v4l2: add v4l2_set_frame_rate

We would like to be able to set the frame rate of video sources. This
patch adds such a function for v4l2-based video sources to use.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/lib/v4l2.c b/lib/v4l2.c
index 9030270..de6ed88 100644
--- a/lib/v4l2.c
+++ b/lib/v4l2.c
@@ -500,6 +500,26 @@ int v4l2_set_format(struct v4l2_device *dev, struct v4l2_pix_format *format)
 	return 0;
 }
 
+int v4l2_set_frame_rate(struct v4l2_device *dev, unsigned int fps)
+{
+	struct v4l2_streamparm parm;
+	int ret;
+
+	memset(&parm, 0, sizeof parm);
+	parm.type = dev->type;
+	parm.parm.capture.timeperframe.numerator = 1;
+	parm.parm.capture.timeperframe.denominator = fps;
+
+	ret = ioctl(dev->fd, VIDIOC_S_PARM, &parm);
+	if (ret < 0) {
+		printf("%s: unable to set frame rate (%d).\n", dev->name, errno);
+		return -errno;
+	}
+
+	dev->fps = fps;
+	return 0;
+}
+
 /* -----------------------------------------------------------------------------
  * Buffers management
  */
diff --git a/lib/v4l2.h b/lib/v4l2.h
index 8d7b3c5..7bacf5d 100644
--- a/lib/v4l2.h
+++ b/lib/v4l2.h
@@ -31,6 +31,7 @@ struct v4l2_device
 	struct list_entry formats;
 	struct v4l2_pix_format format;
 	struct v4l2_rect crop;
+	unsigned int fps;
 
 	struct video_buffer_set buffers;
 };
@@ -86,6 +87,19 @@ int v4l2_get_format(struct v4l2_device *dev, struct v4l2_pix_format *format);
 int v4l2_set_format(struct v4l2_device *dev, struct v4l2_pix_format *format);
 
 /*
+ * v4l2_set_frame_rate - Set the frame rate
+ * @dev: Device instance
+ * @fps: Frame rate
+ *
+ * Set the frame rate specified by @fps.
+ * The device can modify the requested format and size, in which case @dev->fps
+ * will be updated to reflect the modified setting.
+ *
+ * Return 0 on success or a negative error code on failure.
+ */
+int v4l2_set_frame_rate(struct v4l2_device *dev, unsigned int fps);
+
+/*
  * v4l2_get_crop - Retrieve the current crop rectangle
  * @dev: Device instance
  * @rect: Crop rectangle structure to be filled