gstreamer实现一个编码插件

要实现一个gstreamer编码插件，你需要遵循以下步骤：

1. 定义插件的元数据：在插件的源代码中定义元数据，如插件的名字、类型、作者、版本号等。

2. 实现插件的结构：定义插件的类和结构体，包括源代码文件、头文件、库文件和插件模板。

3. 实现插件的功能：在插件结构中定义编码器的功能，包括输入数据的格式、编码参数等。

4. 编译和安装插件：将插件源代码编译成共享库文件，并将其安装到gstreamer插件目录中。

以下是一个简单的gstreamer编码插件示例：

#include <gst/gst.h>
#include <string.h>

GST_DEBUG_CATEGORY_STATIC (myencoder_debug);
#define GST_CAT_DEFAULT myencoder_debug

#define GST_TYPE_MYENCODER \
  (myencoder_get_type())
#define GST_MYENCODER(obj) \
  (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_MYENCODER,MyEncoder))
#define GST_MYENCODER_CLASS(klass) \
  (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_MYENCODER,MyEncoderClass))
#define GST_IS_MYENCODER(obj) \
  (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_MYENCODER))
#define GST_IS_MYENCODER_CLASS(klass) \
  (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_MYENCODER))

typedef struct _MyEncoder MyEncoder;
typedef struct _MyEncoderClass MyEncoderClass;

struct _MyEncoder {
  GstElement element;
  GstPad *sinkpad, *srcpad;
  gboolean silent;
};

struct _MyEncoderClass {
  GstElementClass parent_class;
};

GType myencoder_get_type (void);

static void myencoder_set_property (GObject * object, guint prop_id, const GValue * value, GParamSpec * pspec);
static void myencoder_get_property (GObject * object, guint prop_id, GValue * value, GParamSpec * pspec);
static GstFlowReturn myencoder_chain (GstPad * pad, GstObject * parent, GstBuffer * buf);
static gboolean myencoder_sink_event (GstPad * pad, GstObject * parent, GstEvent * event);
static gboolean myencoder_src_event (GstPad * pad, GstObject * parent, GstEvent * event);
static void myencoder_finalize (GObject * object);

#define MYENCODER_PROP_SILENT 1

#define gst_myencoder_parent_class parent_class
G_DEFINE_TYPE (MyEncoder, myencoder, GST_TYPE_ELEMENT);

static void
myencoder_class_init (MyEncoderClass * klass)
{
  GObjectClass *gobject_class;
  GstElementClass *gstelement_class;

  gobject_class = (GObjectClass *) klass;
  gstelement_class = (GstElementClass *) klass;

  gobject_class->set_property = myencoder_set_property;
  gobject_class->get_property = myencoder_get_property;

  g_object_class_install_property (gobject_class, MYENCODER_PROP_SILENT,
      g_param_spec_boolean ("silent", "Silent", "Produce verbose output ?",
          FALSE, G_PARAM_READWRITE));

  gstelement_class->sink_event = GST_DEBUG_FUNCPTR (myencoder_sink_event);
  gstelement_class->src_event = GST_DEBUG_FUNCPTR (myencoder_src_event);
  gstelement_class->finalize = GST_DEBUG_FUNCPTR (myencoder_finalize);

  gst_element_class_set_static_metadata (gstelement_class,
      "My Encoder", "Codec/Encoder",
      "Encode data using a custom algorithm", "Your Name <email@example.com>");
}

static void
myencoder_init (MyEncoder * filter)
{
  filter->sinkpad = gst_pad_new_from_static_template (&sink_template, "sink");
  gst_pad_set_chain_function (filter->sinkpad, myencoder_chain);
  gst_pad_set_event_function (filter->sinkpad, GST_DEBUG_FUNCPTR (gst_pad_event_default));
  GST_PAD_SET_PROXY_CAPS (filter->sinkpad);
  gst_element_add_pad (GST_ELEMENT (filter), filter->sinkpad);

  filter->srcpad = gst_pad_new_from_static_template (&src_template, "src");
  gst_pad_use_fixed_caps (filter->srcpad);
  gst_element_add_pad (GST_ELEMENT (filter), filter->srcpad);

  filter->silent = FALSE;
}

static void
myencoder_set_property (GObject * object, guint prop_id, const GValue * value, GParamSpec * pspec)
{
  MyEncoder *filter = GST_MYENCODER (object);

  switch (prop_id) {
    case MYENCODER_PROP_SILENT:
      filter->silent = g_value_get_boolean (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
myencoder_get_property (GObject * object, guint prop_id, GValue * value, GParamSpec * pspec)
{
  MyEncoder *filter = GST_MYENCODER (object);

  switch (prop_id) {
    case MYENCODER_PROP_SILENT:
      g_value_set_boolean (value, filter->silent);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static gboolean
myencoder_sink_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
  MyEncoder *filter;
  gboolean ret;

  filter = GST_MYENCODER (parent);

  GST_LOG_OBJECT (filter, "Received %s event: %" GST_PTR_FORMAT,
      GST_EVENT_TYPE_NAME (event), event);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_CAPS:
      /* we should handle the format here */
      ret = gst_pad_event_default (pad, parent, event);
      break;
    default:
      ret = gst_pad_event_default (pad, parent, event);
      break;
  }
  return ret;
}

static gboolean
myencoder_src_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
  MyEncoder *filter;
  gboolean ret;

  filter = GST_MYENCODER (parent);

  GST_LOG_OBJECT (filter, "Received %s event: %" GST_PTR_FORMAT,
      GST_EVENT_TYPE_NAME (event), event);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_CAPS:
      /* we should fixate the caps here */
      ret = gst_pad_event_default (pad, parent, event);
      break;
    default:
      ret = gst_pad_event_default (pad, parent, event);
      break;
  }
  return ret;
}

static GstFlowReturn
myencoder_chain (GstPad * pad, GstObject * parent, GstBuffer * buf)
{
  MyEncoder *filter;

  filter = GST_MYENCODER (parent);

  if (filter->silent == FALSE)
    g_print ("I'm plugged, therefore I'm in.\n");

  /* just push out the incoming buffer without touching it */
  return gst_pad_push (filter->srcpad, buf);
}

static void
myencoder_finalize (GObject * object)
{
  MyEncoder *filter = GST_MYENCODER (object);

  gst_object_unref (filter->sinkpad);
  gst_object_unref (filter->srcpad);

  G_OBJECT_CLASS (myencoder_parent_class)->finalize (object);
}

static GType
myencoder_get_type (void)
{
  static GType myencoder_type = 0;

  if (!myencoder_type) {
    static const GTypeInfo myencoder_info = {
      sizeof (MyEncoderClass),
      NULL,   /* base_init */
      NULL,   /* base_finalize */
      (GClassInitFunc) myencoder_class_init,
      NULL,   /* class_finalize */
      NULL,   /* class_data */
      sizeof (MyEncoder),
      0,      /* n_preallocs */
      (GInstanceInitFunc) myencoder_init,
      NULL    /* value_table */
    };

    myencoder_type = g_type_register_static (GST_TYPE_ELEMENT, "MyEncoder",
        &myencoder_info, 0);
  }

  return myencoder_type;
}

在这个示例中，我们实现了一个简单的编码插件，其中包括一个sinkpad和一个srcpad，用于接收和传输数据。当数据到达sinkpad时，插件将其编码并通过srcpad发送出去。当编码器启动时，它会输出一条消息。

要使用这个插件，你需要将它编译成共享库文件（.so或.dll），并将其安装到gstreamer插件目录中。然后，你可以使用gst-launch或其他gstreamer工具来测试你的编码器插件。