gstreamer/sys/winks/gstksvideosrc.c

/*
 * Copyright (C) 2008 Ole André Vadla Ravnås <ole.andre.ravnas@tandberg.com>
 *
 * 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-ksvideosrc
 *
 * Provides low-latency video capture from WDM cameras on Windows.
 *
 * <refsect2>
 * <title>Example pipelines</title>
 * |[
 * gst-launch -v ksvideosrc do-stats=TRUE ! ffmpegcolorspace ! dshowvideosink
 * ]| Capture from a camera and render using dshowvideosink.
 * |[
 * gst-launch -v ksvideosrc do-stats=TRUE ! image/jpeg, width=640, height=480
 * ! jpegdec ! ffmpegcolorspace ! dshowvideosink
 * ]| Capture from an MJPEG camera and render using dshowvideosink.
 * </refsect2>
 */

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

#include "gstksvideosrc.h"

#include "gstksclock.h"
#include "gstksvideodevice.h"
#include "kshelpers.h"
#include "ksvideohelpers.h"

#define ENABLE_CLOCK_DEBUG 0

#define DEFAULT_DEVICE_PATH     NULL
#define DEFAULT_DEVICE_NAME     NULL
#define DEFAULT_DEVICE_INDEX    -1
#define DEFAULT_ENSLAVE_KSCLOCK FALSE
#define DEFAULT_DO_STATS        FALSE
#define DEFAULT_ENABLE_QUIRKS   TRUE

enum
{
  PROP_0,
  PROP_DEVICE_PATH,
  PROP_DEVICE_NAME,
  PROP_DEVICE_INDEX,
  PROP_ENSLAVE_KSCLOCK,
  PROP_DO_STATS,
  PROP_FPS,
  PROP_ENABLE_QUIRKS,
};

GST_DEBUG_CATEGORY (gst_ks_debug);
#define GST_CAT_DEFAULT gst_ks_debug

typedef struct
{
  /* Properties */
  gchar *device_path;
  gchar *device_name;
  gint device_index;
  gboolean enslave_ksclock;
  gboolean do_stats;
  gboolean enable_quirks;

  /* State */
  GstKsClock *ksclock;
  GstKsVideoDevice *device;

  guint64 offset;
  GstClockTime prev_ts;

  /* Statistics */
  GstClockTime last_sampling;
  guint count;
  guint fps;
} GstKsVideoSrcPrivate;

#define GST_KS_VIDEO_SRC_GET_PRIVATE(o) \
    (G_TYPE_INSTANCE_GET_PRIVATE ((o), GST_TYPE_KS_VIDEO_SRC, \
    GstKsVideoSrcPrivate))

static void gst_ks_video_src_finalize (GObject * object);
static void gst_ks_video_src_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec);
static void gst_ks_video_src_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec);

static void gst_ks_video_src_reset (GstKsVideoSrc * self);

static GstStateChangeReturn gst_ks_video_src_change_state (GstElement * element,
    GstStateChange transition);
static gboolean gst_ks_video_src_set_clock (GstElement * element,
    GstClock * clock);

static GstCaps *gst_ks_video_src_get_caps (GstBaseSrc * basesrc);
static gboolean gst_ks_video_src_set_caps (GstBaseSrc * basesrc,
    GstCaps * caps);
static void gst_ks_video_src_fixate (GstBaseSrc * basesrc, GstCaps * caps);
static gboolean gst_ks_video_src_query (GstBaseSrc * basesrc, GstQuery * query);
static gboolean gst_ks_video_src_unlock (GstBaseSrc * basesrc);
static gboolean gst_ks_video_src_unlock_stop (GstBaseSrc * basesrc);

static GstFlowReturn gst_ks_video_src_create (GstPushSrc * pushsrc,
    GstBuffer ** buffer);

