GStreamer基礎教程11 - 與QT集成

摘要

　　一般咱們的播放引擎須要和GUI進行集成，在使用GStreamer時，GStreamre會負責媒體的播放及控制，GUI會負責處理用戶的交互操做以及建立顯示的窗口。本例中咱們將結合QT介紹如何指定GStreamer將視頻輸出到指定窗口，以及如何利用GStreamer上報的信息去更新GUI。

 

與GUI集成

咱們知道與GUI集成有兩個方面須要注意：

• 顯示窗口的管理。

　　因爲顯示窗口一般由GUI框架建立，因此咱們須要將具體的窗口信息告訴GStreamer。因爲各個平臺使用不一樣的方式傳遞窗口句柄，GStreamer提供了一個抽象接口（GstVideoOverlay），用於屏蔽平臺的差別，咱們能夠直接將GUI建立的窗口ID傳遞給GStreamer。

• GUI界面的更新

　　大多數GUI框架都須要在主線程中去作UI的刷新操做，但GStreamer內部可能會建立多個線程，這就須要經過GstBus及GUI自帶的通訊機制將全部GStreamer產生的消息傳遞到GUI主線程，再由GUI主線程對界面進行刷新。

 

　　下面咱們將以QT爲例來了解如何處理GStreamer與GUI框架的集成。

示例代碼

qtoverlay.h

#ifndef _QTOVERLAY_
#define _QTOVERLAY_

#include <gst/gst.h>

#include <QWidget>
#include <QPushButton>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QSlider>
#include <QTimer>

class PlayerWindow : public QWidget
{
    Q_OBJECT
public:
  PlayerWindow(GstElement *p);

  WId getVideoWId() const ;
  static gboolean postGstMessage(GstBus * bus, GstMessage * message, gpointer user_data);

private slots:
  void onPlayClicked() ;
  void onPauseClicked() ;
  void onStopClicked() ;
  void onAlbumAvaiable(const QString &album);
  void onState(GstState st);
  void refreshSlider();
  void onSeek();
  void onEos();

signals:
  void sigAlbum(const QString &album);
  void sigState(GstState st);
  void sigEos();
  
private:
  GstElement *pipeline;
  QPushButton *playBt;
  QPushButton *pauseBt;
  QPushButton *stopBt;
  QWidget *videoWindow;
  QSlider *slider;
  QHBoxLayout *buttonLayout;
  QVBoxLayout *playerLayout;
  QTimer *timer;

  GstState state;
  gint64 totalDuration;
};

#endif

View Code

qtoverlay.cpp

#include <gst/video/videooverlay.h>
#include <QApplication>
#include "qtoverlay.h"

PlayerWindow::PlayerWindow(GstElement *p)
    :pipeline(p)
    ,state(GST_STATE_NULL)
    ,totalDuration(GST_CLOCK_TIME_NONE)
{
    playBt = new QPushButton("Play");
    pauseBt = new QPushButton("Pause");
    stopBt = new QPushButton("Stop");
    videoWindow = new QWidget();
    slider = new QSlider(Qt::Horizontal);
    timer = new QTimer();

    connect(playBt, SIGNAL(clicked()), this, SLOT(onPlayClicked()));
    connect(pauseBt, SIGNAL(clicked()), this, SLOT(onPauseClicked()));
    connect(stopBt, SIGNAL(clicked()), this, SLOT(onStopClicked()));
    connect(slider, SIGNAL(sliderReleased()), this, SLOT(onSeek()));

    buttonLayout = new QHBoxLayout;
    buttonLayout->addWidget(playBt);
    buttonLayout->addWidget(pauseBt);
    buttonLayout->addWidget(stopBt);
    buttonLayout->addWidget(slider);

    playerLayout = new QVBoxLayout;
    playerLayout->addWidget(videoWindow);
    playerLayout->addLayout(buttonLayout);

    this->setLayout(playerLayout);

    connect(timer, SIGNAL(timeout()), this, SLOT(refreshSlider()));
    connect(this, SIGNAL(sigAlbum(QString)), this, SLOT(onAlbumAvaiable(QString)));
    connect(this, SIGNAL(sigState(GstState)), this, SLOT(onState(GstState)));
    connect(this, SIGNAL(sigEos()), this, SLOT(onEos()));
}

