在虛擬攝像頭程序的設(shè)計(jì)中，我們將用gstreamer作為數(shù)據(jù)源，為directshow注冊攝像頭程序提供數(shù)據(jù)源。
創(chuàng)建數(shù)據(jù)源類型
我們創(chuàng)建一個(gè)數(shù)據(jù)源vcamsource, 這個(gè)vcamsource將包含gststream的實(shí)例， 在VcamSource的私有屬性_VcamSourcePriv 中我們聲明了四個(gè)gstElement元素雏赦，分別代表pipeline，pipeline，capsfilter 星岗，sink：
/**** 注釋掉這部分填大，因?yàn)镚_DECLARE_DERIVABLE_TYPE 中已經(jīng)定義了這個(gè)類
struct _VcamSource {
GObject parent_instance;
};
***/
struct _VcamSourcePrivate {
gboolean status;
GstElement* pipeline, * source, *capsfilter ， * sink;
};
pipeline時(shí)streamer的容器伍茄，source時(shí)streamer的產(chǎn)生源栋盹，capsfilter是媒體格式過濾去，sink是stream的最終渲染器敷矫。我們將使用videotestsrc插件作為source例获，他會隨機(jī)生成stream, 同時(shí)使用appsink插件作為sink，它可以提供外部程序訪問stream中的數(shù)據(jù)曹仗。
需要注意的是在.h頭文件中榨汤，G_DECLARE_DERIVABLE_TYPE已經(jīng)包含了對_VcamSource 的定義，所以不要重復(fù)定義怎茫，另外_VcamSourcePrivate是一個(gè)私有屬性收壕，我們將用下面的宏將它加入，并且它的名字不可以改變必須是ModuleObjName##Private：
G_DEFINE_TYPE_WITH_CODE(VcamSource, vcam_source, G_TYPE_OBJECT, G_ADD_PRIVATE(VcamSource) )
#define VCAM_SOURCE_GET_PRIVATE(obj) ( G_TYPE_INSTANCE_GET_PRIVATE((obj), VCAM_TYPE_SOURCE, VcamSourcePrivate))
新的私有函數(shù)的定義轨蛤，需要使用G_ADD_PRIVATE宏蜜宪，他被作為額外的執(zhí)行代碼放在G_DEFINE_TYPE_WITH_CODE中，所以這里要注意祥山，使用G_DEFINE_TYPE_WITH_CODE替換G_DEFINE_TYPE圃验； 并在在class_init文件中不在需要, VCAM_SOURCE_GET_PRIVATE宏仍然保留，用于獲取私有的屬性缝呕，仍舊需要注意第三個(gè)參數(shù)澳窑，VcamSourcePrivate，他的格式是ModuleObjName##Private供常，不要更改摊聋。
vcam_source_class_init(VcamSourceClass *kclass) {
//使用G_ADD_PRIVATE配合G_DEFINE_TYPE_WITH_CODE宏，不在需要g_type_class_add_private自己添加私有屬性栈暇， commnet out it
//g_type_class_add_private(kclass, sizeof(VcamSourcePriv));
gstreamer在VcamSource的工作步驟
在VcamSource實(shí)現(xiàn)gstreamer流程需要以下的步驟：
- Gstreamer在執(zhí)行前需要初始化（gst_init (&argc, &argv);）麻裁，但這個(gè)初始化操作最好在系統(tǒng)入口處，所以在vcamsource中我們不進(jìn)行g(shù)streamer的初始化源祈，而是在初次引入VcamSource的時(shí)候煎源，先對gist系統(tǒng)做初始化。
- 分別創(chuàng)建source, pipleline, sink等元素
我們將為每一個(gè)VcamSource實(shí)例分別創(chuàng)建一個(gè)gstreamer實(shí)例新博，有多個(gè)VcamSource時(shí)薪夕，就會對應(yīng)多個(gè)實(shí)例脚草。所以這些元素的創(chuàng)建赫悄，被我們放在object_init方法里：
static void
vcam_source_init(VcamSource *d) {
......
