gstreamer/sys/v4l2/gstv4l2src.c

/* GStreamer
 *
 * gstv4l2src.c: BT8x8/V4L2 source element
 *
 * Copyright (C) 2001-2002 Ronald Bultje <rbultje@ronald.bitfreak.net>
 * Copyright (C) 2006 Edgard Lima <edgard.lima@indt.org.br>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/**
 * SECTION:element-v4l2srcsrc
 *
 * <refsect2>
 * v4l2src can be used to capture video from v4l2 devices, like webcams and tv cards.
 * <title>Example launch line</title>
 * <para>
 * <programlisting>
 * gst-launch v4l2src ! xvimagesink
 * </programlisting>
 * This pipeline shows the video captured from /dev/video0 tv card.
 * </para>
 * <para>
 * <programlisting>
 * gst-launch v4l2src use-fixed-fps=true ! xvimagesink
 * </programlisting>
 * This exemple should be used to capture from web-cams
 * </para>
 * </refsect2>
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>
#include <sys/time.h>
#include "v4l2src_calls.h"
#include <unistd.h>

#include "gstv4l2colorbalance.h"
#include "gstv4l2tuner.h"
#include "gstv4l2xoverlay.h"

static const GstElementDetails gst_v4l2src_details =
GST_ELEMENT_DETAILS ("Video (video4linux2/raw) Source",
    "Source/Video",
    "Reads raw frames from a video4linux2 (BT8x8) device",
    "Ronald Bultje <rbultje@ronald.bitfreak.net>,"
    " Edgard Lima <edgard.lima@indt.org.br>");


GST_DEBUG_CATEGORY (v4l2src_debug);
#define GST_CAT_DEFAULT v4l2src_debug


enum
{
  PROP_0,
  V4L2_STD_OBJECT_PROPS,
  PROP_USE_FIXED_FPS
};

static const guint32 gst_v4l2_formats[] = {
  /* from Linux 2.6.15 videodev2.h */
  V4L2_PIX_FMT_RGB332,
  V4L2_PIX_FMT_RGB555,
  V4L2_PIX_FMT_RGB565,
  V4L2_PIX_FMT_RGB555X,
  V4L2_PIX_FMT_RGB565X,
  V4L2_PIX_FMT_BGR24,
  V4L2_PIX_FMT_RGB24,
  V4L2_PIX_FMT_BGR32,
  V4L2_PIX_FMT_RGB32,
  V4L2_PIX_FMT_GREY,
  V4L2_PIX_FMT_YVU410,
  V4L2_PIX_FMT_YVU420,
  V4L2_PIX_FMT_YUYV,
  V4L2_PIX_FMT_UYVY,
  V4L2_PIX_FMT_YUV422P,
  V4L2_PIX_FMT_YUV411P,
  V4L2_PIX_FMT_Y41P,

  /* two planes -- one Y, one Cr + Cb interleaved  */
  V4L2_PIX_FMT_NV12,
  V4L2_PIX_FMT_NV21,

  /*  The following formats are not defined in the V4L2 specification */
  V4L2_PIX_FMT_YUV410,
  V4L2_PIX_FMT_YUV420,
  V4L2_PIX_FMT_YYUV,
  V4L2_PIX_FMT_HI240,

  /* see http://www.siliconimaging.com/RGB%20Bayer.htm */
#ifdef V4L2_PIX_FMT_SBGGR8
  V4L2_PIX_FMT_SBGGR8,
#endif

  /* compressed formats */
  V4L2_PIX_FMT_MJPEG,
  V4L2_PIX_FMT_JPEG,
  V4L2_PIX_FMT_DV,
  V4L2_PIX_FMT_MPEG,

  /*  Vendor-specific formats   */
  V4L2_PIX_FMT_WNVA,

#ifdef V4L2_PIX_FMT_SN9C10X
  V4L2_PIX_FMT_SN9C10X,
#endif
#ifdef V4L2_PIX_FMT_PWC1
  V4L2_PIX_FMT_PWC1,
#endif
#ifdef V4L2_PIX_FMT_PWC2
  V4L2_PIX_FMT_PWC2,
#endif
};


#define GST_V4L2_FORMAT_COUNT (G_N_ELEMENTS (gst_v4l2_formats))

