uvc_cam.cpp

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/* This file is from the uvc_cam package by Morgan Quigley */
#include <cstring>
#include <string>
#include <cstdio>
#include <stdexcept>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include "uvc_cam/uvc_cam.h"
#include <unistd.h>

#ifndef INT64_C
#define INT64_C(c) (c ## LL)
#define UINT64_C(c) (c ## ULL)
#endif

extern "C" {
#include <linux/videodev2.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}

static AVFrame *avframe_camera = NULL;
static AVFrame *avframe_rgb = NULL;
static AVCodec *avcodec = NULL;
static AVCodecContext *avcodec_context = NULL;
static int avframe_camera_size = 0;
static int avframe_rgb_size = 0;
struct SwsContext *video_sws = NULL;
unsigned char* jpegBuf = NULL;

using std::string;
using namespace uvc_cam;

Cam::Cam(const char *_device, mode_t _mode, int _width, int _height, int _fps)
: mode(_mode), device(_device),
  motion_threshold_luminance(100), motion_threshold_count(-1),
  width(_width), height(_height), fps(_fps), rgb_frame(NULL)
{
  printf("opening %s\n", _device);
  if ((fd = open(_device, O_RDWR)) == -1)
    throw std::runtime_error("couldn't open " + device);
  memset(&fmt, 0, sizeof(v4l2_format));
  memset(&cap, 0, sizeof(v4l2_capability));
  if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0)
    throw std::runtime_error("couldn't query " + device);
  if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
    throw std::runtime_error(device + " does not support capture");
  if (!(cap.capabilities & V4L2_CAP_STREAMING))
    throw std::runtime_error(device + " does not support streaming");
  // enumerate formats
  v4l2_fmtdesc f;
  memset(&f, 0, sizeof(f));
  f.index = 0;
  f.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  int ret;
  while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &f)) == 0)
  {
    printf("pixfmt %d = '%4s' desc = '%s'\n",
           f.index++, (char *)&f.pixelformat, f.description);
    // enumerate frame sizes
    v4l2_frmsizeenum fsize;
    fsize.index = 0;
    fsize.pixel_format = f.pixelformat;
    while ((ret = ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &fsize)) == 0)
    {
      fsize.index++;
      if (fsize.type == V4L2_FRMSIZE_TYPE_DISCRETE)
      {
        printf("  discrete: %ux%u:   ",
               fsize.discrete.width, fsize.discrete.height);
        // enumerate frame rates
        v4l2_frmivalenum fival;
        fival.index = 0;
        fival.pixel_format = f.pixelformat;
        fival.width = fsize.discrete.width;
        fival.height = fsize.discrete.height;
        while ((ret = ioctl(fd, VIDIOC_ENUM_FRAMEINTERVALS, &fival)) == 0)
        {
          fival.index++;
          if (fival.type == V4L2_FRMIVAL_TYPE_DISCRETE)
          {
            printf("%u/%u ",
                   fival.discrete.numerator, fival.discrete.denominator);
          }
          else
            printf("I only handle discrete frame intervals...\n");