GST_BOILERPLATE (GstKsVideoSrc, gst_ks_video_src, GstPushSrc,
    GST_TYPE_PUSH_SRC);

static void
gst_ks_video_src_base_init (gpointer gclass)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (gclass);
  static GstElementDetails element_details = {
    "KsVideoSrc",
    "Source/Video",
    "Stream data from a video capture device through Windows kernel streaming",
    "Ole André Vadla Ravnås <ole.andre.ravnas@tandberg.com>\n"
        "Haakon Sporsheim <hakon.sporsheim@tandberg.com>"
  };

  gst_element_class_set_details (element_class, &element_details);

  gst_element_class_add_pad_template (element_class,
      gst_pad_template_new ("src", GST_PAD_SRC, GST_PAD_ALWAYS,
          ks_video_get_all_caps ()));
}

static void
gst_ks_video_src_class_init (GstKsVideoSrcClass * klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (klass);
  GstBaseSrcClass *gstbasesrc_class = GST_BASE_SRC_CLASS (klass);
  GstPushSrcClass *gstpushsrc_class = GST_PUSH_SRC_CLASS (klass);

  g_type_class_add_private (klass, sizeof (GstKsVideoSrcPrivate));

  gobject_class->finalize = gst_ks_video_src_finalize;
  gobject_class->get_property = gst_ks_video_src_get_property;
  gobject_class->set_property = gst_ks_video_src_set_property;

  gstelement_class->change_state =
      GST_DEBUG_FUNCPTR (gst_ks_video_src_change_state);
  gstelement_class->set_clock = GST_DEBUG_FUNCPTR (gst_ks_video_src_set_clock);

  gstbasesrc_class->get_caps = GST_DEBUG_FUNCPTR (gst_ks_video_src_get_caps);
  gstbasesrc_class->set_caps = GST_DEBUG_FUNCPTR (gst_ks_video_src_set_caps);
  gstbasesrc_class->fixate = GST_DEBUG_FUNCPTR (gst_ks_video_src_fixate);
  gstbasesrc_class->query = GST_DEBUG_FUNCPTR (gst_ks_video_src_query);
  gstbasesrc_class->unlock = GST_DEBUG_FUNCPTR (gst_ks_video_src_unlock);
  gstbasesrc_class->unlock_stop =
      GST_DEBUG_FUNCPTR (gst_ks_video_src_unlock_stop);

  gstpushsrc_class->create = GST_DEBUG_FUNCPTR (gst_ks_video_src_create);

  g_object_class_install_property (gobject_class, PROP_DEVICE_PATH,
      g_param_spec_string ("device-path", "Device Path",
          "The device path", DEFAULT_DEVICE_PATH,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_DEVICE_NAME,
      g_param_spec_string ("device-name", "Device Name",
          "The human-readable device name", DEFAULT_DEVICE_NAME,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_DEVICE_INDEX,
      g_param_spec_int ("device-index", "Device Index",
          "The zero-based device index", -1, G_MAXINT, DEFAULT_DEVICE_INDEX,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_ENSLAVE_KSCLOCK,
      g_param_spec_boolean ("enslave-ksclock", "Enslave the clock used by KS",
          "Enslave the clocked used by Kernel Streaming",
          DEFAULT_ENSLAVE_KSCLOCK, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_DO_STATS,
      g_param_spec_boolean ("do-stats", "Enable statistics",
          "Enable logging of statistics", DEFAULT_DO_STATS,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_FPS,
      g_param_spec_int ("fps", "Frames per second",
          "Last measured framerate, if statistics are enabled",
          -1, G_MAXINT, -1, G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_ENABLE_QUIRKS,
      g_param_spec_boolean ("enable-quirks", "Enable quirks",
          "Enable driver-specific quirks", DEFAULT_ENABLE_QUIRKS,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));