WId PlayerWindow::getVideoWId() const {
    return videoWindow->winId();
}

void PlayerWindow::onPlayClicked() {
    GstState st = GST_STATE_NULL;
    gst_element_get_state (pipeline, &st, NULL, GST_CLOCK_TIME_NONE);
    if (st < GST_STATE_PAUSED) {
        // Pipeline stopped, we need set overlay again
        GstElement *vsink = gst_element_factory_make ("ximagesink", "vsink");
        g_object_set(GST_OBJECT(pipeline), "video-sink", vsink, NULL);
        WId xwinid = getVideoWId();
        gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (vsink), xwinid);
    }
    gst_element_set_state (pipeline, GST_STATE_PLAYING);
}

void PlayerWindow::onPauseClicked() {
    gst_element_set_state (pipeline, GST_STATE_PAUSED);
}

void PlayerWindow::onStopClicked() {
    gst_element_set_state (pipeline, GST_STATE_NULL);
}

void PlayerWindow::onAlbumAvaiable(const QString &album) {
    setWindowTitle(album);
}

void PlayerWindow::onState(GstState st) {
    if (state != st) {
        state = st;
        if (state == GST_STATE_PLAYING){
            timer->start(1000);
        }
        if (state < GST_STATE_PAUSED){
            timer->stop();
        }
    }
}

void PlayerWindow::refreshSlider() {
    gint64 current = GST_CLOCK_TIME_NONE;
    if (state == GST_STATE_PLAYING) {
        if (!GST_CLOCK_TIME_IS_VALID(totalDuration)) {
            if (gst_element_query_duration (pipeline, GST_FORMAT_TIME, &totalDuration)) {
                slider->setRange(0, totalDuration/GST_SECOND);
            }
        }
        if (gst_element_query_position (pipeline, GST_FORMAT_TIME, &current)) {
            g_print("%ld / %ld\n", current/GST_SECOND, totalDuration/GST_SECOND);
            slider->setValue(current/GST_SECOND);
        }
    }
}

void PlayerWindow::onSeek() {
    gint64 pos = slider->sliderPosition();
    g_print("seek: %ld\n", pos);
    gst_element_seek_simple (pipeline, GST_FORMAT_TIME, GST_SEEK_FLAG_FLUSH ,
                  pos * GST_SECOND);
}

void PlayerWindow::onEos() {
    gst_element_set_state (pipeline, GST_STATE_NULL);
}

gboolean PlayerWindow::postGstMessage(GstBus * bus, GstMessage * message, gpointer user_data) {
    PlayerWindow *pw = NULL;
    if (user_data) {
        pw = reinterpret_cast<PlayerWindow*>(user_data);
    }
    switch (GST_MESSAGE_TYPE(message)) {
        case GST_MESSAGE_STATE_CHANGED: {
            GstState old_state, new_state, pending_state;
            gst_message_parse_state_changed (message, &old_state, &new_state, &pending_state);
            pw->sigState(new_state);
            break;
        }
        case GST_MESSAGE_TAG: {
            GstTagList *tags = NULL;
            gst_message_parse_tag(message, &tags);
            gchar *album= NULL;
            if (gst_tag_list_get_string(tags, GST_TAG_ALBUM, &album)) {
                pw->sigAlbum(album);
                g_free(album);
            }
            gst_tag_list_unref(tags);
            break;
        }
        case GST_MESSAGE_EOS: {
            pw->sigEos();
            break;
        }
        default:
            break;
    }
    return TRUE;
}

int main(int argc, char *argv[])
{
  gst_init (&argc, &argv);
  QApplication app(argc, argv);
  app.connect(&app, SIGNAL(lastWindowClosed()), &app, SLOT(quit ()));

  // prepare the pipeline
  GstElement *pipeline = gst_parse_launch ("playbin uri=file:///home/john/video/sintel_trailer-480p.webm", NULL);

  // prepare the ui
  PlayerWindow *window = new PlayerWindow(pipeline);
  window->resize(900, 600);
  window->show();

  // seg window id to gstreamer
  GstElement *vsink = gst_element_factory_make ("ximagesink", "vsink");
  WId xwinid = window->getVideoWId();
  gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (vsink), xwinid);
  g_object_set(GST_OBJECT(pipeline), "video-sink", vsink, NULL);

