mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-03 16:09:39 +00:00
872 lines
25 KiB
Markdown
872 lines
25 KiB
Markdown
# Basic Media Player
|
||
|
||
# Goal
|
||
|
||
This tutorial shows how to create a basic media player with
|
||
[Qt](http://qt-project.org/) and
|
||
[QtGStreamer](http://gstreamer.freedesktop.org/data/doc/gstreamer/head/qt-gstreamer/html/index.html).
|
||
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
|
||
|
||
**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
|
||
|
||
**main.cpp**
|
||
|
||
``` lang=c
|
||
#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
|
||
|
||
**mediaapp.h**
|
||
|
||
``` lang=c
|
||
#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
|
||
|
||
**mediaapp.cpp**
|
||
|
||
``` lang=c
|
||
#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
|
||
|
||
**player.h**
|
||
|
||
``` lang=c
|
||
#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
|
||
|
||
**player.cpp**
|
||
|
||
``` lang=c
|
||
#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("playbin").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**
|
||
|
||
``` lang=c
|
||
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](http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/gst-running.html)
|
||
section of the core reference manual for details.
|
||
|
||
Construction of the `MediaApp` (derived from
|
||
[`QApplication`](http://qt-project.org/doc/qt-5.0/qtwidgets/qapplication.html))
|
||
involves constructing the `Player` object and connecting its signals to
|
||
the UI:
|
||
|
||
**MediaApp::MediaApp()**
|
||
|
||
``` lang=c
|
||
//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()**
|
||
|
||
``` lang=c
|
||
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()**
|
||
|
||
``` lang=c
|
||
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("playbin").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`. `playbin` 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**
|
||
|
||
``` lang=c
|
||
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:
|
||
|
||
``` lang=c
|
||
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 `playbin` what to play by setting the `uri` property:
|
||
|
||
``` lang=c
|
||
m_pipeline->setProperty("uri", realUri);
|
||
```
|
||
|
||
## Starting Playback
|
||
|
||
After `Player::setUri()` is called, `MediaApp::openFile()` calls
|
||
`play()` on the `Player` object:
|
||
|
||
**Player::play()**
|
||
|
||
``` lang=c
|
||
void Player::play()
|
||
{
|
||
if (m_pipeline) {
|
||
m_pipeline->setState(QGst::StatePlaying);
|
||
}
|
||
}
|
||
```
|
||
|
||
The other state control methods are equally simple:
|
||
|
||
**Player state functions**
|
||
|
||
``` lang=c
|
||
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()**
|
||
|
||
``` lang=c
|
||
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()**
|
||
|
||
``` lang=c
|
||
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`](http://qt-project.org/doc/qt-5.0/qtcore/qtimer.html), the
|
||
`Player` emits the `positionChanged` signal at regular intervals for the
|
||
UI to handle:
|
||
|
||
**MediaApp::onPositionChanged()**
|
||
|
||
``` lang=c
|
||
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()**
|
||
|
||
``` lang=c
|
||
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\!
|