        }
        printf("\n");
      }
      else if (fsize.type == V4L2_FRMSIZE_TYPE_CONTINUOUS)
      {
        printf("  continuous: %ux%u to %ux%u\n",
               fsize.stepwise.min_width, fsize.stepwise.min_height,
               fsize.stepwise.max_width, fsize.stepwise.max_height);
      }
      else if (fsize.type == V4L2_FRMSIZE_TYPE_STEPWISE)
      {
        printf("  stepwise: %ux%u to %ux%u step %ux%u\n",
               fsize.stepwise.min_width,  fsize.stepwise.min_height,
               fsize.stepwise.max_width,  fsize.stepwise.max_height,
               fsize.stepwise.step_width, fsize.stepwise.step_height);
      }
      else
      {
        printf("  fsize.type not supported: %d\n", fsize.type);
      }
    }
  }
  if (errno != EINVAL)
    throw std::runtime_error("error enumerating frame formats");
  fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  fmt.fmt.pix.width = width;
  fmt.fmt.pix.height = height;
  if (mode == MODE_RGB || mode == MODE_YUYV) // we'll convert later
    fmt.fmt.pix.pixelformat = 'Y' | ('U' << 8) | ('Y' << 16) | ('V' << 24);
  else
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
  fmt.fmt.pix.field = V4L2_FIELD_ANY;
  if ((ret = ioctl(fd, VIDIOC_S_FMT, &fmt)) < 0)
    throw std::runtime_error("couldn't set format");
  if (fmt.fmt.pix.width != width || fmt.fmt.pix.height != height)
    throw std::runtime_error("pixel format unavailable");
  streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  streamparm.parm.capture.timeperframe.numerator = 1;
  streamparm.parm.capture.timeperframe.denominator = fps;
  if ((ret = ioctl(fd, VIDIOC_S_PARM, &streamparm)) < 0)
    throw std::runtime_error("unable to set framerate");
  v4l2_queryctrl queryctrl;
  memset(&queryctrl, 0, sizeof(queryctrl));
  uint32_t i = V4L2_CID_BASE;
  while (i != V4L2_CID_LAST_EXTCTR)
  {
    queryctrl.id = i;
    if ((ret = ioctl(fd, VIDIOC_QUERYCTRL, &queryctrl)) == 0 &&
        !(queryctrl.flags & V4L2_CTRL_FLAG_DISABLED))
    {
      const char *ctrl_type = NULL;
      if (queryctrl.type == V4L2_CTRL_TYPE_INTEGER)
        ctrl_type = "int";
      else if (queryctrl.type == V4L2_CTRL_TYPE_BOOLEAN)
        ctrl_type = "bool";
      else if (queryctrl.type == V4L2_CTRL_TYPE_BUTTON)
        ctrl_type = "button";
      else if (queryctrl.type == V4L2_CTRL_TYPE_MENU)
        ctrl_type = "menu";
      printf("  %s (%s, %d, id = %x): %d to %d (%d)\n",
             ctrl_type,
             queryctrl.name, queryctrl.flags, queryctrl.id,
             queryctrl.minimum, queryctrl.maximum, queryctrl.step);
      if (queryctrl.type == V4L2_CTRL_TYPE_MENU)
      {
        v4l2_querymenu querymenu;
        memset(&querymenu, 0, sizeof(querymenu));
        querymenu.id = queryctrl.id;
        querymenu.index = 0;
        while (ioctl(fd, VIDIOC_QUERYMENU, &querymenu) == 0)
        {
          printf("    %d: %s\n", querymenu.index, querymenu.name);
          querymenu.index++;
        }
      }