  // connect to interesting signals
  GstBus *bus = gst_element_get_bus(pipeline);
  gst_bus_add_watch(bus, &PlayerWindow::postGstMessage, window);
  gst_object_unref(bus);

  // run the pipeline
  GstStateChangeReturn sret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
  if (sret == GST_STATE_CHANGE_FAILURE) {
    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);
    // Exit application
    QTimer::singleShot(0, QApplication::activeWindow(), SLOT(quit()));
  }

  int ret = app.exec();

  window->hide();
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);

  return ret;
}

qtoverlay.pro

QT += core gui widgets
TARGET = qtoverlay

INCLUDEPATH += /usr/include/glib-2.0
INCLUDEPATH += /usr/lib/x86_64-linux-gnu/glib-2.0/include
INCLUDEPATH += /usr/include/gstreamer-1.0
INCLUDEPATH += /usr/lib/x86_64-linux-gnu/gstreamer-1.0/include
LIBS += -lgstreamer-1.0 -lgobject-2.0 -lglib-2.0 -lgstvideo-1.0

SOURCES += qtoverlay.cpp
HEADERS += qtoverlay.h

分別保存以上內容到各個文件，執行下列命令便可獲得可執行程序。若是找不到頭文件及庫文件，須要根據實際路徑修改qtoverlay.pro文件中的內容。

qmake -o Makefile qtoverlay.pro
make

 

源碼分析

  // prepare the pipeline
  GstElement *pipeline = gst_parse_launch ("playbin uri=file:///home/jleng/video/sintel_trailer-480p.webm", NULL);

  // prepare the ui
  PlayerWindow *window = new PlayerWindow(pipeline);
  window->resize(900, 600);
  window->show();

　　在main函數中對GStreamer進行初始化及建立了QT的應用對象後，構造了Pipline，構造GUI窗口對象。在PlayerWindow的構造函數中初始化按鈕及窗口，同時建立定時刷新進度條的Timer。

 

  // seg window id to gstreamer
  GstElement *vsink = gst_element_factory_make ("ximagesink", "vsink");
  WId xwinid = window->getVideoWId();
  gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (vsink), xwinid);
  g_object_set(GST_OBJECT(pipeline), "video-sink", vsink, NULL);
  ...
  gst_bus_add_watch(bus, &PlayerWindow::postGstMessage, window);
  ...
  GstStateChangeReturn sret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
  ...
  int ret = app.exec();
  ...

　　接着咱們單首創建了ximagesink用於視頻渲染，同時咱們將Qt建立的視頻窗口ID設置給GStreamer，讓GStreamer獲得渲染的窗口ID，接着使用g_object_set()將自定義的Sink經過「video-sink」屬性設置到playbin中。
　　同時，咱們設置了GStreamer的消息處理函數，全部的消息都會在postGstMessage函數中被轉發。爲了後續調用GUI對象中的接口，咱們須要將GUI窗口指針做爲user-data，在postGstMessage中再轉換爲GUI對象。
　　接着設置Pipeline的狀態爲PLAYING開始播放。
　　最後調用GUI框架的事件循環，exec()會一直執行，直到關閉窗口。
　　因爲GStreamer的GstBus會默認使用GLib的主循環及事件處理機制，因此必需要保證GLi默認的MainLoop在某個線程中運行。在本例中，Qt在Linux下會自動使用GLib的主循環，因此咱們無需額外進行處理。

 

gboolean PlayerWindow::postGstMessage(GstBus * bus, GstMessage * message, gpointer user_data) {
    PlayerWindow *pw = NULL;
    if (user_data) {
        pw = reinterpret_cast<PlayerWindow*>(user_data);
    }
    switch (GST_MESSAGE_TYPE(message)) {
        case GST_MESSAGE_STATE_CHANGED: {
            GstState old_state, new_state, pending_state;
            gst_message_parse_state_changed (message, &old_state, &new_state, &pending_state);
            pw->sigState(new_state);
            break;
        }
        case GST_MESSAGE_TAG: {
            GstTagList *tags = NULL;
            gst_message_parse_tag(message, &tags);
            gchar *album= NULL;
            if (gst_tag_list_get_string(tags, GST_TAG_ALBUM, &album)) {
                pw->sigAlbum(album);
                g_free(album);
            }
            gst_tag_list_unref(tags);
            break;
        }
        case GST_MESSAGE_EOS: {
            pw->sigEos();
            break;
        }
        default:
            break;
    }
    return TRUE;
}