  GST_DEBUG_CATEGORY_INIT (gst_ks_debug, "ksvideosrc",
      0, "Kernel streaming video source");
}

static void
gst_ks_video_src_init (GstKsVideoSrc * self, GstKsVideoSrcClass * gclass)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  GstBaseSrc *basesrc = GST_BASE_SRC (self);

  gst_base_src_set_live (basesrc, TRUE);
  gst_base_src_set_format (basesrc, GST_FORMAT_TIME);

  gst_ks_video_src_reset (self);

  priv->device_path = DEFAULT_DEVICE_PATH;
  priv->device_name = DEFAULT_DEVICE_NAME;
  priv->device_index = DEFAULT_DEVICE_INDEX;
  priv->enslave_ksclock = DEFAULT_ENSLAVE_KSCLOCK;
  priv->do_stats = DEFAULT_DO_STATS;
  priv->enable_quirks = DEFAULT_ENABLE_QUIRKS;
}

static void
gst_ks_video_src_finalize (GObject * object)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (object);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  g_free (priv->device_name);
  g_free (priv->device_path);

  G_OBJECT_CLASS (parent_class)->finalize (object);
}

static void
gst_ks_video_src_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (object);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  switch (prop_id) {
    case PROP_DEVICE_PATH:
      g_value_set_string (value, priv->device_path);
      break;
    case PROP_DEVICE_NAME:
      g_value_set_string (value, priv->device_name);
      break;
    case PROP_DEVICE_INDEX:
      g_value_set_int (value, priv->device_index);
      break;
    case PROP_ENSLAVE_KSCLOCK:
      g_value_set_boolean (value, priv->enslave_ksclock);
      break;
    case PROP_DO_STATS:
      GST_OBJECT_LOCK (object);
      g_value_set_boolean (value, priv->do_stats);
      GST_OBJECT_UNLOCK (object);
      break;
    case PROP_FPS:
      GST_OBJECT_LOCK (object);
      g_value_set_int (value, priv->fps);
      GST_OBJECT_UNLOCK (object);
      break;
    case PROP_ENABLE_QUIRKS:
      g_value_set_boolean (value, priv->enable_quirks);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_ks_video_src_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (object);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  switch (prop_id) {
    case PROP_DEVICE_PATH:
      g_free (priv->device_path);
      priv->device_path = g_value_dup_string (value);
      break;
    case PROP_DEVICE_NAME:
      g_free (priv->device_name);
      priv->device_name = g_value_dup_string (value);
      break;
    case PROP_DEVICE_INDEX:
      priv->device_index = g_value_get_int (value);
      break;
    case PROP_ENSLAVE_KSCLOCK:
      GST_OBJECT_LOCK (object);
      if (priv->device == NULL)
        priv->enslave_ksclock = g_value_get_boolean (value);
      else
        g_warning ("enslave-ksclock may only be changed while in NULL state");
      GST_OBJECT_UNLOCK (object);
      break;
    case PROP_DO_STATS:
      GST_OBJECT_LOCK (object);
      priv->do_stats = g_value_get_boolean (value);
      GST_OBJECT_UNLOCK (object);
      break;
    case PROP_ENABLE_QUIRKS:
      priv->enable_quirks = g_value_get_boolean (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_ks_video_src_reset (GstKsVideoSrc * self)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  /* Reset statistics */
  priv->last_sampling = GST_CLOCK_TIME_NONE;
  priv->count = 0;
  priv->fps = -1;

  /* Reset timestamping state */
  priv->offset = 0;
  priv->prev_ts = GST_CLOCK_TIME_NONE;
}

static void
gst_ks_video_src_apply_driver_quirks (GstKsVideoSrc * self)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  HMODULE mod;