    }
    else if (errno != EINVAL)
      throw std::runtime_error("couldn't query control");
    i++;
    if (i == V4L2_CID_LAST_NEW)
      i = V4L2_CID_CAMERA_CLASS_BASE_NEW;
    else if (i == V4L2_CID_CAMERA_CLASS_LAST)
      i = V4L2_CID_PRIVATE_BASE_OLD;
    else if (i == V4L2_CID_PRIVATE_LAST)
      i = V4L2_CID_BASE_EXTCTR;
  }

  try
  {
    // the commented labels correspond to the controls in guvcview and uvcdynctrl  

        set_control(V4L2_CID_EXPOSURE_AUTO, 3);
    set_control(0x009a0903, 1);
   // set_control(10094851, 1); // Exposure, Auto Priority
  //  set_control(10094849, 1); // Exposure, Auto
  //  set_control(168062321, 0); //Disable video processing
  //  set_control(0x9a9010, 100);
  //  set_control(V4L2_CID_EXPOSURE_ABSOLUTE_NEW, 300);
    set_control(V4L2_CID_BRIGHTNESS, 140);
    set_control(V4L2_CID_CONTRAST, 40);
    set_control(V4L2_CID_AUTO_WHITE_BALANCE, 1);
    set_control(V4L2_CID_GAIN, 120);
    set_control(V4L2_CID_SHARPNESS, 140);
    set_control(V4L2_CID_SATURATION, 45);
 //   set_control(V4L2_CID_WHITE_BALANCE_TEMP_AUTO_OLD, 0);
  //  set_control(9963776, 128); //Brightness
  //  set_control(9963777, 32); //Contrast
  //  set_control(9963788, 1); // White Balance Temperature, Auto
  //  set_control(9963802, 5984); // White Balance Temperature
  //  set_control(9963800, 2);  // power line frequency to 60 hz
//    set_control(9963795, 200); // Gain
//    set_control(9963803, 224); // Sharpness
 //   set_control(9963804, 1); //Backlight Compensation
 //  set_control(10094850, 250); // Exposure (Absolute)
 //   set_control(168062212, 16); //Focus (absolute)
 //   set_control(168062213, 3); //LED1 Mode
 //   set_control(168062214, 0); //LED1 Frequency
    set_control(9963778, 32); // Saturation
  }
  catch (std::runtime_error &ex)
  {
    printf("ERROR: could not set some settings.  \n %s \n", ex.what());
  }

/*
  v4l2_jpegcompression v4l2_jpeg;
  if (ioctl(fd, VIDIOC_G_JPEGCOMP, &v4l2_jpeg) < 0)
    throw std::runtime_error("no jpeg compression iface exposed");
  printf("jpeg quality: %d\n", v4l2_jpeg.quality);
*/

  memset(&rb, 0, sizeof(rb));
  rb.count = NUM_BUFFER;
  rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  rb.memory = V4L2_MEMORY_MMAP;
  if (ioctl(fd, VIDIOC_REQBUFS, &rb) < 0)
    throw std::runtime_error("unable to allocate buffers");
  for (unsigned i = 0; i < NUM_BUFFER; i++)
  {
    memset(&buf, 0, sizeof(buf));
    buf.index = i;
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.flags = V4L2_BUF_FLAG_TIMECODE;
    buf.timecode = timecode;
    buf.timestamp.tv_sec = 0;
    buf.timestamp.tv_usec = 0;
    buf.memory = V4L2_MEMORY_MMAP;
    if (ioctl(fd, VIDIOC_QUERYBUF, &buf) < 0)
      throw std::runtime_error("unable to query buffer");
    if (buf.length <= 0)
      throw std::runtime_error("buffer length is bogus");
    mem[i] = mmap(0, buf.length, PROT_READ, MAP_SHARED, fd, buf.m.offset);
    //printf("buf length = %d at %x\n", buf.length, mem[i]);
    if (mem[i] == MAP_FAILED)
      throw std::runtime_error("couldn't map buffer");
  }
  buf_length = buf.length;
  for (unsigned i = 0; i < NUM_BUFFER; i++)
  {
    memset(&buf, 0, sizeof(buf));
    buf.index = i;
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.flags = V4L2_BUF_FLAG_TIMECODE;
    buf.timecode = timecode;
    buf.timestamp.tv_sec = 0;
    buf.timestamp.tv_usec = 0;
    buf.memory = V4L2_MEMORY_MMAP;
    if (ioctl(fd, VIDIOC_QBUF, &buf) < 0)
      throw std::runtime_error("unable to queue buffer");
  }
  int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  if (ioctl(fd, VIDIOC_STREAMON, &type) < 0)
    throw std::runtime_error("unable to start capture");
  rgb_frame = new unsigned char[width * height * 3];
  last_yuv_frame = new unsigned char[width * height * 2];


  init_mjpeg_decoder(width, height);
  jpegBuf = (unsigned char*) malloc(width*height*3);
}

