我正在尝试执行以下操作:使用 gstreamer 接收视频流并使用 opencv 处理它。我找到了几个解决方案，其中之一是将视频写入(来自gstreamer)fifo，然后使用opencv读取它。 (此处的选项 3 MJPEG streaming and decoding)。问题是我打不开管道。 cvCreateFileCapture 永远不会返回。这是我写的部分代码:

if(mkfifo("fifo.avi", S_IRUSR| S_IWUSR) == -1)
{
    cout<<"Cant create fifo"<<endl;
    cout<<errno<<endl;
}

loop = g_main_loop_new(NULL, false);

fsink = gst_element_factory_make("filesink", "fsink");
g_object_set(G_OBJECT(fsink), "location", "fifo.avi", NULL);

playbin = gst_element_factory_make("playbin2", "play");    
g_object_set(G_OBJECT(playbin), "uri", uri.c_str(), NULL);
g_object_set(G_OBJECT(playbin), "video-sink", fsink, NULL);

bus = gst_pipeline_get_bus(GST_PIPELINE(playbin));
gst_bus_add_signal_watch(bus);

g_signal_connect(bus, "message::buffering", G_CALLBACK(&set_playbin_state), playbin);
gst_object_unref(bus);

cvNamedWindow("output", CV_WINDOW_AUTOSIZE);
capture = cvCreateFileCapture("fifo.avi");

程序堆栈在最后一行。 PS:我使用的是opencv 2.3.1。

最佳答案

这是我针对 Gstreamer 1.4.0 和 OpenCV 2.4.9 的完整源代码解决方案。

它使用 gst_parse_launch() 来解析您将提供给 gst-launch 的普通命令行。 Gstreamer 管道将帧转换为 RGB888 格式，然后再将其输入 OpenCV，以便尽可能轻松地进行转换。

OpenCV 帧处理不在 new_sample() 回调中完成，但它只从 gstreamer 抓取帧并将其推送到队列，然后将在主线程中使用。这样我们就可以调用例如来自 OpenCV 的 imshow() 将图像实际渲染到屏幕。

~150 行...通过删除调试打印等可以减少到 <100>

可能应该在双端队列读/写周围添加线程同步

#include <gst/gst.h>
#include <gst/app/gstappsink.h>
#include <stdlib.h>

#include "opencv2/opencv.hpp"
using namespace cv;

// TODO: use synchronized deque
std::deque<Mat> frameQueue;

GstFlowReturn
new_preroll(GstAppSink *appsink, gpointer data) {
  g_print ("Got preroll!\n");
  return GST_FLOW_OK;
}

GstFlowReturn
new_sample(GstAppSink *appsink, gpointer data) {
  static int framecount = 0;
  framecount++;

  GstSample *sample = gst_app_sink_pull_sample(appsink);
  GstCaps *caps = gst_sample_get_caps(sample);
  GstBuffer *buffer = gst_sample_get_buffer(sample);
  const GstStructure *info = gst_sample_get_info(sample);

  // ---- Read frame and convert to opencv format ---------------

  GstMapInfo map;
  gst_buffer_map (buffer, &map, GST_MAP_READ);

  // convert gstreamer data to OpenCV Mat, you could actually
  // resolve height / width from caps...
  Mat frame(Size(320, 240), CV_8UC3, (char*)map.data, Mat::AUTO_STEP);
  int frameSize = map.size;

  // TODO: synchronize this....
  frameQueue.push_back(frame);

  gst_buffer_unmap(buffer, &map);

