#include<gst/gst.h>
/* Structure to contain all our information, so we can passit around */
typedefstruct _CustomData {
GstElement *playbin2; /* Our one and only element */
gboolean playing; /* Are we in the PLAYING state? */
gboolean terminate; /* Should we terminate execution? */
gboolean seek_enabled; /* Is seeking enabledfor this media? */
gboolean seek_done; /* Have we performed the seek already? */
gint64 duration; /* How long does this media last, innanoseconds */
}CustomData;
/* Forward definition of the message processing function */
staticvoid handle_message (CustomData *data, GstMessage *msg);
intmain(int argc, char *argv[]) {
CustomData data;
GstBus *bus;
GstMessage *msg;
GstStateChangeReturn ret;
data.playing = FALSE;
data.terminate = FALSE;
data.seek_enabled = FALSE;
data.seek_done = FALSE;
data.duration = GST_CLOCK_TIME_NONE;
/*Initialize GStreamer */
gst_init (&argc, &argv);
/* Create the elements */
//仅包含playbin2一个element就足够实现播放，参见教程01
data.playbin2 = gst_element_factory_make("playbin2", "playbin2");
if (!data.playbin2) {
g_printerr ("Not all elements could becreated.\n");
return -1;
}
/* Set the URI to play */
g_object_set (data.playbin2, "uri","http://docs.gstreamer.com/media/sintel_trailer-480p.webm",NULL);
/* Start playing */
ret = gst_element_set_state (data.playbin2,GST_STATE_PLAYING);
if (ret == GST_STATE_CHANGE_FAILURE) {
g_printerr ("Unable to set thepipeline to the playing state.\n");
gst_object_unref (data.playbin2);
return -1;
}
/* Listen to the bus*/
bus = gst_element_get_bus (data.playbin2);
do {
//设置100毫秒超时，每10s调用一次，返回NULL
msg = gst_bus_timed_pop_filtered(bus, 100 * GST_MSECOND,
GST_MESSAGE_STATE_CHANGED |GST_MESSAGE_ERROR | GST_MESSAGE_EOS | GST_MESSAGE_DURATION);
/* Parse message */
if (msg != NULL) {
handle_message (&data, msg);
} else {
/* We got no message,this means the timeout expired */
if (data.playing) {
GstFormat fmt = GST_FORMAT_TIME;
gint64 current = -1;
/* Query the currentposition of the stream */
//gst_element_query_position查询当前播放时间
if (!gst_element_query_position(data.playbin2, &fmt, ¤t)) {
g_printerr ("Could not querycurrent position.\n");
}
/* If we didn't knowit yet, query the stream duration */
//gst_element_query_duration查询总时间
if (!GST_CLOCK_TIME_IS_VALID(data.duration)) {
if (!gst_element_query_duration(data.playbin2, &fmt, &data.duration)) {
g_printerr ("Could not querycurrent duration.\n");
}
}
/* Print current position and total duration */
g_print ("Position %" GST_TIME_FORMAT" / %" GST_TIME_FORMAT "\r",
GST_TIME_ARGS (current),GST_TIME_ARGS (data.duration));
/* If seeking isenabled, we have not done it yet, and the time is right, seek */
if (data.seek_enabled &&!data.seek_done && current > 10 * GST_SECOND) {
g_print ("\nReached 10s,performing seek...\n");
gst_element_seek_simple(data.playbin2, GST_FORMAT_TIME,
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.playbin2,GST_STATE_NULL);
gst_object_unref (data.playbin2);
return 0;
}
staticvoid 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 fromelement %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 ("End-Of-Streamreached.\n");
data->terminate = TRUE;
break;
case GST_MESSAGE_DURATION:
/* The duration has changed, mark thecurrent one as invalid */
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->playbin2)) {
g_print ("Pipeline state changedfrom %s to %s:\n",
gst_element_state_get_name(old_state), gst_element_state_get_name (new_state));
/* Remember whether weare in the PLAYING state or not */
data->playing = (new_state ==GST_STATE_PLAYING);
if (data->playing) {
/* We just moved to PLAYING. Check ifseeking is possible */
GstQuery *query;
gint64 start, end;
//创建新seeking对象，gst_element_query将对象传至管道
query = gst_query_new_seeking (GST_FORMAT_TIME);
if (gst_element_query(data->playbin2, query)) {
gst_query_parse_seeking(query, NULL, &data->seek_enabled, &start, &end);
if (data->seek_enabled) {
g_print ("Seeking is ENABLEDfrom %" GST_TIME_FORMAT " to %" GST_TIME_FORMAT "\n",
GST_TIME_ARGS (start),GST_TIME_ARGS (end));
} else {
g_print ("Seeking isDISABLED for this stream.\n");
}
}
else {
g_printerr ("Seeking queryfailed.");
}
gst_query_unref (query);
}
}
} break;
default:
/* We should not reach here */
g_printerr ("Unexpected messagereceived.\n");
break;
}
gst_message_unref (msg);
}
跳转功能
gst_element_seek_simple(）
让我们看一下这个方法的各个参数：
GST_FORMAT_TIME说明我们的操作（跳转）是针对时间来计算的（有两种计算方式，时间和数据）。
然后是GstSeekFlags，这里主要介绍常见的几个：
GST_SEEK_FLAG_FLUSH：跳转后会丢弃当前pipeline里面所有的数据，因为要重新解析一段数据，所以会有一个停顿，但在用户看来可以保证应用的快速响应；反之，就会继续播放一点内容，然后再跳转。
GST_SEEK_FLAG_KEY_UNIT:大部分编码的视频流是无法精确定位到某个特定时刻的，只能是到某些帧（称为key frame）。当这个标志被置时，会自动定位到最近的一个key frame然后开始播放。如果这个标志不置，那么pipeline会跳到最接近的一个key frame，然后开始播放，但此时不输出任何东西，直到到达设定的位置。综合来看，不设置这个标志会更加准确，但是响应时间会显得较长。
GST_SEEK_FLAG_ACCURATE:有些时候我们没法获得足够的索引信息，这个时候跳转到某个位置会非常耗时。在这种情况下，GStreamer通常就是估计一下大概的位置（一般都很准确）。如果你实际运行发现这个不够准确，那么可以置这个标志位。必须了解的是，这个标志位一旦设置，跳转的时间会大大增加。
最后，我们会跳转到某个地方，因为我们用的是GST_FORMAT_TIME，时间的单位是用纳秒来计算的，所以需要用GST_SECOND宏来转换一下。
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来自 <http://blog.csdn.net/sakulafly/article/details/20992879>