GST_IMPLEMENT_V4L2_PROBE_METHODS (GstV4l2SrcClass, gst_v4l2src);
GST_IMPLEMENT_V4L2_COLOR_BALANCE_METHODS (GstV4l2Src, gst_v4l2src);
GST_IMPLEMENT_V4L2_TUNER_METHODS (GstV4l2Src, gst_v4l2src);
#ifdef HAVE_XVIDEO
GST_IMPLEMENT_V4L2_XOVERLAY_METHODS (GstV4l2Src, gst_v4l2src);
#endif

static gboolean
gst_v4l2src_iface_supported (GstImplementsInterface * iface, GType iface_type)
{
  GstV4l2Object *v4l2object = GST_V4L2SRC (iface)->v4l2object;

#ifdef HAVE_XVIDEO
  g_assert (iface_type == GST_TYPE_TUNER ||
      iface_type == GST_TYPE_X_OVERLAY || iface_type == GST_TYPE_COLOR_BALANCE);
#else
  g_assert (iface_type == GST_TYPE_TUNER ||
      iface_type == GST_TYPE_COLOR_BALANCE);
#endif

  if (v4l2object->video_fd == -1)
    return FALSE;

#ifdef HAVE_XVIDEO
  if (iface_type == GST_TYPE_X_OVERLAY && !GST_V4L2_IS_OVERLAY (v4l2object))
    return FALSE;
#endif

  return TRUE;
}

static void
gst_v4l2src_interface_init (GstImplementsInterfaceClass * klass)
{
  /*
   * default virtual functions 
   */
  klass->supported = gst_v4l2src_iface_supported;
}

void
gst_v4l2src_init_interfaces (GType type)
{
  static const GInterfaceInfo v4l2iface_info = {
    (GInterfaceInitFunc) gst_v4l2src_interface_init,
    NULL,
    NULL,
  };
  static const GInterfaceInfo v4l2_tuner_info = {
    (GInterfaceInitFunc) gst_v4l2src_tuner_interface_init,
    NULL,
    NULL,
  };
#ifdef HAVE_XVIDEO
  static const GInterfaceInfo v4l2_xoverlay_info = {
    (GInterfaceInitFunc) gst_v4l2src_xoverlay_interface_init,
    NULL,
    NULL,
  };
#endif
  static const GInterfaceInfo v4l2_colorbalance_info = {
    (GInterfaceInitFunc) gst_v4l2src_color_balance_interface_init,
    NULL,
    NULL,
  };
  static const GInterfaceInfo v4l2_propertyprobe_info = {
    (GInterfaceInitFunc) gst_v4l2src_property_probe_interface_init,
    NULL,
    NULL,
  };

  g_type_add_interface_static (type,
      GST_TYPE_IMPLEMENTS_INTERFACE, &v4l2iface_info);
  g_type_add_interface_static (type, GST_TYPE_TUNER, &v4l2_tuner_info);
#ifdef HAVE_XVIDEO
  g_type_add_interface_static (type, GST_TYPE_X_OVERLAY, &v4l2_xoverlay_info);
#endif
  g_type_add_interface_static (type,
      GST_TYPE_COLOR_BALANCE, &v4l2_colorbalance_info);
  g_type_add_interface_static (type, GST_TYPE_PROPERTY_PROBE,
      &v4l2_propertyprobe_info);
}

GST_BOILERPLATE_FULL (GstV4l2Src, gst_v4l2src, GstPushSrc, GST_TYPE_PUSH_SRC,
    gst_v4l2src_init_interfaces);

static void gst_v4l2src_dispose (GObject * object);

/* basesrc methods */
static gboolean gst_v4l2src_start (GstBaseSrc * src);
static gboolean gst_v4l2src_stop (GstBaseSrc * src);
static gboolean gst_v4l2src_set_caps (GstBaseSrc * src, GstCaps * caps);
static GstCaps *gst_v4l2src_get_caps (GstBaseSrc * src);
static GstFlowReturn gst_v4l2src_create (GstPushSrc * src, GstBuffer ** out);

static void gst_v4l2src_fixate (GstPad * pad, GstCaps * caps);

static void gst_v4l2src_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec);
static void gst_v4l2src_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec);

static GstCaps *gst_v4l2src_get_all_caps (void);

static void
gst_v4l2src_base_init (gpointer g_class)
{
  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (g_class);
  GstV4l2SrcClass *gstv4l2src_class = GST_V4L2SRC_CLASS (g_class);

  gstv4l2src_class->v4l2_class_devices = NULL;