  /*
   * Logitech's driver software injects the following DLL into all processes
   * spawned. This DLL does lots of nasty tricks, sitting in between the
   * application and the low-level ntdll API (NtCreateFile, NtClose,
   * NtDeviceIoControlFile, NtDuplicateObject, etc.), making all sorts
   * of assumptions on which application threads do what.
   *
   * We could later work around this by having a worker-thread open the
   * device, take care of doing set_caps() when asked to, closing the device
   * when shutting down, and so forth.
   *
   * The only regression that this quirk causes is that the video effects
   * feature doesn't work.
   */
  mod = GetModuleHandle ("LVPrcInj.dll");
  if (mod != NULL) {
    GST_DEBUG_OBJECT (self, "hostile Logitech DLL detected, neutralizing it");

    /*
     * We know that no-one's actually keeping this handle around to decrement
     * its reference count, so we'll take care of that job. The DLL's DllMain
     * implementation takes care of rolling back changes when it gets unloaded,
     * so this seems to be the cleanest and most future-proof way that we can
     * get rid of it...
     */
    FreeLibrary (mod);

    /* Paranoia: verify that it's no longer there */
    mod = GetModuleHandle ("LVPrcInj.dll");
    if (mod != NULL)
      GST_WARNING_OBJECT (self, "failed to neutralize hostile Logitech DLL");
  }
}

static gboolean
gst_ks_video_src_open_device (GstKsVideoSrc * self)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  GstKsVideoDevice *device = NULL;
  GList *devices, *cur;

  g_assert (priv->device == NULL);

  devices = ks_enumerate_devices (&KSCATEGORY_VIDEO);
  if (devices == NULL)
    goto error_no_devices;

  for (cur = devices; cur != NULL; cur = cur->next) {
    KsDeviceEntry *entry = cur->data;

    GST_DEBUG_OBJECT (self, "device %d: name='%s' path='%s'",
        entry->index, entry->name, entry->path);
  }

  for (cur = devices; cur != NULL && device == NULL; cur = cur->next) {
    KsDeviceEntry *entry = cur->data;
    gboolean match;

    if (priv->device_path != NULL) {
      match = g_strcasecmp (entry->path, priv->device_path) == 0;
    } else if (priv->device_name != NULL) {
      match = g_strcasecmp (entry->name, priv->device_name) == 0;
    } else if (priv->device_index >= 0) {
      match = entry->index == priv->device_index;
    } else {
      match = TRUE;             /* pick the first entry */
    }

    if (match) {
      priv->ksclock = NULL;

      if (priv->enslave_ksclock) {
        priv->ksclock = g_object_new (GST_TYPE_KS_CLOCK, NULL);
        if (priv->ksclock != NULL && !gst_ks_clock_open (priv->ksclock)) {
          g_object_unref (priv->ksclock);
          priv->ksclock = NULL;
        }

        if (priv->ksclock == NULL)
          GST_WARNING_OBJECT (self, "Failed to create/open KsClock");
      }

      device = g_object_new (GST_TYPE_KS_VIDEO_DEVICE,
          "clock", priv->ksclock, "device-path", entry->path, NULL);
    }

    ks_device_entry_free (entry);
  }

  g_list_free (devices);

  if (device == NULL)
    goto error_no_match;

  if (!gst_ks_video_device_open (device))
    goto error_open;

  priv->device = device;

  return TRUE;

  /* ERRORS */
error_no_devices:
  {
    GST_ELEMENT_ERROR (self, RESOURCE, NOT_FOUND,
        ("No video capture devices found"), (NULL));
    return FALSE;
  }
error_no_match:
  {
    if (priv->device_path != NULL) {
      GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
          ("Specified video capture device with path '%s' not found",
              priv->device_path), (NULL));
    } else if (priv->device_name != NULL) {
      GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
          ("Specified video capture device with name '%s' not found",
              priv->device_name), (NULL));
    } else {
      GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
          ("Specified video capture device with index %d not found",
              priv->device_index), (NULL));
    }
    return FALSE;
  }
error_open:
  {
    GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ,
        ("Failed to open device"), (NULL));
    g_object_unref (device);
    return FALSE;
  }
}

static void
gst_ks_video_src_close_device (GstKsVideoSrc * self)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  g_assert (priv->device != NULL);

