GStreamer —— 2.4、Windows下Qt加载GStreamer库后运行 - “教程4:时间管理及seek操作“（附：完整源码）

运行效果

简介

     上一个教程演示了动态管道概念。本教程中介绍GstQuery。GstQuery是一种机制，允许向元素或pad请求信息。在此示例中，我们询问管道 seek是否为允许（某些来源（如直播）不允许查找）。如果它允许，那么一旦影片播放了10 秒，我们使用Seek跳到其他位置。在前面的教程中，设置并运行管道后， 我们的main函数只是坐着等待通过 bus接收消息。这里，我们修改这个函数来周期性地唤醒并查询pipeline以获取stream位置，以便我们可以实时轮询操作。这类似于媒体播放器执行的作，更新用户界面。最后，每当流持续时间发生变化时，都会查询并更新流持续时间。

          • 如何查询管道以获取流位置和总时间。

          • 如何在流中进行seek操作

GStreamer相关运行库

INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0/gst
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/glib-2.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0/include

LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gstreamer-1.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gobject-2.0.lib

完整源码

#include <gst/gst.h>

typedef struct _CustomData
{
    GstElement *playbin;    /* 唯一的元素 */
    gboolean playing;       /* 是否处于播放状态？ */
    gboolean terminate;     /* 是否终止？ */
    gboolean seek_enabled;  /* 是否启用了seek功能？ */
    gboolean seek_done;     /* 是否已进行seek？ */
    gint64 duration;        /* 此媒体总时长 */
} CustomData;

/* 消息处理功能的转发定义 */
static void handle_message (CustomData *data, GstMessage *msg);

int main(int argc, char *argv[])
{
    CustomData data;
    data.playing = FALSE;
    data.terminate = FALSE;
    data.seek_enabled = FALSE;
    data.seek_done = FALSE;
    data.duration = GST_CLOCK_TIME_NONE;

    /* 初始化GStreamer */
    gst_init (&argc, &argv);

    /* 创建元素 */
    data.playbin = gst_element_factory_make ("playbin", "playbin");
    if (!data.playbin) { g_printerr ("Not all elements could be created.\n");  return -1; }

    /* 设置要播放的URI */
    g_object_set (data.playbin, "uri", "https://gstreamer.freedesktop.org/data/media/sintel_trailer-480p.webm", NULL);

    /* 开始播放 */
    GstStateChangeReturn ret = gst_element_set_state (data.playbin, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE)
    {
        g_printerr ("Unable to set the pipeline to the playing state.\n");
        gst_object_unref (data.playbin); return -1;
    }

    GstMessage *msg;
    /* 监听bus消息 */
    GstBus *bus = gst_element_get_bus (data.playbin);
    do
    {
        /* 等待接收bus的符合条件的消息 */
        msg = gst_bus_timed_pop_filtered (bus, 100 * GST_MSECOND, (GstMessageType)(GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS | GST_MESSAGE_DURATION));

        /* 解析消息 */
        if (msg != NULL) { handle_message (&data, msg); }
        else
        {
            /* 我们没有收到消息，这意味着超时已过 */
            if (data.playing)
            {
                gint64 current = -1;

                /* 查询流的当前位置 */
                if (!gst_element_query_position (data.playbin, GST_FORMAT_TIME, &current))
                {
                    g_printerr ("Could not query current position.\n");
                }

                /* 查询流持续时间 */
                if (!GST_CLOCK_TIME_IS_VALID (data.duration))
                {
                    if (!gst_element_query_duration (data.playbin, GST_FORMAT_TIME, &data.duration))
                    {
                        g_printerr ("Could not query current duration.\n");
                    }
                }

                /* 打印当前位置和总持续时间 */
                g_print ("Position %" GST_TIME_FORMAT " / %" GST_TIME_FORMAT "\r",GST_TIME_ARGS (current), GST_TIME_ARGS (data.duration));

                /* 如果能够seek，我们还没有做那现在正是时候seek */
                if (data.seek_enabled && !data.seek_done && current > 10 * GST_SECOND)
                {
                    g_print ("\nReached 10s, performing seek...\n");
                    gst_element_seek_simple (data.playbin, GST_FORMAT_TIME, (GstSeekFlags)(GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_KEY_UNIT), 30 * GST_SECOND);
                    data.seek_done = TRUE;
                }
            }
        }
    } while (!data.terminate);

    /* Free resources */
    gst_object_unref (bus);
    gst_element_set_state (data.playbin, GST_STATE_NULL);
    gst_object_unref (data.playbin);
    return 0;
}

static void handle_message (CustomData *data, GstMessage *msg)
{
    GError *err;
    gchar *debug_info;
    switch (GST_MESSAGE_TYPE (msg))
    {
    case GST_MESSAGE_ERROR:
        gst_message_parse_error (msg, &err, &debug_info);
        g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
        g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
        g_clear_error (&err); g_free (debug_info); data->terminate = TRUE; break;
    case GST_MESSAGE_EOS:
        g_print ("\nEnd-Of-Stream reached.\n");
        data->terminate = TRUE; break;
    case GST_MESSAGE_DURATION:
        /* 持续时间已更改，请将当前持续时间标记为无效 */
        data->duration = GST_CLOCK_TIME_NONE; break;
    case GST_MESSAGE_STATE_CHANGED:
    {
        GstState old_state, new_state, pending_state;
        gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);
        if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data->playbin))
        {
            g_print ("Pipeline state changed from %s to %s:\n",gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));

            /* 记住我们是否处于播放状态 */
            data->playing = (new_state == GST_STATE_PLAYING);

            /* 若此时是播放状态 */
            if (data->playing)
            {
                /* 刚刚seek了，检查是否在seek中 */
                GstQuery *query = gst_query_new_seeking (GST_FORMAT_TIME);
                if (gst_element_query (data->playbin, query))
                {
                    gint64 start, end;
                    gst_query_parse_seeking (query, NULL, &data->seek_enabled, &start, &end);
                    if (data->seek_enabled)
                    {
                        g_print ("Seeking is ENABLED from %" GST_TIME_FORMAT " to %" GST_TIME_FORMAT "\n", GST_TIME_ARGS (start), GST_TIME_ARGS (end));
                    }
                    else
                    {
                        g_print ("Seeking is DISABLED for this stream.\n");
                    }
                }
                else
                {
                    g_printerr ("Seeking query failed.");
                }
                gst_query_unref (query);
            }
        }
    } break;
    default:
        /* We should not reach here */
        g_printerr ("Unexpected message received.\n");
        break;
    }
    gst_message_unref (msg);
}

关注

笔者 - jxd