() << "Failed to create the pipeline";
}
}
if (m_pipeline) {
m_pipeline->setProperty("uri", realUri);
}
}
Here, we first ensure that the pipeline will receive a proper URI. If
Player::setUri()
is called with /home/user/some/file.mp3
, the path
is modified to file:///home/user/some/file.mp3
. playbin2
only
accepts complete URIs.
The pipeline is created via QGst::ElementFactory::make()
. The
Player
object inherits from the QGst::Ui::VideoWidget
class, which
includes a function to watch for the prepare-xwindow-id
message, which
associates the underlying video sink with a Qt widget used for
rendering. For clarity, here is a portion of the implementation:
prepare-xwindow-id handling
QGlib::connect(pipeline->bus(), "sync-message",
this, &PipelineWatch::onBusSyncMessage);
...
void PipelineWatch::onBusSyncMessage(const MessagePtr & msg)
{
...
if (msg->internalStructure()->name() == QLatin1String("prepare-xwindow-id")) {
XOverlayPtr overlay = msg->source().dynamicCast<XOverlay>();
m_renderer->setVideoSink(overlay);
}
Once the pipeline is created, we connect to the bus' message signal (via
QGlib::connect()
) to dispatch state change signals:
void Player::onBusMessage(const QGst::MessagePtr & message)
{
switch (message->type()) {
case QGst::MessageEos: //End of stream. We reached the end of the file.
stop();
break;
case QGst::MessageError: //Some error occurred.
qCritical() << message.staticCast<QGst::ErrorMessage>()->error();
stop();
break;
case QGst::MessageStateChanged: //The element in message->source() has changed state
if (message->source() == m_pipeline) {
handlePipelineStateChange(message.staticCast<QGst::StateChangedMessage>());
}
break;
default:
break;
}
}
void Player::handlePipelineStateChange(const QGst::StateChangedMessagePtr & scm)
{
switch (scm->newState()) {
case QGst::StatePlaying:
//start the timer when the pipeline starts playing
m_positionTimer.start(100);
break;
case QGst::StatePaused:
//stop the timer when the pipeline pauses
if(scm->oldState() == QGst::StatePlaying) {
m_positionTimer.stop();
}
break;
default:
break;
}
Q_EMIT stateChanged();
}
Finally, we tell playbin2
what to play by setting the uri
property:
m_pipeline->setProperty("uri", realUri);
Starting Playback
After Player::setUri()
is called, MediaApp::openFile()
calls
play()
on the Player
object:
Player::play()
void Player::play()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StatePlaying);
}
}
The other state control methods are equally simple:
Player state functions
void Player::pause()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StatePaused);
}
}
void Player::stop()
{
if (m_pipeline) {
m_pipeline->setState(QGst::StateNull);
//once the pipeline stops, the bus is flushed so we will
//not receive any StateChangedMessage about this.
//so, to inform the ui, we have to emit this signal manually.
Q_EMIT stateChanged();
}
}
Once the pipeline has entered the playing state, a state change message
is emitted on the GStreamer bus which gets picked up by the Player
:
Player::onBusMessage()
void Player::onBusMessage(const QGst::MessagePtr & message)
{
switch (message->type()) {
case QGst::MessageEos: //End of stream. We reached the end of the file.
stop();
break;
case QGst::MessageError: //Some error occurred.
qCritical() << message.staticCast<QGst::ErrorMessage>()->error();
stop();
break;
case QGst::MessageStateChanged: //The element in message->source() has changed state
if (message->source() == m_pipeline) {
handlePipelineStateChange(message.staticCast<QGst::StateChangedMessage>());
}
break;
default:
break;
}
}
The stateChanged
signal we connected to earlier is emitted and
handled:
MediaApp::onStateChanged()
void MediaApp::onStateChanged()
{
QGst::State newState = m_player->state();
m_playButton->setEnabled(newState != QGst::StatePlaying);
m_pauseButton->setEnabled(newState == QGst::StatePlaying);
m_stopButton->setEnabled(newState != QGst::StateNull);
m_positionSlider->setEnabled(newState != QGst::StateNull);
m_volumeSlider->setEnabled(newState != QGst::StateNull);
m_volumeLabel->setEnabled(newState != QGst::StateNull);
m_volumeSlider->setValue(m_player->volume());
//if we are in Null state, call onPositionChanged() to restore
//the position of the slider and the text on the label
if (newState == QGst::StateNull) {
onPositionChanged();
}
}
This updates the UI to reflect the current state of the player's pipeline.
Driven by a
QTimer
, the
Player
emits the positionChanged
signal at regular intervals for the
UI to handle:
MediaApp::onPositionChanged()
void MediaApp::onPositionChanged()
{
QTime length(0,0);
QTime curpos(0,0);
if (m_player->state() != QGst::StateReady &&
m_player->state() != QGst::StateNull)
{
length = m_player->length();
curpos = m_player->position();
}
m_positionLabel->setText(curpos.toString("hh:mm:ss.zzz")
+ "/" +
length.toString("hh:mm:ss.zzz"));
if (length != QTime(0,0)) {
m_positionSlider->setValue(curpos.msecsTo(QTime(0,0)) * 1000 / length.msecsTo(QTime(0,0)));
} else {
m_positionSlider->setValue(0);
}
if (curpos != QTime(0,0)) {
m_positionLabel->setEnabled(true);
m_positionSlider->setEnabled(true);
}
}
The MediaApp
queries the pipeline via the Player
's
position()
method, which submits a position query. This is analogous
to gst_element_query_position()
:
Player::position()
QTime Player::position() const
{
if (m_pipeline) {
//here we query the pipeline about its position
//and we request that the result is returned in time format
QGst::PositionQueryPtr query = QGst::PositionQuery::create(QGst::FormatTime);
m_pipeline->query(query);
return QGst::ClockTime(query->position()).toTime();
} else {
return QTime(0,0);
}
}
Due to the way Qt handles signals that cross threads, there is no need to worry about calling UI functions from outside the UI thread in this example.
Conclusion
This tutorial has shown:
- How to create a basic pipeline
- How to create a video output
- Updating the GUI based on playback time
It has been a pleasure having you here, and see you soon!
Document generated by Confluence on Oct 08, 2015 10:27