/* Create the elements */
VcamSourcePriv* priv = VCAM_SOURCE_GET_PRIVATE(d);
priv ->source= gst_element_factory_make("videotestsrc", "source");
priv ->capsfilter = gst_element_factory_make("capsfilter ", "caps");
priv->sink = gst_element_factory_make ("appsink", "app_sink");
/* Create the empty pipeline */
priv->pipeline = gst_pipeline_new("test-pipeline");
}
source在gstreamer中代表的是數(shù)據(jù)源元素，我們使用videotestsrc來作為初始驗(yàn)證源（測試方案用），他將產(chǎn)生測試用vedio數(shù)據(jù)埂淮。 同時(shí)姑隅，我們將采用GstAppSink作為gststream視頻的render(實(shí)際只輸出數(shù)據(jù)，并不渲染窗口)倔撞。
appSink的不同之處在于它提供了額外的API讲仰，可以允許外部程序提取stream內(nèi)的數(shù)據(jù)（sample). appSink使用queue來儲存來自streamer線程的數(shù)據(jù)，可以設(shè)置drop屬性痪蝇，當(dāng)queue滿了的時(shí)候鄙陡，就及時(shí)得drop掉數(shù)據(jù)；相對于自己寫一個(gè)滿足需要的sink插件躏啰，appsink還是很方便的趁矾。
capsfilter 作為過濾器，并不能修改數(shù)據(jù)给僵，但是能夠限制數(shù)據(jù)的格式毫捣，在這里可以限制videotestsrc 產(chǎn)生的數(shù)據(jù)格式。
- 組裝pipleLine
在使用pipleLine前我們需要將所有的gstreamer 元素組裝起來：
static void
vcam_source_init(VcamSource *d) {
......
/* Create the elements */
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(d);
priv ->source= gst_element_factory_make("videotestsrc", "source");
priv->sink = gst_element_factory_make("appsink", "app_sink");
priv->capsfilter = gst_element_factory_make("capsfilter ", "caps");
/* Create the empty pipeline */
priv->pipeline = gst_pipeline_new("test-pipeline");
if (!priv->pipeline || !priv->source || !priv->sink) {
g_printerr("Not all elements could be created.\n");
return -1;
}
/* Build the pipeline */
gst_bin_add_many(GST_BIN(priv->pipeline), priv->source, priv->capsfilter, priv->sink, NULL);
//if (gst_element_link(priv->source, priv->sink) != TRUE) {
if (gst_element_link(priv->source, priv->capsfilter) != TRUE || gst_element_link(priv->capsfilter, priv->sink) != TRUE) {
g_printerr("Elements could not be linked.\n");
gst_object_unref(priv->pipeline);
return -1;
}
}
gstreamer 元素的組裝也是在 vcam_source對象初始化的函數(shù)中來完成帝际， 連接的路線是 videotestsrc | capsfilter | appsink.
- 配置filter和appsink
capsfilter主要用來限制testsrc的輸出格式蔓同，我們需要在pipleline調(diào)用前，先給提供一個(gè)默認(rèn)的格式：
video/x-raw, width=640, height=480, format=RGB //表示640X480 RGB frame
filter 和appsink的設(shè)置也是在初始化函數(shù)中完成：
static void
vcam_source_init(VcamSource *d) {
....
/* Create the elements */
....
/**設(shè)置 fitler caps**/
GstCaps* caps = gst_caps_new_simple("video/x-raw",
"format", G_TYPE_STRING, "RGB",
"framerate", GST_TYPE_FRACTION, 25, 1,
"width", G_TYPE_INT, 640,
"height", G_TYPE_INT, 480,
NULL);
g_object_set(priv->capsfilter, "caps", caps, NULL);
/**設(shè)置appsink的max-buffers來限制buffer大小蹲诀，
設(shè)置drop屬性斑粱，允許queue滿意后自動blockthread或drop舊的buffer**/
gst_app_sink_set_max_buffers(priv->sink, 500); // limit number of buffers queued
gst_app_sink_set_drop(priv->sink, TRUE); // drop old buffers in queue when full
/* Build the pipeline */
....
}
- 啟動pipleLine
pipleline的啟動就是獎(jiǎng)狀臺設(shè)置為GST_STATE_PLAYING， 但是并不是創(chuàng)建完就啟動的侧甫，相反VcamSource中我們需要提供一個(gè)啟動函數(shù)珊佣，讓用戶或調(diào)用程序，顯示的啟動pipleLine.
