gstreamer plug-knowledge summary

gstreamer plug-knowledge summary

1.gstreamer plug internal structure and function summary

(1) define plug-in properties and the signal

enum
{
  /* FILL ME */
  SIGNAL_DETECTED,
  LAST_SIGNAL
};

(2) the gasket defines the type of data transmitted and received

static GstStaticPadTemplate sink_factory...

(3) elements and attributes initialization signal

gst_human_detection_class_init()

Attribute initialization sample:

g_object_class_install_property (gobject_class, PROP_PICTUREPATH,
      g_param_spec_string ("picturePath", "picturePath", "output picturePath",
          "NULL", (GParamFlags)(G_PARAM_WRITABLE | G_PARAM_STATIC_STRINGS)));

Sample initialization signal:

gst_human_detection_signals[SIGNAL_DETECTED] =
			g_signal_new ("detected", G_TYPE_FROM_CLASS (klass), G_SIGNAL_RUN_LAST,
            G_STRUCT_OFFSET (GstHumanDetectionClass, detected), NULL, NULL,
            g_cclosure_marshal_VOID__POINTER, G_TYPE_NONE, 1, G_TYPE_POINTER);

(4) element is initialized (initialization when loading or element)

gst_human_detection_init()

Stored in a function such as loading only loaded once without loading the cycle times and events networks.

(5) Function Set Properties

gst_human_detection_set_property()

(6) property getters

gst_human_detection_get_property()

(7) a main function operation (video stream goes through each frame of the image processing function)

gst_human_detection_chain()

2. Internal plug-in uses knowledge

(1) the use of locks

pthread_mutex_t threadMutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_lock(&threadMutex);
pthread_mutex_unlock(&threadMutex);

(2) an initialization signal

static guint gst_human_detection_signals[LAST_SIGNAL] = { 0 };

(3) obtaining resolution video stream

int width, height;
GstCaps *caps;
caps = gst_pad_get_current_caps (pad);
GstStructure* structure = gst_caps_get_structure(caps, 0);

gst_structure_get_int(structure, "width", &width);
gst_structure_get_int(structure, "height", &height);
...
gst_caps_unref (caps);

(4) obtaining a video image of each frame

GstMapInfo map;
gst_buffer_map(buf, &map, GST_MAP_READ);
v = Mat(Size(width,height),CV_8UC4,(char *)map.data);
...
memcpy(map.data, v.data, map.size);
gst_buffer_unmap (buf, &map);