  GST_DEBUG_CATEGORY_INIT (v4l2src_debug, "v4l2src", 0, "V4L2 source element");

  gst_element_class_set_details (gstelement_class, &gst_v4l2src_details);

  gst_element_class_add_pad_template
      (gstelement_class,
      gst_pad_template_new ("src", GST_PAD_SRC, GST_PAD_ALWAYS,
          gst_v4l2src_get_all_caps ()));
}

static void
gst_v4l2src_class_init (GstV4l2SrcClass * klass)
{
  GObjectClass *gobject_class;
  GstBaseSrcClass *basesrc_class;
  GstPushSrcClass *pushsrc_class;

  gobject_class = G_OBJECT_CLASS (klass);
  basesrc_class = GST_BASE_SRC_CLASS (klass);
  pushsrc_class = GST_PUSH_SRC_CLASS (klass);

  gobject_class->set_property = gst_v4l2src_set_property;
  gobject_class->get_property = gst_v4l2src_get_property;

  gst_v4l2_object_install_properties_helper (gobject_class);

  g_object_class_install_property
      (gobject_class, PROP_USE_FIXED_FPS,
      g_param_spec_boolean ("use_fixed_fps", "Use Fixed FPS",
          "Drop/Insert frames to reach a certain FPS (TRUE) "
          "or adapt FPS to suit the number of frabbed frames",
          TRUE, G_PARAM_READWRITE));

  basesrc_class->get_caps = gst_v4l2src_get_caps;
  basesrc_class->set_caps = gst_v4l2src_set_caps;
  basesrc_class->start = gst_v4l2src_start;
  basesrc_class->stop = gst_v4l2src_stop;

  pushsrc_class->create = gst_v4l2src_create;

  gobject_class->dispose = gst_v4l2src_dispose;

}

static void
gst_v4l2src_init (GstV4l2Src * v4l2src, GstV4l2SrcClass * klass)
{

  v4l2src->v4l2object = gst_v4l2_object_new (GST_ELEMENT (v4l2src),
      gst_v4l2_get_input, gst_v4l2_set_input, gst_v4l2src_update_fps);

  v4l2src->breq.count = 0;

  v4l2src->formats = NULL;

  /* fps */
  v4l2src->fps_n = 0;
  v4l2src->fps_d = 1;
  v4l2src->use_fixed_fps = TRUE;

  v4l2src->is_capturing = FALSE;

  gst_pad_set_fixatecaps_function (GST_BASE_SRC_PAD (v4l2src),
      gst_v4l2src_fixate);

  gst_base_src_set_live (GST_BASE_SRC (v4l2src), TRUE);
}


static void
gst_v4l2src_dispose (GObject * object)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (object);

  if (v4l2src->formats) {
    gst_v4l2src_clear_format_list (v4l2src);
  }

  if (((GObjectClass *) parent_class)->dispose)
    ((GObjectClass *) parent_class)->dispose (object);
}


static void
gst_v4l2src_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec)
{
  GstV4l2Src *v4l2src;

  g_return_if_fail (GST_IS_V4L2SRC (object));
  v4l2src = GST_V4L2SRC (object);


  if (!gst_v4l2_object_set_property_helper (v4l2src->v4l2object,
          prop_id, value, pspec)) {

    switch (prop_id) {
      case PROP_USE_FIXED_FPS:
        if (!GST_V4L2_IS_ACTIVE (v4l2src->v4l2object)) {
          v4l2src->use_fixed_fps = g_value_get_boolean (value);
        }
        break;

      default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }

  }

}


static void
gst_v4l2src_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec)
{
  GstV4l2Src *v4l2src;

  g_return_if_fail (GST_IS_V4L2SRC (object));
  v4l2src = GST_V4L2SRC (object);

  if (!gst_v4l2_object_get_property_helper (v4l2src->v4l2object,
          prop_id, value, pspec)) {

    switch (prop_id) {
      case PROP_USE_FIXED_FPS:
        g_value_set_boolean (value, v4l2src->use_fixed_fps);
        break;

      default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
  }

}


/* this function is a bit of a last resort */
static void
gst_v4l2src_fixate (GstPad * pad, GstCaps * caps)
{
  GstStructure *structure;
  gint i;
  G_GNUC_UNUSED gchar *caps_str;

