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

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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_22">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/includeLIBS += 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);
}