  gst_ks_video_device_close (priv->device);
  g_object_unref (priv->device);
  priv->device = NULL;

  if (priv->ksclock != NULL) {
    gst_ks_clock_close (priv->ksclock);
    g_object_unref (priv->ksclock);
    priv->ksclock = NULL;
  }

  gst_ks_video_src_reset (self);
}

static GstStateChangeReturn
gst_ks_video_src_change_state (GstElement * element, GstStateChange transition)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (element);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  GstStateChangeReturn ret;

  switch (transition) {
    case GST_STATE_CHANGE_NULL_TO_READY:
      if (priv->enable_quirks)
        gst_ks_video_src_apply_driver_quirks (self);
      if (!gst_ks_video_src_open_device (self))
        goto open_failed;
      break;
  }

  ret = GST_ELEMENT_CLASS (parent_class)->change_state (element, transition);

  switch (transition) {
    case GST_STATE_CHANGE_READY_TO_NULL:
      gst_ks_video_src_close_device (self);
      break;
  }

  return ret;

  /* ERRORS */
open_failed:
  {
    return GST_STATE_CHANGE_FAILURE;
  }
}

static gboolean
gst_ks_video_src_set_clock (GstElement * element, GstClock * clock)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (element);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  GST_OBJECT_LOCK (element);
  if (priv->ksclock != NULL)
    gst_ks_clock_provide_master_clock (priv->ksclock, clock);
  GST_OBJECT_UNLOCK (element);

  return TRUE;
}

static GstCaps *
gst_ks_video_src_get_caps (GstBaseSrc * basesrc)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (basesrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  if (priv->device != NULL)
    return gst_ks_video_device_get_available_caps (priv->device);
  else
    return NULL;                /* BaseSrc will return template caps */
}

static gboolean
gst_ks_video_src_set_caps (GstBaseSrc * basesrc, GstCaps * caps)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (basesrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  if (priv->device == NULL)
    return FALSE;

  if (!gst_ks_video_device_set_caps (priv->device, caps))
    return FALSE;

  if (!gst_ks_video_device_set_state (priv->device, KSSTATE_RUN))
    return FALSE;

  return TRUE;
}

static void
gst_ks_video_src_fixate (GstBaseSrc * basesrc, GstCaps * caps)
{
  GstStructure *structure = gst_caps_get_structure (caps, 0);

  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",
      G_MAXINT, 1);
}

static gboolean
gst_ks_video_src_query (GstBaseSrc * basesrc, GstQuery * query)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (basesrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  gboolean result = FALSE;

  switch (GST_QUERY_TYPE (query)) {
    case GST_QUERY_LATENCY:{
      GstClockTime min_latency, max_latency;

      if (priv->device == NULL)
        goto beach;

      result = gst_ks_video_device_get_latency (priv->device, &min_latency,
          &max_latency);
      if (!result)
        goto beach;

      GST_DEBUG_OBJECT (self, "reporting latency of min %" GST_TIME_FORMAT
          " max %" GST_TIME_FORMAT,
          GST_TIME_ARGS (min_latency), GST_TIME_ARGS (max_latency));

      gst_query_set_latency (query, TRUE, min_latency, max_latency);
      break;
    }
    default:
      result = GST_BASE_SRC_CLASS (parent_class)->query (basesrc, query);
      break;
  }

beach:
  return result;
}

static gboolean
gst_ks_video_src_unlock (GstBaseSrc * basesrc)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (basesrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  GST_DEBUG_OBJECT (self, "%s", G_STRFUNC);

  gst_ks_video_device_cancel (priv->device);
  return TRUE;
}

static gboolean
gst_ks_video_src_unlock_stop (GstBaseSrc * basesrc)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (basesrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);