  caps_str = gst_caps_to_string (caps);
  GST_DEBUG_OBJECT (GST_PAD_PARENT (pad), "fixating caps %s", caps_str);
  g_free (caps_str);

  for (i = 0; i < gst_caps_get_size (caps); ++i) {
    structure = gst_caps_get_structure (caps, i);
    const GValue *v;

    gst_structure_fixate_field_nearest_int (structure, "width", G_MAXINT);
    gst_structure_fixate_field_nearest_int (structure, "height", G_MAXINT);
    gst_structure_fixate_field_nearest_fraction (structure, "framerate", 15, 2);

    v = gst_structure_get_value (structure, "format");
    if (v && G_VALUE_TYPE (v) != GST_TYPE_FOURCC) {
      guint32 fourcc;

      g_return_if_fail (G_VALUE_TYPE (v) == GST_TYPE_LIST);

      fourcc = gst_value_get_fourcc (gst_value_list_get_value (v, 0));
      gst_structure_set (structure, "format", GST_TYPE_FOURCC, fourcc, NULL);
    }
  }
}

static GstStructure *
gst_v4l2src_v4l2fourcc_to_caps (guint32 fourcc)
{
  GstStructure *structure = NULL;

  switch (fourcc) {
    case V4L2_PIX_FMT_MJPEG:   /* Motion-JPEG */
    case V4L2_PIX_FMT_JPEG:    /* JFIF JPEG */
      structure = gst_structure_new ("image/jpeg", NULL);
      break;
    case V4L2_PIX_FMT_RGB332:
    case V4L2_PIX_FMT_RGB555:
    case V4L2_PIX_FMT_RGB555X:
    case V4L2_PIX_FMT_RGB565:
    case V4L2_PIX_FMT_RGB565X:
    case V4L2_PIX_FMT_RGB24:
    case V4L2_PIX_FMT_BGR24:
    case V4L2_PIX_FMT_RGB32:
    case V4L2_PIX_FMT_BGR32:{
      guint depth = 0, bpp = 0;
      gint endianness = 0;
      guint32 r_mask = 0, b_mask = 0, g_mask = 0;

      switch (fourcc) {
        case V4L2_PIX_FMT_RGB332:
          bpp = depth = 8;
          endianness = G_BYTE_ORDER;    /* 'like, whatever' */
          r_mask = 0xe0;
          g_mask = 0x1c;
          b_mask = 0x03;
          break;
        case V4L2_PIX_FMT_RGB555:
        case V4L2_PIX_FMT_RGB555X:
          bpp = 16;
          depth = 15;
          endianness =
              fourcc == V4L2_PIX_FMT_RGB555X ? G_BIG_ENDIAN : G_LITTLE_ENDIAN;
          r_mask = 0x7c00;
          g_mask = 0x03e0;
          b_mask = 0x001f;
          break;
        case V4L2_PIX_FMT_RGB565:
        case V4L2_PIX_FMT_RGB565X:
          bpp = depth = 16;
          endianness =
              fourcc == V4L2_PIX_FMT_RGB565X ? G_BIG_ENDIAN : G_LITTLE_ENDIAN;
          r_mask = 0xf800;
          g_mask = 0x07e0;
          b_mask = 0x001f;
          break;
        case V4L2_PIX_FMT_RGB24:
          bpp = depth = 24;
          endianness = G_BIG_ENDIAN;
          r_mask = 0xff0000;
          g_mask = 0x00ff00;
          b_mask = 0x0000ff;
          break;
        case V4L2_PIX_FMT_BGR24:
          bpp = depth = 24;
          endianness = G_BIG_ENDIAN;
          r_mask = 0x0000ff;
          g_mask = 0x00ff00;
          b_mask = 0xff0000;
          break;
        case V4L2_PIX_FMT_RGB32:
          bpp = depth = 32;
          endianness = G_BIG_ENDIAN;
          r_mask = 0xff000000;
          g_mask = 0x00ff0000;
          b_mask = 0x0000ff00;
          break;
        case V4L2_PIX_FMT_BGR32:
          bpp = depth = 32;
          endianness = G_BIG_ENDIAN;
          r_mask = 0x000000ff;
          g_mask = 0x0000ff00;
          b_mask = 0x00ff0000;
          break;
        default:
          g_assert_not_reached ();
          break;
      }
      structure = gst_structure_new ("video/x-raw-rgb",
          "bpp", G_TYPE_INT, bpp,
          "depth", G_TYPE_INT, depth,
          "red_mask", G_TYPE_INT, r_mask,
          "green_mask", G_TYPE_INT, g_mask,
          "blue_mask", G_TYPE_INT, b_mask,
          "endianness", G_TYPE_INT, endianness, NULL);
      break;
    }
    case V4L2_PIX_FMT_GREY:    /*  8  Greyscale     */
    case V4L2_PIX_FMT_NV12:    /* 12  Y/CbCr 4:2:0  */
    case V4L2_PIX_FMT_NV21:    /* 12  Y/CrCb 4:2:0  */
    case V4L2_PIX_FMT_YYUV:    /* 16  YUV 4:2:2     */
    case V4L2_PIX_FMT_HI240:   /*  8  8-bit color   */
      /* FIXME: get correct fourccs here */
      break;
    case V4L2_PIX_FMT_YVU410:
    case V4L2_PIX_FMT_YUV410:
    case V4L2_PIX_FMT_YUV420:  /* I420/IYUV */
    case V4L2_PIX_FMT_YUYV:
    case V4L2_PIX_FMT_YVU420:
    case V4L2_PIX_FMT_UYVY:
    case V4L2_PIX_FMT_Y41P:
    case V4L2_PIX_FMT_YUV422P:
    case V4L2_PIX_FMT_YUV411P:{
      guint32 fcc = 0;

