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运行效果（音频）

 

简介

     上一个教程演示了GStreamer 概念。本教程中的管在它设置为 playing 状态之前完全构建。这没关系。如果 我们没有采取进一步的行动，数据会到达 pipeline 的 pipeline 和 pipeline 将生成错误消息并停止。但 我们将采取进一步的行动…，它允许“动态”构建管道，如 信息变得可用，而不是拥有整体式管道 在应用程序开始时定义。您将掌握开始播放教程所需的知识。审查的要点 这将是：

          • 如何在链接元素时实现更精细的控制。

          • 如何收到有趣事件的通知，以便您及时做出反应。

          • 元素可以处于的各种状态。

 

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 <QCoreApplication>
#include <QDebug>#include "gst.h"/* 结构包含我们所有的信息，这样我们就可以将其传递给回调函数 */
typedef struct _CustomData
{GstElement *pipeline;GstElement *source;GstElement *convert;GstElement *resample;GstElement *sink;
} CustomData;/* 附加信号处理器 */
static void pad_added_handler (GstElement *src, GstPad *pad, CustomData *data);int main(int argc, char *argv[])
{/* 初始化GStreamer */gst_init (&argc, &argv);/* 创建元素 */CustomData data;data.source = gst_element_factory_make ("uridecodebin", "source");data.convert = gst_element_factory_make ("audioconvert", "convert");data.resample = gst_element_factory_make ("audioresample", "resample");data.sink = gst_element_factory_make ("autoaudiosink", "sink");/* 创建空管道 */data.pipeline = gst_pipeline_new ("test-pipeline");if (!data.pipeline || !data.source || !data.convert || !data.resample || !data.sink) { g_printerr ("Not all elements could be created.\n"); return -1; }/* 建造管道 */gst_bin_add_many (GST_BIN (data.pipeline), data.source, data.convert, data.resample, data.sink, NULL);if (!gst_element_link_many (data.convert, data.resample, data.sink, NULL)){g_printerr ("Elements could not be linked.\n");gst_object_unref (data.pipeline); return -1;}/* 设置播放的URI(需带有音频) *///g_object_set (data.source, "uri", "https://gstreamer.freedesktop.org/data/media/sintel_trailer-480p.webm", NULL);g_object_set (data.source, "uri", "rtsp://192.168.1.200", NULL);/* 连接到pad-add信号 */g_signal_connect (data.source, "pad-added", G_CALLBACK (pad_added_handler), &data);/* 开始播放 */GstStateChangeReturn ret = gst_element_set_state (data.pipeline, 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.pipeline); return -1;}GstMessage *msg;gboolean terminate = FALSE;/* 从bus监听消息 */GstBus *bus = gst_element_get_bus (data.pipeline);do {// 从bus总线中获取下一个满足特定条件的消息msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE, (GstMessageType)(GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS));/* 解析消息 */if (msg != NULL){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);terminate = TRUE;break;case GST_MESSAGE_EOS:g_print ("End-Of-Stream reached.\n");terminate = TRUE;break;case GST_MESSAGE_STATE_CHANGED:/* 我们只对管道中的状态更改消息感兴趣 */if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)){GstState old_state, new_state, pending_state;gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);g_print ("Pipeline state changed from %s to %s:\n", gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));}break;default:/* 我们不应该来这里 */g_printerr ("Unexpected message received.\n");break;}gst_message_unref (msg);}} while (!terminate);/* Free resources */gst_object_unref (bus);gst_element_set_state (data.pipeline, GST_STATE_NULL);gst_object_unref (data.pipeline);return 0;
}/* 此函数将由添加了hanle的信号调用 */
/*当source element最后获得足够的数据时，它就会自动生成source pad，并且触令“pad-added”信号。这样回调就会被调用了;static void pad_added handler (GstElement *src, GstPad *new_pad, CustomData *data)说明: src是触发这个信号的GstElement。在这个例子中就是uridecodebin，也是我们唯一注册的信号。new_pad是加到src上的pad。通常来说，是我们需要连接的pad。data指针是跟随信号一起过来的参数,在这个例子中传递的是CustomData指针。
*/
static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data)
{GstPad *sink_pad = gst_element_get_static_pad (data->convert, "sink");g_print ("Received new pad '%s' from '%s':", GST_PAD_NAME (new_pad), GST_ELEMENT_NAME (src));/* 如果我们的转换器已经链接，我们在这里什么也不用做 */if (gst_pad_is_linked (sink_pad)) { g_print ("We are already linked. Ignoring.\n"); goto exit; }/* 检查新pad的类型 */GstCaps *new_pad_caps = gst_pad_get_current_caps (new_pad);GstStructure *new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);const gchar *new_pad_type = gst_structure_get_name (new_pad_struct);if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {  g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type); goto exit;  }/* 尝试链接 */GstPadLinkReturn ret = gst_pad_link (new_pad, sink_pad);if (GST_PAD_LINK_FAILED (ret)){g_print ("Type is '%s' but link failed.\n", new_pad_type);}else{g_print ("Link succeeded (type '%s').\n", new_pad_type);}exit:/* 如果我们有新pad的caps，请不要参考 */if (new_pad_caps != NULL){gst_caps_unref (new_pad_caps);}/* 减小引用计数sink_pad */gst_object_unref (sink_pad);
}

 

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笔者 - jxd