  GST_DEBUG_OBJECT (self, "%s", G_STRFUNC);

  gst_ks_video_device_cancel_stop (priv->device);
  return TRUE;
}

static gboolean
gst_ks_video_src_timestamp_buffer (GstKsVideoSrc * self, GstBuffer * buf,
    GstClockTime presentation_time)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  GstClockTime duration;
  GstClock *clock;
  GstClockTime timestamp;

  duration = gst_ks_video_device_get_duration (priv->device);

  GST_OBJECT_LOCK (self);
  clock = GST_ELEMENT_CLOCK (self);
  if (clock != NULL) {
    gst_object_ref (clock);
    timestamp = GST_ELEMENT (self)->base_time;

    if (GST_CLOCK_TIME_IS_VALID (presentation_time)) {
      if (presentation_time > GST_ELEMENT (self)->base_time)
        presentation_time -= GST_ELEMENT (self)->base_time;
      else
        presentation_time = 0;
    }
  } else {
    timestamp = GST_CLOCK_TIME_NONE;
  }
  GST_OBJECT_UNLOCK (self);

  if (clock != NULL) {

    /* The time according to the current clock */
    timestamp = gst_clock_get_time (clock) - timestamp;
    if (timestamp > duration)
      timestamp -= duration;
    else
      timestamp = 0;

    if (GST_CLOCK_TIME_IS_VALID (presentation_time)) {
      GstClockTimeDiff diff = GST_CLOCK_DIFF (timestamp, presentation_time);
      GST_DEBUG_OBJECT (self, "Diff between our and the driver's timestamp: %"
          G_GINT64_FORMAT, diff);
    }

    gst_object_unref (clock);
    clock = NULL;

    /* Unless it's the first frame, align the current timestamp on a multiple
     * of duration since the previous */
    if (GST_CLOCK_TIME_IS_VALID (priv->prev_ts)) {
      GstClockTime delta;
      guint delta_remainder, delta_offset;

      /* REVISIT: I've seen this happen with the GstSystemClock on Windows,
       *          scary... */
      if (timestamp < priv->prev_ts) {
        GST_WARNING_OBJECT (self, "clock is ticking backwards");
        return FALSE;
      }

      /* Round to a duration boundary */
      delta = timestamp - priv->prev_ts;
      delta_remainder = delta % duration;

      if (delta_remainder < duration / 3)
        timestamp -= delta_remainder;
      else
        timestamp += duration - delta_remainder;

      /* How many frames are we off then? */
      delta = timestamp - priv->prev_ts;
      delta_offset = delta / duration;

      if (delta_offset == 1)    /* perfect */
        GST_BUFFER_FLAG_UNSET (buf, GST_BUFFER_FLAG_DISCONT);
      else if (delta_offset > 1) {
        guint lost = delta_offset - 1;
#if ENABLE_CLOCK_DEBUG
        GST_INFO_OBJECT (self, "lost %d frame%s, setting discont flag",
            lost, (lost > 1) ? "s" : "");
#endif
        GST_BUFFER_FLAG_SET (buf, GST_BUFFER_FLAG_DISCONT);
      } else if (delta_offset == 0) {   /* overproduction, skip this frame */
#if ENABLE_CLOCK_DEBUG
        GST_INFO_OBJECT (self, "skipping frame");
#endif
        return FALSE;
      }

      priv->offset += delta_offset;
    }

    priv->prev_ts = timestamp;
  }

  GST_BUFFER_OFFSET (buf) = priv->offset;
  GST_BUFFER_OFFSET_END (buf) = GST_BUFFER_OFFSET (buf) + 1;
  GST_BUFFER_TIMESTAMP (buf) = timestamp;
  GST_BUFFER_DURATION (buf) = duration;

  return TRUE;
}

static void
gst_ks_video_src_update_statistics (GstKsVideoSrc * self)
{
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  GstClock *clock;

