Gstreamer elements

gstream have several type of element : source, sink, transform, filter, mixer

sources : videtestsrc, rtsp sink : autovideosink, fakesink transform: videoconvert, codec filter : set bitrate, scale , crop, overlay

Basic concepts

Pipeline: A pipeline is a sequence of elements connected together, which together define a media processing flow.

Element: An element is a unit of processing in GStreamer, such as a video source or a video filter. Elements have pads that connect to other elements in the pipeline.

Pad: A pad is a logical endpoint of an element that connects to other elements in the pipeline, enabling data to be sent and received between elements.

Bin: A bin is a container for elements, used to organize and encapsulate elements within a pipeline.

Plugin: A plugin is a loadable module that provides one or more GStreamer elements, such as a video decoder or an audio encoder.

Caps: Caps is short for “capabilities” and describes the media format and properties of data flowing through a pipeline.

Pipeline state: The pipeline state describes whether a pipeline is running, paused, or stopped.

Bus: The bus is a message passing mechanism used to notify applications about events in the pipeline, such as errors or state changes.

Create a transform or filter element

It can be done by

• create a probe function with gst_pad_add_probe by register probe with the element pad ( called when data come to the pad )

• create transform element and register transform_ip function code (called when data flow come in the plugin)

• create chain callback ( is called when a new sample come in)

Notes

need to understand what type of image is processing (RGBA, RGB, YUVI,..)

GstPad* pad = gst_element_get_static_pad(videotestsrc, "src");
GstCaps* caps = gst_pad_get_current_caps(pad);

if (caps) {
  GstVideoInfo info;
  if (gst_video_info_from_caps(&info, caps)) {
    g_print("Video format: %dx%d, framerate=%d/%d, format=%s\n",
            GST_VIDEO_INFO_WIDTH(&info), GST_VIDEO_INFO_HEIGHT(&info),
            GST_VIDEO_INFO_FPS_N(&info), GST_VIDEO_INFO_FPS_D(&info),
            gst_video_format_to_string(GST_VIDEO_INFO_FORMAT(&info)));
  }

  gst_caps_unref(caps);
}

gst_object_unref(pad);