      switch (fourcc) {
        case V4L2_PIX_FMT_YVU410:
          fcc = GST_MAKE_FOURCC ('Y', 'V', 'U', '9');
          break;
        case V4L2_PIX_FMT_YUV410:
          fcc = GST_MAKE_FOURCC ('Y', 'U', 'V', '9');
          break;
        case V4L2_PIX_FMT_YUV420:
          fcc = GST_MAKE_FOURCC ('I', '4', '2', '0');
          break;
        case V4L2_PIX_FMT_YUYV:
          fcc = GST_MAKE_FOURCC ('Y', 'U', 'Y', '2');
          break;
        case V4L2_PIX_FMT_YVU420:
          fcc = GST_MAKE_FOURCC ('Y', 'V', '1', '2');
          break;
        case V4L2_PIX_FMT_UYVY:
          fcc = GST_MAKE_FOURCC ('U', 'Y', 'V', 'Y');
          break;
        case V4L2_PIX_FMT_Y41P:
          fcc = GST_MAKE_FOURCC ('Y', '4', '1', 'P');
          break;
        case V4L2_PIX_FMT_YUV411P:
          fcc = GST_MAKE_FOURCC ('Y', '4', '1', 'B');
          break;
        case V4L2_PIX_FMT_YUV422P:
          fcc = GST_MAKE_FOURCC ('Y', '4', '2', 'B');
          break;
        default:
          g_assert_not_reached ();
          break;
      }
      structure = gst_structure_new ("video/x-raw-yuv",
          "format", GST_TYPE_FOURCC, fcc, NULL);
      break;
    }
    case V4L2_PIX_FMT_DV:
      structure =
          gst_structure_new ("video/x-dv", "systemstream", G_TYPE_BOOLEAN, TRUE,
          NULL);
      break;
    case V4L2_PIX_FMT_MPEG:    /* MPEG          */
      /* someone figure out the MPEG format used... */
      break;
    case V4L2_PIX_FMT_WNVA:    /* Winnov hw compres */
      break;
    default:
      GST_DEBUG ("Unknown fourcc 0x%08x %" GST_FOURCC_FORMAT,
          fourcc, GST_FOURCC_ARGS (fourcc));
      break;
  }

  return structure;
}

static guint32
gst_v4l2_fourcc_from_structure (GstStructure * structure)
{
  guint32 fourcc = 0;
  const gchar *mimetype = gst_structure_get_name (structure);

  if (!strcmp (mimetype, "video/x-raw-yuv")) {
    gst_structure_get_fourcc (structure, "format", &fourcc);