  GST_OBJECT_LOCK (self);
  clock = GST_ELEMENT_CLOCK (self);
  if (clock != NULL)
    gst_object_ref (clock);
  GST_OBJECT_UNLOCK (self);

  if (clock != NULL) {
    GstClockTime now = gst_clock_get_time (clock);
    gst_object_unref (clock);

    priv->count++;

    if (GST_CLOCK_TIME_IS_VALID (priv->last_sampling)) {
      if (now - priv->last_sampling >= GST_SECOND) {
        GST_OBJECT_LOCK (self);
        priv->fps = priv->count;
        GST_OBJECT_UNLOCK (self);

        g_object_notify (G_OBJECT (self), "fps");

        priv->last_sampling = now;
        priv->count = 0;
      }
    } else {
      priv->last_sampling = now;
    }
  }
}

static GstFlowReturn
gst_ks_video_src_create (GstPushSrc * pushsrc, GstBuffer ** buffer)
{
  GstKsVideoSrc *self = GST_KS_VIDEO_SRC (pushsrc);
  GstKsVideoSrcPrivate *priv = GST_KS_VIDEO_SRC_GET_PRIVATE (self);
  guint buf_size;
  GstCaps *caps;
  GstBuffer *buf = NULL;
  GstFlowReturn result;
  GstClockTime presentation_time;
  gulong error_code;
  gchar *error_str;

  g_assert (priv->device != NULL);

  if (!gst_ks_video_device_has_caps (priv->device))
    goto error_no_caps;

  buf_size = gst_ks_video_device_get_frame_size (priv->device);
  g_assert (buf_size);

  caps = gst_pad_get_negotiated_caps (GST_BASE_SRC_PAD (self));
  if (caps == NULL)
    goto error_no_caps;
  result = gst_pad_alloc_buffer (GST_BASE_SRC_PAD (self), priv->offset,
      buf_size, caps, &buf);
  gst_caps_unref (caps);
  if (G_UNLIKELY (result != GST_FLOW_OK))
    goto error_alloc_buffer;

  do {
    gulong bytes_read;

    result = gst_ks_video_device_read_frame (priv->device,
        GST_BUFFER_DATA (buf), buf_size, &bytes_read, &presentation_time,
        &error_code, &error_str);
    if (G_UNLIKELY (result != GST_FLOW_OK))
      goto error_read_frame;

    GST_BUFFER_SIZE (buf) = bytes_read;
  }
  while (!gst_ks_video_src_timestamp_buffer (self, buf, presentation_time));

  if (G_UNLIKELY (priv->do_stats))
    gst_ks_video_src_update_statistics (self);

  gst_ks_video_device_postprocess_frame (priv->device,
      GST_BUFFER_DATA (buf), GST_BUFFER_SIZE (buf));

  *buffer = buf;
  return GST_FLOW_OK;

  /* ERRORS */
error_no_caps:
  {
    GST_ELEMENT_ERROR (self, CORE, NEGOTIATION,
        ("not negotiated"), ("maybe setcaps failed?"));

    return GST_FLOW_ERROR;
  }
error_alloc_buffer:
  {
    GST_ELEMENT_ERROR (self, CORE, PAD, ("alloc_buffer failed"), (NULL));

    return result;
  }
error_read_frame:
  {
    if (result != GST_FLOW_WRONG_STATE && result != GST_FLOW_UNEXPECTED) {
      GST_ELEMENT_ERROR (self, RESOURCE, READ,
          ("read failed: %s [0x%08x]", error_str, error_code),
          ("gst_ks_video_device_read_frame failed"));
    }

    g_free (error_str);
    gst_buffer_unref (buf);

    return result;
  }
}

static gboolean
plugin_init (GstPlugin * plugin)
{
  return gst_element_register (plugin, "ksvideosrc",
      GST_RANK_NONE, GST_TYPE_KS_VIDEO_SRC);
}

GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
    GST_VERSION_MINOR,
    "winks",
    "Windows kernel streaming plugin",
    plugin_init, VERSION, "LGPL", "GStreamer", "http://gstreamer.net/")