在.h頭文件中披粟，我們聲明一個(gè)start函數(shù)咒锻，以及一個(gè)幫助函數(shù)：
struct _VcamSourceClass {
GObjectClass parent_class;
.......
gshort (*start)(VcamSource* self);
.....
};
void vcam_source_getMediaTyp(VcamSource *self, VcamIMediaType* typeptr);
gshort vcam_source_start(VcamSource* self);
在.c文件中，我們需要?jiǎng)?chuàng)建start的默認(rèn)實(shí)現(xiàn)函數(shù)守屉，以及vcam_source_start幫助函數(shù)惑艇， 并且將start指針指向默認(rèn)實(shí)現(xiàn)函數(shù)：
//start pipleline
static gshort startimpl(VcamSource* self) {
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(self);
GstStateChangeReturn ret;
/* Start playing */
ret = gst_element_set_state(priv->pipeline, GST_STATE_PLAYING);
if (ret == GST_STATE_CHANGE_FAILURE) {
g_printerr("Unable to set the pipeline to the playing state (check the bus for error messages).\n");
return -1; //啟動失敗
}
else {
priv->status = TRUE;
return 0;
}
}
gshort vcam_source_start(VcamSource* self) {
VcamSourceClass *klass = VCAM_SOURCE_GET_CLASS(self);
if (klass->start == NULL) return -2; //函數(shù)未初始化
return klass->start(self);
}
static void
vcam_source_class_init(VcamSourceClass *kclass) {
//不在需要手動注冊私有屬性
// g_type_class_add_private(kclass, sizeof(VcamSourcePriv));
.....
kclass->start = startimpl;
.......
}
在pipleline成功start以后，我們會將vcamsource的狀態(tài)設(shè)置為true.
- 獲取來自gst appsink的數(shù)據(jù)
appsink可以提供外部程序訪問stream中數(shù)據(jù)的能力拇泛。通過appsink訪問視頻samples的方法通常包括 GstApp.AppSink.prototype.pull_sample和 GstApp.AppSink.prototype.pull_preroll滨巴， 它們是同步方式，這兩個(gè)方法會一致出去block狀態(tài)俺叭， 除非新的samples已經(jīng)可以被訪問恭取，或者sink關(guān)閉里，stream流到了末尾熄守，它們才會返回蜈垮。
當(dāng)然耗跛， appsink對這兩個(gè)函數(shù)也提供了timeout的版本，GstApp.AppSink.prototype.try_pull_sample 和 GstApp.AppSink.prototype.try_pull_preroll攒发，它們連個(gè)額外接收一個(gè)timeout的參數(shù)调塌，用于限制等待的時(shí)間。
pull_sample主要用于appsink在PlAYING狀態(tài)下獲取sample, 而pull_preroll則是當(dāng)PlAYING處于PAUSED狀態(tài)時(shí)惠猿，獲取最近的預(yù)撥（preroll）sample羔砾。特別是當(dāng)發(fā)生seek后，調(diào)用該方法可以立刻獲得seek位置的數(shù)據(jù)偶妖。
vcamsource將同樣提供兩個(gè)方法姜凄，讓使用者可以方便的訪問視頻數(shù)據(jù)，同時(shí)忽略內(nèi)部的實(shí)現(xiàn)：
void vcam_source_pull_sample(VcamSource self, Gst.Sample sample)
void vcam_source_pull_preroll(VcamSource self, Gst.Sample sample)
并在.c文件中完成它們的實(shí)現(xiàn)趾访，在當(dāng)前階段檀葛，我們只是簡單的返回gstsample:
void vcam_source_pull_sample(VcamSource* self, GstSample* sample) {
VcamSourcePriv* private = VCAM_SOURCE_GET_PRIVATE(self);
g_return_if_fail(priv->sink != NULL);
sample = gst_app_sink_pull_sample(priv->sink);
if (sample == NULL && gst_app_sink_is_eos(priv->sink)) {
g_print("the stream reach the ond \n");
//send out singal for eof of stream
}
else
{
g_print("gst_app_sink_pull_sample returned null\n");
return NULL;
}
}
void vcam_source_pull_preroll(VcamSource* self, GstSample* sample) {
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(self);
g_return_if_fail(priv->sink != NULL);
sample = gst_app_sink_pull_preroll(priv->sink);
if (sample == NULL && gst_app_sink_is_eos(priv->sink)) {
g_print("the stream reach the ond \n");
//send out singal for eof of stream
}else{
g_print("gst_app_sink_pull_preroll returned null\n");
}
}
gststreamer元素的銷毀
每一個(gè)vcamsource元素，包含一個(gè)stream pipleline, 當(dāng)vcamsource由于任何原因走向銷毀得時(shí)候腹缩，我們需要同時(shí)銷毀stream得所有元素屿聋。
在VcamSource中我們增肌內(nèi)存管理所需的函數(shù)，這些函數(shù)將幫我們最終銷毀VcamSource中創(chuàng)建的所有g(shù)streamer 元素：
static void
vcam_source_dispose(GObject* gobject)
{
VcamSourcePriv* priv = VCAM_SOURCE_GET_PRIVATE(gobject);
/* In dispose(), you are supposed to free all types referenced from this
* object which might themselves hold a reference to self. Generally,
* the most simple solution is to unref all members on which you own a
* reference.