    switch (fourcc) {
      case GST_MAKE_FOURCC ('I', '4', '2', '0'):
      case GST_MAKE_FOURCC ('I', 'Y', 'U', 'V'):
        fourcc = V4L2_PIX_FMT_YUV420;
        break;
      case GST_MAKE_FOURCC ('Y', 'U', 'Y', '2'):
        fourcc = V4L2_PIX_FMT_YUYV;
        break;
      case GST_MAKE_FOURCC ('Y', '4', '1', 'P'):
        fourcc = V4L2_PIX_FMT_Y41P;
        break;
      case GST_MAKE_FOURCC ('U', 'Y', 'V', 'Y'):
        fourcc = V4L2_PIX_FMT_UYVY;
        break;
      case GST_MAKE_FOURCC ('Y', 'V', '1', '2'):
        fourcc = V4L2_PIX_FMT_YVU420;
        break;
      case GST_MAKE_FOURCC ('Y', '4', '1', 'B'):
        fourcc = V4L2_PIX_FMT_YUV411P;
        break;
      case GST_MAKE_FOURCC ('Y', '4', '2', 'B'):
        fourcc = V4L2_PIX_FMT_YUV422P;
        break;
    }
  } else if (!strcmp (mimetype, "video/x-raw-rgb")) {
    gint depth, endianness, r_mask;

    gst_structure_get_int (structure, "depth", &depth);
    gst_structure_get_int (structure, "endianness", &endianness);
    gst_structure_get_int (structure, "red_mask", &r_mask);

    switch (depth) {
      case 8:
        fourcc = V4L2_PIX_FMT_RGB332;
        break;
      case 15:
        fourcc = (endianness == G_LITTLE_ENDIAN) ?
            V4L2_PIX_FMT_RGB555 : V4L2_PIX_FMT_RGB555X;
        break;
      case 16:
        fourcc = (endianness == G_LITTLE_ENDIAN) ?
            V4L2_PIX_FMT_RGB565 : V4L2_PIX_FMT_RGB565X;
        break;
      case 24:
        fourcc = (r_mask == 0xFF) ? V4L2_PIX_FMT_BGR24 : V4L2_PIX_FMT_RGB24;
        break;
      case 32:
        fourcc = (r_mask == 0xFF) ? V4L2_PIX_FMT_BGR32 : V4L2_PIX_FMT_RGB32;
        break;
    }
  } else if (strcmp (mimetype, "video/x-dv") == 0) {
    fourcc = V4L2_PIX_FMT_DV;
  } else if (strcmp (mimetype, "image/jpeg") == 0) {
    fourcc = V4L2_PIX_FMT_JPEG;
  }

  return fourcc;
}

static struct v4l2_fmtdesc *
gst_v4l2src_get_format_from_fourcc (GstV4l2Src * v4l2src, guint32 fourcc)
{
  struct v4l2_fmtdesc *fmt;
  GSList *walk;

  if (fourcc == 0)
    return NULL;

  walk = v4l2src->formats;
  while (walk) {
    fmt = (struct v4l2_fmtdesc *) walk->data;
    if (fmt->pixelformat == fourcc)
      return fmt;
    /* special case for jpeg */
    if ((fmt->pixelformat == V4L2_PIX_FMT_MJPEG && fourcc == V4L2_PIX_FMT_JPEG)
        || (fmt->pixelformat == V4L2_PIX_FMT_JPEG
            && fourcc == V4L2_PIX_FMT_MJPEG)) {
      return fmt;
    }
    walk = g_slist_next (walk);
  }

  return NULL;
}

static struct v4l2_fmtdesc *
gst_v4l2_caps_to_v4l2fourcc (GstV4l2Src * v4l2src, GstStructure * structure)
{
  return gst_v4l2src_get_format_from_fourcc (v4l2src,
      gst_v4l2_fourcc_from_structure (structure));
}

static GstCaps *
gst_v4l2src_get_all_caps (void)
{
  static GstCaps *caps = NULL;

  if (caps == NULL) {
    GstStructure *structure;
    guint i;

    caps = gst_caps_new_empty ();
    for (i = 0; i < GST_V4L2_FORMAT_COUNT; i++) {
      structure = gst_v4l2src_v4l2fourcc_to_caps (gst_v4l2_formats[i]);
      if (structure) {
        gst_structure_set (structure,
            "width", GST_TYPE_INT_RANGE, 1, 4096,
            "height", GST_TYPE_INT_RANGE, 1, 4096,
            "framerate", GST_TYPE_FRACTION_RANGE, 1, 1, 100, 1, NULL);
        gst_caps_append_structure (caps, structure);
      }
    }
  }

  return caps;
}

static GstCaps *
gst_v4l2src_get_caps (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);
  GstCaps *caps;
  struct v4l2_fmtdesc *format;
  int min_w, max_w, min_h, max_h;
  GSList *walk;
  GstStructure *structure;
  guint fps_n, fps_d;

  if (!GST_V4L2_IS_OPEN (v4l2src->v4l2object)) {
    return
        gst_caps_copy (gst_pad_get_pad_template_caps (GST_BASE_SRC_PAD
            (v4l2src)));
  }

  if (!v4l2src->formats)
    gst_v4l2src_fill_format_list (v4l2src);