　　咱們在轉換後GUI對象後，再根據消息類型進行處理。在postGstMessage中咱們沒有直接更新GUI，由於GStreamer的Bus處理線程與GUI主線程可能爲不一樣線程，直接更新GUI會出錯或無效。所以利用Qt的signal-slot機制在相應的槽函數中就行GUI信息的更新。這裏只處理了3種消息STATE_CHANGED（狀態變化），TAG（媒體元數據及編碼信息），EOS（播放結束），GStreamer所支持的消息可查看官方文檔GstMessage。

 

void PlayerWindow::onPlayClicked() {
    GstState st = GST_STATE_NULL;
    gst_element_get_state (pipeline, &st, NULL, GST_CLOCK_TIME_NONE);
    if (st < GST_STATE_PAUSED) {
        // Pipeline stopped, we need set overlay again
        GstElement *vsink = gst_element_factory_make ("ximagesink", "vsink");
        g_object_set(GST_OBJECT(pipeline), "video-sink", vsink, NULL);
        WId xwinid = getVideoWId();
        gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (vsink), xwinid);
    }
    gst_element_set_state (pipeline, GST_STATE_PLAYING);
}

　　當點擊Play按鈕時，onPlayClicked函數會被調用，咱們在此直接調用GStreamer的接口設置Pipeline的狀態。當播放結束或點擊Stop時，GStreamer會在狀態切換到NULL時釋放全部資源，因此咱們在此須要從新設置playbin的vido-sink，並指定視頻輸出窗口。

　　Pause，Stop的處理相似，直接調用gst_element_set_state ()將Pipeline設置爲相應狀態。

 

void PlayerWindow::refreshSlider() {
    gint64 current = GST_CLOCK_TIME_NONE;
    if (state == GST_STATE_PLAYING) {
        if (!GST_CLOCK_TIME_IS_VALID(totalDuration)) {
            if (gst_element_query_duration (pipeline, GST_FORMAT_TIME, &totalDuration)) {
                slider->setRange(0, totalDuration/GST_SECOND);
            }
        }
        if (gst_element_query_position (pipeline, GST_FORMAT_TIME, &current)) {
            g_print("%ld / %ld\n", current/GST_SECOND, totalDuration/GST_SECOND);
            slider->setValue(current/GST_SECOND);
        }
    }
}

void PlayerWindow::onSeek() {
    gint64 pos = slider->sliderPosition();
    g_print("seek: %ld\n", pos);
    gst_element_seek_simple (pipeline, GST_FORMAT_TIME, GST_SEEK_FLAG_FLUSH ,
                  pos * GST_SECOND);
}

　　咱們在構造函數中建立了Timer用於每秒刷新進度條，在refreshSlider被調用時，咱們經過gst_element_query_duration() 和gst_element_query_position ()獲得文件的總時間和當前時間，並刷新進度條。因爲GStreamer返回時間單位爲納秒，因此咱們須要經過GST_SECOND將其轉換爲秒用於時間顯示。
　　咱們一樣處理了用戶的Seek操做，在拉動進度條到某個位置時，獲取Seek的位置，調用gst_element_seek_simple ()跳轉到指定位置。咱們不用關心對GStreamer的調用是處於哪一個線程，GStreamer內部會自動進行處理。

 

總結

經過本文，咱們學習到：

• 如何使用gst_video_overlay_set_window_handle ()將GUI的窗口句柄傳遞給GStremaer。
• 如何使用信號槽傳遞消息到GUI主線程。
• 如何使用Timer定時刷新GUI。

 

引用

https://gstreamer.freedesktop.org/documentation/video/gstvideooverlay.html?gi-language=c
https://gstreamer.freedesktop.org/documentation/tutorials/basic/toolkit-integration.html?gi-language=c
https://doc.qt.io/qt-5/qmake-manual.html

 

做者： John.Leng

出處： http://www.cnblogs.com/xleng/

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