*/
/* dispose() might be called multiple times, so we must guard against
* calling g_object_unref() on an invalid GObject by setting the member
* NULL; g_clear_object() does this for us.
*/
gst_element_set_state(priv->pipeline, GST_STATE_NULL);
g_clear_object(&priv->pipeline);
/* Always chain up to the parent class; there is no need to check if
* the parent class implements the dispose() virtual function: it is
* always guaranteed to do so
*/
G_OBJECT_CLASS(vcam_source_parent_class)->dispose(gobject);
}
static void
vcam_source_finalize(GObject* gobject)
{
/* Always chain up to the parent class; as with dispose(), finalize()
* is guaranteed to exist on the parent's class virtual function table
*/
G_OBJECT_CLASS(vcam_source_parent_class)->finalize(gobject);
}
以上的代碼中藏鹊，不需要組個(gè)unreference source, sink, capsfilter. 由于它們都在pipleline中润讥，pipleline會自己處理好。如果手動處理盘寡，會報(bào)錯(cuò)誤楚殿。
最后，在修改class_init函數(shù)竿痰，將上邊的函數(shù)與gobject對象中定義的dispose與finalize函數(shù)bind起來：
static void
vcam_source_class_init(VcamSourceClass *kclass) {
//注冊私有屬性
......
/**memory manage**/
base_class->dispose = vcam_source_dispose;
base_class->finalize = vcam_source_finalize;
/* install properties */
......
}
測試代碼：
在.c文件中我們寫一個(gè)測試程序脆粥，創(chuàng)建一個(gè)新的vcamsource對象，并且啟動它影涉，然后獲取preroll sample, 如果獲取成功变隔，打印 ****：
int main(int argc, char* argv) {
gst_init(&argc, &argv);
g_print("start gst test\n");
VcamSource * source = g_object_new(VCAM_TYPE_SOURCE,NULL);
vcam_source_start(source);
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(source);
GstSample* sample;
sample = gst_app_sink_pull_preroll(priv->sink);
if(sample!=NULL)
g_print("*********\n");
g_print("start unrefercene \n");
g_object_unref(source);
g_print("program stop!!!!!!! \n");
}
上面的代碼包含了一行 gst_init(&argc, &argv);， 用于啟動gst系統(tǒng)蟹倾，它是我們上文提到的第一步的工作匣缘。測試打印結(jié)果如下：
image.png
完成代碼：
VcamSource.h
#ifndef VCAM_SOURCE_H
#define VCAM_SOURCE_H
#include <gst/gst.h>
#define VCAM_TYPE_SOURCE (vcam_source_get_type())
G_DECLARE_DERIVABLE_TYPE(VcamSource, vcam_source, VCAM, SOURCE, GObject)
typedef struct _VcamSourcePrivate VcamSourcePrivate;
struct _VcamSourceClass {
GObjectClass parent_class;
gshort(*start)(VcamSource* self);
};
gshort vcam_source_start(VcamSource* self);
void vcam_source_pull_sample(VcamSource* self, GstSample* sample);
void vcam_source_pull_preroll(VcamSource* self, GstSample* sample);
#endif /* __VCAM_SOURCE_H__ */
VcamSource.c
#include "VcamSource.h"
#include <gst/app/gstappsink.h>
struct _VcamSourcePrivate {
gboolean status;
GstElement* pipeline;
GstElement* source;
GstElement* capsfilter;
GstElement* sink;
};
G_DEFINE_TYPE_WITH_CODE(VcamSource, vcam_source, G_TYPE_OBJECT, G_ADD_PRIVATE(VcamSource) )
#define VCAM_SOURCE_GET_PRIVATE(obj) ( G_TYPE_INSTANCE_GET_PRIVATE((obj), VCAM_TYPE_SOURCE, VcamSourcePrivate))
enum _VCAM_SOURCE_PROPERTY {
VCAM_SOURCE_PROPERTY0,
VCAM_SOURCE_STATUS,
VCAM_SOURCE_VEDIO
};
static void vcam_source_finalize(GObject* gobject);
static void vcam_source_dispose(GObject* gobject);
static gshort startimpl(VcamSource* self);
static void vcam_source_set_property(GObject* object, guint property_id,
const GValue* value, GParamSpec* pspec);
static void vcam_source_get_property(GObject* object, guint property_id,