  /* build our own capslist */
  caps = gst_caps_new_empty ();
  walk = v4l2src->formats;
  if (!gst_v4l2src_get_fps (v4l2src, &fps_n, &fps_d)) {
    GST_DEBUG_OBJECT (v4l2src, "frame rate is unknown.");
    fps_n = 0;
    fps_d = 1;
  }
  while (walk) {
    format = (struct v4l2_fmtdesc *) walk->data;
    walk = g_slist_next (walk);

    /* get size delimiters */
    if (!gst_v4l2src_get_size_limits (v4l2src, format,
            &min_w, &max_w, &min_h, &max_h)) {
      continue;
    }
    /* template */
    min_w = CLAMP (min_w, 1, 4096);
    min_h = CLAMP (min_h, 1, 4096);
    max_w = CLAMP (max_w, min_w, 4096);
    max_h = CLAMP (max_h, min_h, 4096);

    /* add to list */
    structure = gst_v4l2src_v4l2fourcc_to_caps (format->pixelformat);

    if (structure) {
      gst_structure_set (structure,
          "width", GST_TYPE_INT_RANGE, min_w, max_w,
          "height", GST_TYPE_INT_RANGE, min_h, max_h, NULL);
      if (fps_n > 0) {
        gst_structure_set (structure, "framerate", GST_TYPE_FRACTION,
            fps_n, fps_d, NULL);
      } else {
        gst_structure_set (structure, "framerate", GST_TYPE_FRACTION_RANGE,
            1, 1, 100, 1, NULL);
      }

      gst_caps_append_structure (caps, structure);

    }
  }

  return caps;
}

static gboolean
gst_v4l2src_set_caps (GstBaseSrc * src, GstCaps * caps)
{
  GstV4l2Src *v4l2src;
  gint w, h;
  GstStructure *structure;
  struct v4l2_fmtdesc *format;

  v4l2src = GST_V4L2SRC (src);

  /* if we're not open, punt -- we'll get setcaps'd later via negotiate */
  if (!GST_V4L2_IS_OPEN (v4l2src->v4l2object))
    return FALSE;

  /* make sure we stop capturing and dealloc buffers */
  if (GST_V4L2_IS_ACTIVE (v4l2src->v4l2object)) {
    if (!gst_v4l2src_capture_stop (v4l2src))
      return FALSE;
    if (!gst_v4l2src_capture_deinit (v4l2src))
      return FALSE;
  }

  /* it's fixed, one struct */
  structure = gst_caps_get_structure (caps, 0);

  /* we want our own v4l2 type of fourcc codes */
  if (!(format = gst_v4l2_caps_to_v4l2fourcc (v4l2src, structure))) {
    return FALSE;
  }

  gst_structure_get_int (structure, "width", &w);
  gst_structure_get_int (structure, "height", &h);

  GST_DEBUG_OBJECT (v4l2src, "trying to set_capture %dx%d, format %s",
      w, h, format->description);
  /* this only fills in v4l2src->mmap values */
  if (!gst_v4l2src_set_capture (v4l2src, format, w, h)) {
    GST_WARNING_OBJECT (v4l2src, "could not set_capture %dx%d, format %s",
        w, h, format->description);
    return FALSE;
  }

  if (!gst_v4l2src_capture_init (v4l2src))
    return FALSE;

  if (!gst_v4l2src_capture_start (v4l2src))
    return FALSE;

  return TRUE;
}

/* start and stop are not symmetric -- start will open the device, but not start
   capture. it's setcaps that will start capture, which is called via basesrc's
   negotiate method. stop will both stop capture and close the device.
*/
static gboolean
gst_v4l2src_start (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);

  if (!gst_v4l2_object_start (v4l2src->v4l2object))
    return FALSE;