Cam::~Cam()
{
  // stop stream
  int type = V4L2_BUF_TYPE_VIDEO_CAPTURE, ret;
  if ((ret = ioctl(fd, VIDIOC_STREAMOFF, &type)) < 0)
    perror("VIDIOC_STREAMOFF");
  for (unsigned i = 0; i < NUM_BUFFER; i++)
    if (munmap(mem[i], buf_length) < 0)
      perror("failed to unmap buffer");
  close(fd);
  if (rgb_frame)
  {
    delete[] rgb_frame;
    delete[] last_yuv_frame;
  }
  last_yuv_frame = rgb_frame = NULL;

  if(jpegBuf)
    free(jpegBuf);
}

void Cam::enumerate()
{
  string v4l_path = "/sys/class/video4linux";
  DIR *d = opendir(v4l_path.c_str());
  if (!d)
    throw std::runtime_error("couldn't open " + v4l_path);
  struct dirent *ent, *ent2, *ent3;
  int fd, ret;
  struct v4l2_capability v4l2_cap;
  while ((ent = readdir(d)) != NULL)
  {
    if (strncmp(ent->d_name, "video", 5))
      continue; // ignore anything not starting with "video"
    string dev_name = string("/dev/") + string(ent->d_name);
    printf("enumerating %s ...\n", dev_name.c_str());
    if ((fd = open(dev_name.c_str(), O_RDWR)) == -1)
      throw std::runtime_error("couldn't open " + dev_name + "  perhaps the " +
                               "permissions are not set correctly?");
    if ((ret = ioctl(fd, VIDIOC_QUERYCAP, &v4l2_cap)) < 0)
      throw std::runtime_error("couldn't query " + dev_name);
    printf("name = [%s]\n", v4l2_cap.card);
    printf("driver = [%s]\n", v4l2_cap.driver);
    printf("location = [%s]\n", v4l2_cap.bus_info);
    close(fd);
    string v4l_dev_path = v4l_path + string("/") + string(ent->d_name) +
                          string("/device");
    // my kernel is using /sys/class/video4linux/videoN/device/inputX/id
    DIR *d2 = opendir(v4l_dev_path.c_str());
    if (!d2)
      throw std::runtime_error("couldn't open " + v4l_dev_path);
    string input_dir;
    while ((ent2 = readdir(d2)) != NULL)
    {
      if (strncmp(ent2->d_name, "input", 5))
        continue; // ignore anything not beginning with "input"

      DIR *input = opendir((v4l_dev_path + string("/") + string(ent2->d_name)).c_str());
      bool output_set = false;
      while ((ent3 = readdir(input)) != NULL)
      {
        if (!strncmp(ent3->d_name, "input", 5))
        {
          input_dir = (string("input/") + string(ent3->d_name )).c_str();
          output_set = true;
          break;
        }
      }
      if (!output_set)
        input_dir = ent2->d_name;
      break;
    }
    closedir(d2);
    if (!input_dir.length())
      throw std::runtime_error("couldn't find input dir in " + v4l_dev_path);
    string vid_fname = v4l_dev_path + string("/") + input_dir +
                       string("/id/vendor");
    string pid_fname = v4l_dev_path + string("/") + input_dir +
                       string("/id/product");
    string ver_fname = v4l_dev_path + string("/") + input_dir +
                       string("/id/version");
    char vid[5], pid[5], ver[5];
    FILE *vid_fp = fopen(vid_fname.c_str(), "r");
    if (!vid_fp)
      throw std::runtime_error("couldn't open " + vid_fname);
    if (!fgets(vid, sizeof(vid), vid_fp))
      throw std::runtime_error("couldn't read VID from " + vid_fname);
    fclose(vid_fp);
    vid[4] = 0;
    printf("vid = [%s]\n", vid);
    FILE *pid_fp = fopen(pid_fname.c_str(), "r");
    if (!pid_fp)
      throw std::runtime_error("couldn't open " + pid_fname);
    if (!fgets(pid, sizeof(pid), pid_fp))
      throw std::runtime_error("couldn't read PID from " + pid_fname);
    fclose(pid_fp);
    printf("pid = [%s]\n", pid);
    FILE *ver_fp = fopen(ver_fname.c_str(), "r");
    if (!ver_fp)
      throw std::runtime_error("couldn't open " + ver_fname);
    if (!fgets(ver, sizeof(ver), ver_fp))
      throw std::runtime_error("couldn't read version from " + ver_fname);
    fclose(ver_fp);
    printf("ver = [%s]\n", ver);
  }
  closedir(d);
}