  // ------------------------------------------------------------

  // print dot every 30 frames
  if (framecount%30 == 0) {
    g_print (".");
  }

  // show caps on first frame
  if (framecount == 1) {
    g_print ("%s\n", gst_caps_to_string(caps));
  }

  gst_sample_unref (sample);
  return GST_FLOW_OK;
}

static gboolean
my_bus_callback (GstBus *bus, GstMessage *message, gpointer data) {
  g_print ("Got %s message\n", GST_MESSAGE_TYPE_NAME (message));
  switch (GST_MESSAGE_TYPE (message)) {
    case GST_MESSAGE_ERROR: {
      GError *err;
      gchar *debug;

      gst_message_parse_error (message, &err, &debug);
      g_print ("Error: %s\n", err->message);
      g_error_free (err);
      g_free (debug);    
      break;
    }
    case GST_MESSAGE_EOS:
      /* end-of-stream */
      break;
    default:
      /* unhandled message */
      break;
  }
  /* we want to be notified again the next time there is a message
   * on the bus, so returning TRUE (FALSE means we want to stop watching
   * for messages on the bus and our callback should not be called again)
   */
  return TRUE;
}

int
main (int argc, char *argv[])
{
  GError *error = NULL;

  gst_init (&argc, &argv);

  gchar *descr = g_strdup(
    "videotestsrc  pattern=ball ! "
    "video/x-raw,format=RGB ! "
    "videoconvert ! "
    "appsink name=sink sync=true"
  );
  GstElement *pipeline = gst_parse_launch (descr, &error);

  if (error != NULL) {
    g_print ("could not construct pipeline: %s\n", error->message);
    g_error_free (error);
    exit (-1);
  }

  /* get sink */
  GstElement *sink = gst_bin_get_by_name (GST_BIN (pipeline), "sink");

  gst_app_sink_set_emit_signals((GstAppSink*)sink, true);
  gst_app_sink_set_drop((GstAppSink*)sink, true);
  gst_app_sink_set_max_buffers((GstAppSink*)sink, 1);
  GstAppSinkCallbacks callbacks = { NULL, new_preroll, new_sample };
  gst_app_sink_set_callbacks (GST_APP_SINK(sink), &callbacks, NULL, NULL);

  GstBus *bus;
  guint bus_watch_id;
  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  bus_watch_id = gst_bus_add_watch (bus, my_bus_callback, NULL);
  gst_object_unref (bus);

  gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);

  namedWindow("edges",1);
  while(1) {
    g_main_iteration(false);

      // TODO: synchronize...
    if (frameQueue.size() > 0) {
      // this lags pretty badly even when grabbing frames from webcam
      Mat frame = frameQueue.front();
      Mat edges;
      cvtColor(frame, edges, CV_RGB2GRAY);
      GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
      Canny(edges, edges, 0, 30, 3);
      imshow("edges", edges);
      cv::waitKey(30);
      frameQueue.clear();
    }
  }  

  gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
  gst_object_unref (GST_OBJECT (pipeline));

  return 0;  
}

要在 OSX/Linux 上编译这样的 make 文件应该这样做:

GST_FLAGS=$(shell pkg-config --cflags --libs gstreamer-gl-1.0 gstreamer-tag-1.0 gstreamer-net-1.0 gstreamer-sdp-1.0 \
  gstreamer-1.0 gstreamer-allocators-1.0 gstreamer-insertbin-1.0 gstreamer-plugins-base-1.0 \
  gstreamer-codecparsers-1.0 gstreamer-base-1.0 gstreamer-app-1.0 gstreamer-check-1.0 \
  gstreamer-controller-1.0 gstreamer-video-1.0 gstreamer-fft-1.0 gstreamer-mpegts-1.0 \
  gstreamer-pbutils-1.0 gstreamer-rtp-1.0 gstreamer-rtsp-1.0 \
  gstreamer-riff-1.0 gstreamer-audio-1.0 gstreamer-plugins-bad-1.0 opencv)

OPENCV_FLAGS=$(shell pkg-config --cflags --libs opencv)

all: gst_opencv

gst_opencv: gst_opencv
    g++ $(GST_FLAGS) $(OPENCV_FLAGS) gst_opencv -o gst_opencv

clean:
    rm -f gst_opencv

关于c++ - 将 opencv 处理添加到 gstreamer 应用程序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10403588/