  v4l2src->offset = 0;

  return TRUE;
}

static gboolean
gst_v4l2src_stop (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);

  if (GST_V4L2_IS_ACTIVE (v4l2src->v4l2object)
      && !gst_v4l2src_capture_stop (v4l2src))
    return FALSE;

  if (v4l2src->v4l2object->buffer != NULL) {
    if (!gst_v4l2src_capture_deinit (v4l2src))
      return FALSE;
  }

  if (!gst_v4l2_object_stop (v4l2src->v4l2object))
    return FALSE;

  return TRUE;
}

static GstFlowReturn
gst_v4l2src_get_read (GstV4l2Src * v4l2src, GstBuffer ** buf)
{
  gint amount;
  gint buffersize;

  buffersize = v4l2src->format.fmt.pix.sizeimage;

  do {
    *buf = gst_v4l2src_buffer_new (v4l2src, buffersize, NULL, NULL);
    GST_BUFFER_OFFSET (*buf) = GST_BUFFER_OFFSET_NONE;

    amount =
        read (v4l2src->v4l2object->video_fd, GST_BUFFER_DATA (*buf),
        buffersize);
    if (amount == buffersize) {
      break;
    } else if (amount == -1) {
      if (errno == EAGAIN || errno == EINTR) {
        continue;
      } else {
        GST_ELEMENT_ERROR (v4l2src, RESOURCE, SYNC, (NULL),
            ("error read()ing a buffer on device %s: %s",
                v4l2src->v4l2object->videodev, g_strerror (errno)));
        gst_buffer_unref (*buf);
        return GST_FLOW_ERROR;
      }
    } else {
      GST_ELEMENT_ERROR (v4l2src, RESOURCE, SYNC, (NULL),
          ("error read()ing a buffer on device %s: got only %d bytes instead of expected %d",
              v4l2src->v4l2object->videodev, amount, buffersize));
      gst_buffer_unref (*buf);
      return GST_FLOW_ERROR;
    }
  } while (TRUE);

  return GST_FLOW_OK;

}


static GstFlowReturn
gst_v4l2src_get_mmap (GstV4l2Src * v4l2src, GstBuffer ** buf)
{
  gint i, num = -1;


  /* grab a frame from the device */
  num = gst_v4l2src_grab_frame (v4l2src);
  if (num == -1)
    return GST_FLOW_ERROR;

  i = v4l2src->format.fmt.pix.sizeimage;

  /* check if this is the last buffer in the queue. If so do a memcpy to put it back asap
     to avoid framedrops and deadlocks because of stupid elements */
  if (g_atomic_int_get (&v4l2src->pool->refcount) == v4l2src->breq.count) {
    GST_LOG_OBJECT (v4l2src, "using memcpy'd buffer");
    *buf = gst_v4l2src_buffer_new (v4l2src, i, NULL, NULL);
    memcpy (GST_BUFFER_DATA (*buf), v4l2src->pool->buffers[num].start, i);
    if (!gst_v4l2src_queue_frame (v4l2src, num)) {
      gst_buffer_unref (*buf);
      return GST_FLOW_ERROR;
    }
  } else {
    GST_LOG_OBJECT (v4l2src, "using mmap'd buffer");
    *buf =
        gst_v4l2src_buffer_new (v4l2src, i, v4l2src->pool->buffers[num].start,
        &v4l2src->pool->buffers[num]);
    /* no need to be careful here, both are > 0, because the element uses them */
    g_atomic_int_inc (&v4l2src->pool->buffers[num].refcount);
    g_atomic_int_inc (&v4l2src->pool->refcount);
  }

  return GST_FLOW_OK;
}

static GstFlowReturn
gst_v4l2src_create (GstPushSrc * src, GstBuffer ** buf)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);
  GstFlowReturn ret;

  if (v4l2src->use_fixed_fps && v4l2src->fps_n == 0) {
    GST_ELEMENT_ERROR (v4l2src, RESOURCE, SETTINGS, (NULL),
        ("could not get frame rate for element"));
    return GST_FLOW_ERROR;
  }

  if (v4l2src->breq.memory == V4L2_MEMORY_MMAP) {
    ret = gst_v4l2src_get_mmap (v4l2src, buf);
  } else {
    ret = gst_v4l2src_get_read (v4l2src, buf);
  }

  return ret;
}