Gstreamer教程 -時間
阿新 • • 發佈：2018-11-07
#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 */ //僅包含playbin2一個element就足夠實現播放，參見教程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 { //設定100毫秒超時，每10s呼叫一次，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查詢當前播放時間 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查詢總時間 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; //建立新seeking物件，gst_element_query將物件傳至管道 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); }
跳轉功能
gst_element_seek_simple(）
讓我們看一下這個方法的各個引數：
GST_FORMAT_TIME說明我們的操作（跳轉）是針對時間來計算的（有兩種計算方式，時間和資料）。
然後是GstSeekFlags，這裡主要介紹常見的幾個：
GST_SEEK_FLAG_FLUSH：跳轉後會丟棄當前pipeline裡面所有的資料，因為要重新解析一段資料，所以會有一個停頓，但在使用者看來可以保證應用的快速響應；反之，就會繼續播放一點內容，然後再跳轉。
GST_SEEK_FLAG_KEY_UNIT:大部分編碼的視訊流是無法精確定位到某個特定時刻的，只能是到某些幀（稱為key frame）。當這個標誌被置時，會自動定位到最近的一個key frame然後開始播放。如果這個標誌不置，那麼pipeline會跳到最接近的一個key frame，然後開始播放，但此時不輸出任何東西，直到到達設定的位置。綜合來看，不設定這個標誌會更加準確，但是響應時間會顯得較長。
GST_SEEK_FLAG_ACCURATE:有些時候我們沒法獲得足夠的索引資訊，這個時候跳轉到某個位置會非常耗時。在這種情況下，GStreamer
最後，我們會跳轉到某個地方，因為我們用的是GST_FORMAT_TIME，時間的單位是用納秒來計算的，所以需要用GST_SECOND巨集來轉換一下。
來自 <http://blog.csdn.net/sakulafly/article/details/20992879>