// saturate input into [0, 255]
inline unsigned char sat(float f)
{
  return (unsigned char)( f >= 255 ? 255 : (f < 0 ? 0 : f));
}

int Cam::grab(unsigned char **frame, uint32_t &bytes_used)
{
  *frame = NULL;
  int ret = 0;
  fd_set rdset;
  timeval timeout;
  FD_ZERO(&rdset);
  FD_SET(fd, &rdset);
  timeout.tv_sec = 1;
  timeout.tv_usec = 0;
  bytes_used = 0;
  ret = select(fd + 1, &rdset, NULL, NULL, &timeout);
  if (ret == 0)
  {
    printf("select timeout in grab\n");
    return -1;
  }
  else if (ret < 0)
  {
    perror("couldn't grab image");
    return -1;
  }
  if (!FD_ISSET(fd, &rdset))
    return -1;
  memset(&buf, 0, sizeof(buf));
  buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  buf.memory = V4L2_MEMORY_MMAP;
  if (ioctl(fd, VIDIOC_DQBUF, &buf) < 0)
    throw std::runtime_error("couldn't dequeue buffer");
  bytes_used = buf.bytesused;
  if (mode == MODE_RGB)
  {
    int num_pixels_different = 0; // just look at the Y channel
    unsigned char *pyuv = (unsigned char *)mem[buf.index];
    // yuyv is 2 bytes per pixel. step through every pixel pair.
    unsigned char *prgb = rgb_frame;
    unsigned char *pyuv_last = last_yuv_frame;
    for (unsigned i = 0; i < width * height * 2; i += 4)
    {
      *prgb++ = sat(pyuv[i]+1.402f  *(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i]-0.34414f*(pyuv[i+1]-128)-0.71414f*(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i]+1.772f  *(pyuv[i+1]-128));
      *prgb++ = sat(pyuv[i+2]+1.402f*(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i+2]-0.34414f*(pyuv[i+1]-128)-0.71414f*(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i+2]+1.772f*(pyuv[i+1]-128));
      if ((int)pyuv[i] - (int)pyuv_last[i] > motion_threshold_luminance ||
          (int)pyuv_last[i] - (int)pyuv[i] > motion_threshold_luminance)
        num_pixels_different++;
      if ((int)pyuv[i+2] - (int)pyuv_last[i+2] > motion_threshold_luminance ||
          (int)pyuv_last[i+2] - (int)pyuv[i+2] > motion_threshold_luminance)
        num_pixels_different++;

      // this gives bgr images...
      /*
      *prgb++ = sat(pyuv[i]+1.772f  *(pyuv[i+1]-128));
      *prgb++ = sat(pyuv[i]-0.34414f*(pyuv[i+1]-128)-0.71414f*(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i]+1.402f  *(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i+2]+1.772f*(pyuv[i+1]-128));
      *prgb++ = sat(pyuv[i+2]-0.34414f*(pyuv[i+1]-128)-0.71414f*(pyuv[i+3]-128));
      *prgb++ = sat(pyuv[i+2]+1.402f*(pyuv[i+3]-128));
      */
    }
    memcpy(last_yuv_frame, pyuv, width * height * 2);
    if (num_pixels_different > motion_threshold_count) // default: always true
      *frame = rgb_frame;
    else
    {
      *frame = NULL; // not enough luminance change
      release(buf.index); // let go of this image
    }
  }
  else if (mode == MODE_YUYV)
  {
    *frame = (uint8_t *)mem[buf.index];
  }
  else // mode == MODE_JPEG
  {
    //if (bytes_used > 100)

      mjpeg2rgb((char*)mem[buf.index], bytes_used, (char*)jpegBuf, width*height);
        *frame = jpegBuf;
  }
  return buf.index;
}

void Cam::release(unsigned buf_idx)
{
  if (buf_idx < NUM_BUFFER)
    if (ioctl(fd, VIDIOC_QBUF, &buf) < 0)
      throw std::runtime_error("couldn't requeue buffer");
}

