Gstreamer 기본 튜토리얼 01: Hello world!

목표

video를 재생시켜본다.

basic-tutorial-1.c

#include <gst/gst.h>

int
main (int argc, char *argv[])
{
  GstElement *pipeline;
  GstBus *bus;
  GstMessage *msg;

  /* Initialize GStreamer */
  gst_init (&argc, &argv);

  /* Build the pipeline */
  pipeline =
      gst_parse_launch
      ("playbin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm",
      NULL);

  /* Start playing */
  gst_element_set_state (pipeline, GST_STATE_PLAYING);

  /* Wait until error or EOS */
  bus = gst_element_get_bus (pipeline);
  msg =
      gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
      GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

  /* Free resources */
  if (msg != NULL)
    gst_message_unref (msg);
  gst_object_unref (bus);
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);
  return 0;
}

빌드

리눅스의 경우 아래와 같이 하면 된다.

gcc basic-tutorial-1.c -o basic-tutorial-1 `pkg-config --cflags --libs gstreamer-1.0`

자세한 정보는 아래를 참고한다.

• Linux
• Mac OS X
• Windows

분석

gst_init

/* Initialize GStreamer */
gst_init (&argc, &argv);

처음에는 gst_init()을 호출하여 초기화를 해준다.

gst_parse_lauch

/* Build the pipeline */
pipeline =
    gst_parse_launch
    ("playbin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm",
    NULL);

Gstreamer에서 파이프라인은 각 엘리먼트들을 조합해야하지만, 파이프라인이 간단하다면 gst_parse_launch()로 쉽게 만들 수 있다.

playbin

playbin은 특별한 엘리먼트로 내부적으로 필요한 엘리먼트들을 연결한다.

/* Start playing */
gst_element_set_state (pipeline, GST_STATE_PLAYING);

Gstreamer 엘리먼트는 상태를 가지고 있으며, gst_element_set_state로 GST_STATE_PLAYING 상태로 변경한다.

/* Wait until error or EOS */
bus = gst_element_get_bus (pipeline);
msg =
    gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
    GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

gst_element_get_bus()는 파이프라인의 버스를 얻고, gst_bus_timed_pop_filtered()는 버스로부터 ERROR나 EOS를 얻기 전까지 블록된다.

cleanup

/* Free resources */
if (msg != NULL)
  gst_message_unref (msg);
gst_object_unref (bus);
gst_element_set_state (pipeline, GST_STATE_NULL);
gst_object_unref (pipeline);

gst_bus_timed_pop_filtered()로 얻은 메시지를 gst_message_unref()로 해제한다.
gst_element_get_bus()로 얻은 버스를 gst_object_unref()로 해제한다.
파이프라인을 GST_STATE_NULL 상태로 설정하고, 파이프라인과 내부의 엘리먼트들을 gst_object_unref()로 해제한다.

참고사이트

Basic tutorial 1: Hello world!

LICENSE

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