GValue* value, GParamSpec* pspec);
static void
vcam_source_class_init(VcamSourceClass* kclass) {
g_print("start the class init \n");
//注冊私有屬性
//g_type_class_add_private(kclass, sizeof(VcamSourcePriv));
kclass->start = startimpl;
/* override base object methods */
GObjectClass* base_class = G_OBJECT_CLASS(kclass);
base_class->set_property = vcam_source_set_property;
base_class->get_property = vcam_source_get_property;
/**memory manage**/
base_class->dispose = vcam_source_dispose;
base_class->finalize = vcam_source_finalize;
/* install properties */
// g_object_class_install_property(base_class, VCAM_SOURCE_STATUS,
// g_param_spec_uint("status", "source status", "desscribe server's status", \
// 0, 10, 0, G_PARAM_READWRITE));
}
static void
vcam_source_init(VcamSource* d) {
g_print("start the object init \n");
/* Create the elements */
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(d);
priv->source = gst_element_factory_make("videotestsrc", "source");
priv->sink = gst_element_factory_make("appsink", "app_sink");
priv->capsfilter = gst_element_factory_make("capsfilter", "caps_filter");
/* Create the empty pipeline */
priv->pipeline = gst_pipeline_new("test-pipeline");
if (!priv->pipeline || !priv->source || !priv->sink) {
g_printerr("Not all elements could be created.\n");
return;
}
/**設(shè)置 fitler caps**/
GstCaps* caps = gst_caps_new_simple("video/x-raw",
"format", G_TYPE_STRING, "I420",
"framerate", GST_TYPE_FRACTION, 25, 1,
"width", G_TYPE_INT, 320,
"height", G_TYPE_INT, 240,
NULL);
g_object_set(priv->capsfilter, "caps", caps, NULL);
/**設(shè)置appsink的max-buffers來限制buffer大小，設(shè)置drop屬性鲜棠，允許queue滿意后自動blockthread或drop舊的buffer**/
gst_app_sink_set_max_buffers(priv->sink, 500); // limit number of buffers queued
gst_app_sink_set_drop(priv->sink , TRUE); // drop old buffers in queue when full
/* Build the pipeline */
gst_bin_add_many(GST_BIN(priv->pipeline), priv->source, priv->capsfilter, priv->sink, NULL);
//if (gst_element_link(priv->source, priv->sink) != TRUE) {
if (gst_element_link(priv->source, priv->capsfilter) != TRUE || gst_element_link(priv->capsfilter, priv->sink) != TRUE) {
g_printerr("Elements could not be linked.\n");
gst_object_unref(priv->pipeline);
return -1;
}
}
//start pipleline
static gshort startimpl(VcamSource* self) {
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(self);
GstStateChangeReturn ret;
/* Start playing */
ret = gst_element_set_state(priv->pipeline, GST_STATE_PLAYING);
if (ret == GST_STATE_CHANGE_FAILURE) {
g_printerr("Unable to set the pipeline to the playing state (check the bus for error messages).\n");
return -1; //啟動失敗
}
else {
priv->status = TRUE;
return 0;
}
g_object_unref(priv); //結(jié)束引用
}
gshort vcam_source_start(VcamSource* self) {
VcamSourceClass* klass = VCAM_SOURCE_GET_CLASS(self);
if (klass->start == NULL) return -2; //函數(shù)未初始化
return klass->start(self);
g_object_unref(klass); //結(jié)束引用
}
static void
vcam_source_set_property(GObject* object, guint property_id,
const GValue* value, GParamSpec* pspec)
{
VcamSource* self = VCAM_SOURCE(object);
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(self);
switch (property_id) {
case VCAM_SOURCE_STATUS:
priv->status = g_value_get_boolean(value);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);
break;
}
g_object_unref(self); //結(jié)束引用
g_object_unref(priv); //結(jié)束引用
}
static void
vcam_source_get_property(GObject* object, guint property_id,
GValue* value, GParamSpec* pspec)
{
VcamSource* self = VCAM_SOURCE(object);
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(self);
switch (property_id) {
case VCAM_SOURCE_STATUS:
g_value_set_boolean(value, priv->status);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);
break;
}
g_object_unref(self); //結(jié)束引用
g_object_unref(priv); //結(jié)束引用
}
void vcam_source_pull_sample(VcamSource* self, GstSample* sample) {
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(self);
g_return_if_fail(priv->sink != NULL);
sample = gst_app_sink_pull_sample(priv->sink);
if (sample == NULL && gst_app_sink_is_eos(priv->sink)) {
g_print("the stream reach the ond \n");
sample = NULL;
//send out singal for eof of stream
}
else
{
g_print("gst_app_sink_pull_sample returned null\n");
sample = NULL;
return NULL;
}
g_object_unref(priv); //結(jié)束引用
}
void vcam_source_pull_preroll(VcamSource* self, GstSample* sample) {
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(self);
g_return_if_fail(priv->sink != NULL);
sample = gst_app_sink_pull_preroll(priv->sink);
if (sample == NULL && gst_app_sink_is_eos(priv->sink)) {
g_print("the stream reach the ond \n");
//send out singal for eof of stream
}
else {
g_print("gst_app_sink_pull_preroll returned null\n");
}
g_object_unref(priv); //結(jié)束引用
}
static void
vcam_source_dispose(GObject* gobject)
{
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(gobject);
/* In dispose(), you are supposed to free all types referenced from this
* object which might themselves hold a reference to self. Generally,
* the most simple solution is to unref all members on which you own a
* reference.
*/
/* dispose() might be called multiple times, so we must guard against
* calling g_object_unref() on an invalid GObject by setting the member
* NULL; g_clear_object() does this for us.
*/
gst_element_set_state(priv->pipeline, GST_STATE_NULL);
//source, capsfitler, sink 都有pipeline 管理肌厨， 清除工作有pipleline來完成
g_clear_object(&priv->pipeline);
/* Always chain up to the parent class; there is no need to check if
* the parent class implements the dispose() virtual function: it is
* always guaranteed to do so
*/
G_OBJECT_CLASS(vcam_source_parent_class)->dispose(gobject);
}
static void
vcam_source_finalize(GObject* gobject)
{
VcamSourcePrivate * priv = VCAM_SOURCE_GET_PRIVATE(gobject);
/* Always chain up to the parent class; as with dispose(), finalize()
* is guaranteed to exist on the parent's class virtual function table
*/
G_OBJECT_CLASS(vcam_source_parent_class)->finalize(gobject);
}
int main(int argc, char* argv) {
gst_init(&argc, &argv);
g_print("start gst test\n");
VcamSource * source = g_object_new(VCAM_TYPE_SOURCE,NULL);
vcam_source_start(source);
VcamSourcePrivate* priv = VCAM_SOURCE_GET_PRIVATE(source);
GstSample* sample;
sample = gst_app_sink_pull_preroll(priv->sink);
if(sample!=NULL)
g_print("*********\n");
g_print("start unrefercene \n");
g_object_unref(source);
g_print("program stop!!!!!!! \n");
}