void Cam::set_control(uint32_t id, int val)
{
  v4l2_control c;
  c.id = id;

  if (ioctl(fd, VIDIOC_G_CTRL, &c) == 0)
  {
    printf("current value of %d is %d\n", id, c.value);
    /*
    perror("unable to get control");
    throw std::runtime_error("unable to get control");
    */
  }
  c.value = val;
  if (ioctl(fd, VIDIOC_S_CTRL, &c) < 0)
  {
    perror("unable to set control");
    throw std::runtime_error("unable to set control");
  }
}

void Cam::set_motion_thresholds(int lum, int count)
{
  motion_threshold_luminance = lum;
  motion_threshold_count = count;
}

void Cam::mjpeg2rgb(char *MJPEG, int len, char *RGB, int NumPixels)
{
  int got_picture;

  memset(RGB, 0, avframe_rgb_size);

#if LIBAVCODEC_VERSION_MAJOR > 52
  int decoded_len;
  AVPacket avpkt;
  av_init_packet(&avpkt);
  
  avpkt.size = len;
  avpkt.data = (unsigned char*)MJPEG;
  decoded_len = avcodec_decode_video2(avcodec_context, avframe_camera, &got_picture, &avpkt);

  if (decoded_len < 0) {
      fprintf(stderr, "Error while decoding frame.\n");
      return;
  }
#else
  avcodec_decode_video(avcodec_context, avframe_camera, &got_picture, (uint8_t *) MJPEG, len);
#endif

  if (!got_picture) {
    fprintf(stderr,"Webcam: expected picture but didn't get it...\n");
    return;
  }

  int xsize = avcodec_context->width;
  int ysize = avcodec_context->height;
  int pic_size = avpicture_get_size(avcodec_context->pix_fmt, xsize, ysize);
  if (pic_size != avframe_camera_size) {
    fprintf(stderr,"outbuf size mismatch.  pic_size: %d bufsize: %d\n",pic_size,avframe_camera_size);
    return;
  }

  video_sws = sws_getContext( xsize, ysize, avcodec_context->pix_fmt, xsize, ysize, PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL);
  sws_scale(video_sws, avframe_camera->data, avframe_camera->linesize, 0, ysize, avframe_rgb->data, avframe_rgb->linesize );
  sws_freeContext(video_sws);  

  int size = avpicture_layout((AVPicture *) avframe_rgb, PIX_FMT_RGB24, xsize, ysize, (uint8_t *)RGB, avframe_rgb_size);
  if (size != avframe_rgb_size) {
    fprintf(stderr,"webcam: avpicture_layout error: %d\n",size);
    return;
  }
}

int Cam::init_mjpeg_decoder(int image_width, int image_height)
{
  avcodec_init();
  avcodec_register_all();

  avcodec = avcodec_find_decoder(CODEC_ID_MJPEG);
  if (!avcodec)
  {
    fprintf(stderr,"Could not find MJPEG decoder\n");
    return 0;
  }

  avcodec_context = avcodec_alloc_context();
  avframe_camera = avcodec_alloc_frame();
  avframe_rgb = avcodec_alloc_frame();

  avpicture_alloc((AVPicture *)avframe_rgb, PIX_FMT_RGB24, image_width, image_height);

  avcodec_context->codec_id = CODEC_ID_MJPEG;
  avcodec_context->width = image_width;
  avcodec_context->height = image_height;

#if LIBAVCODEC_VERSION_MAJOR > 52
  avcodec_context->pix_fmt = PIX_FMT_YUV422P;
  avcodec_context->codec_type = AVMEDIA_TYPE_VIDEO;
#endif

  avframe_camera_size = avpicture_get_size(PIX_FMT_YUV422P, image_width, image_height);
  avframe_rgb_size = avpicture_get_size(PIX_FMT_RGB24, image_width, image_height);

  /* open it */
  if (avcodec_open(avcodec_context, avcodec) < 0)
  {
    fprintf(stderr,"Could not open MJPEG Decoder\n");
    return 0;
  }
  return 1;
}