summaryrefslogtreecommitdiffstats
path: root/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--Documentation/userspace-api/media/v4l/vidioc-g-parm.rst269
1 files changed, 269 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst b/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst
new file mode 100644
index 000000000..8b5600fbf
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst
@@ -0,0 +1,269 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_G_PARM:
+
+**********************************
+ioctl VIDIOC_G_PARM, VIDIOC_S_PARM
+**********************************
+
+Name
+====
+
+VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_G_PARM
+
+``int ioctl(int fd, VIDIOC_G_PARM, v4l2_streamparm *argp)``
+
+.. c:macro:: VIDIOC_S_PARM
+
+``int ioctl(int fd, VIDIOC_S_PARM, v4l2_streamparm *argp)``
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :c:func:`open()`.
+
+``argp``
+ Pointer to struct :c:type:`v4l2_streamparm`.
+
+Description
+===========
+
+Applications can request a different frame interval. The capture or
+output device will be reconfigured to support the requested frame
+interval if possible. Optionally drivers may choose to skip or
+repeat frames to achieve the requested frame interval.
+
+For stateful encoders (see :ref:`encoder`) this represents the
+frame interval that is typically embedded in the encoded video stream.
+
+Changing the frame interval shall never change the format. Changing the
+format, on the other hand, may change the frame interval.
+
+Further these ioctls can be used to determine the number of buffers used
+internally by a driver in read/write mode. For implications see the
+section discussing the :c:func:`read()` function.
+
+To get and set the streaming parameters applications call the
+:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
+:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a
+pointer to a struct :c:type:`v4l2_streamparm` which contains a
+union holding separate parameters for input and output devices.
+
+.. tabularcolumns:: |p{3.7cm}|p{3.5cm}|p{10.1cm}|
+
+.. c:type:: v4l2_streamparm
+
+.. flat-table:: struct v4l2_streamparm
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``type``
+ - The buffer (stream) type, same as struct
+ :c:type:`v4l2_format` ``type``, set by the
+ application. See :c:type:`v4l2_buf_type`.
+ * - union {
+ - ``parm``
+ * - struct :c:type:`v4l2_captureparm`
+ - ``capture``
+ - Parameters for capture devices, used when ``type`` is
+ ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
+ ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``.
+ * - struct :c:type:`v4l2_outputparm`
+ - ``output``
+ - Parameters for output devices, used when ``type`` is
+ ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``.
+ * - __u8
+ - ``raw_data``\ [200]
+ - A place holder for future extensions.
+ * - }
+
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
+
+.. c:type:: v4l2_captureparm
+
+.. flat-table:: struct v4l2_captureparm
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``capability``
+ - See :ref:`parm-caps`.
+ * - __u32
+ - ``capturemode``
+ - Set by drivers and applications, see :ref:`parm-flags`.
+ * - struct :c:type:`v4l2_fract`
+ - ``timeperframe``
+ - This is the desired period between successive frames captured by
+ the driver, in seconds.
+ * - :cspan:`2`
+
+ This will configure the speed at which the video source (e.g. a sensor)
+ generates video frames. If the speed is fixed, then the driver may
+ choose to skip or repeat frames in order to achieve the requested
+ frame rate.
+
+ For stateful encoders (see :ref:`encoder`) this represents the
+ frame interval that is typically embedded in the encoded video stream.
+
+ Applications store here the desired frame period, drivers return
+ the actual frame period.
+
+ Changing the video standard (also implicitly by switching
+ the video input) may reset this parameter to the nominal frame
+ period. To reset manually applications can just set this field to
+ zero.
+
+ Drivers support this function only when they set the
+ ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
+ * - __u32
+ - ``extendedmode``
+ - Custom (driver specific) streaming parameters. When unused,
+ applications and drivers must set this field to zero. Applications
+ using this field should check the driver name and version, see
+ :ref:`querycap`.
+ * - __u32
+ - ``readbuffers``
+ - Applications set this field to the desired number of buffers used
+ internally by the driver in :c:func:`read()` mode.
+ Drivers return the actual number of buffers. When an application
+ requests zero buffers, drivers should just return the current
+ setting rather than the minimum or an error code. For details see
+ :ref:`rw`.
+ * - __u32
+ - ``reserved``\ [4]
+ - Reserved for future extensions. Drivers and applications must set
+ the array to zero.
+
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
+
+.. c:type:: v4l2_outputparm
+
+.. flat-table:: struct v4l2_outputparm
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``capability``
+ - See :ref:`parm-caps`.
+ * - __u32
+ - ``outputmode``
+ - Set by drivers and applications, see :ref:`parm-flags`.
+ * - struct :c:type:`v4l2_fract`
+ - ``timeperframe``
+ - This is the desired period between successive frames output by the
+ driver, in seconds.
+ * - :cspan:`2`
+
+ The field is intended to repeat frames on the driver side in
+ :c:func:`write()` mode (in streaming mode timestamps
+ can be used to throttle the output), saving I/O bandwidth.
+
+ For stateful encoders (see :ref:`encoder`) this represents the
+ frame interval that is typically embedded in the encoded video stream
+ and it provides a hint to the encoder of the speed at which raw
+ frames are queued up to the encoder.
+
+ Applications store here the desired frame period, drivers return
+ the actual frame period.
+
+ Changing the video standard (also implicitly by switching
+ the video output) may reset this parameter to the nominal frame
+ period. To reset manually applications can just set this field to
+ zero.
+
+ Drivers support this function only when they set the
+ ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
+ * - __u32
+ - ``extendedmode``
+ - Custom (driver specific) streaming parameters. When unused,
+ applications and drivers must set this field to zero. Applications
+ using this field should check the driver name and version, see
+ :ref:`querycap`.
+ * - __u32
+ - ``writebuffers``
+ - Applications set this field to the desired number of buffers used
+ internally by the driver in :c:func:`write()` mode. Drivers
+ return the actual number of buffers. When an application requests
+ zero buffers, drivers should just return the current setting
+ rather than the minimum or an error code. For details see
+ :ref:`rw`.
+ * - __u32
+ - ``reserved``\ [4]
+ - Reserved for future extensions. Drivers and applications must set
+ the array to zero.
+
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
+
+.. _parm-caps:
+
+.. flat-table:: Streaming Parameters Capabilities
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+ * - ``V4L2_CAP_TIMEPERFRAME``
+ - 0x1000
+ - The frame period can be modified by setting the ``timeperframe``
+ field.
+
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
+
+.. _parm-flags:
+
+.. flat-table:: Capture Parameters Flags
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+ * - ``V4L2_MODE_HIGHQUALITY``
+ - 0x0001
+ - High quality imaging mode. High quality mode is intended for still
+ imaging applications. The idea is to get the best possible image
+ quality that the hardware can deliver. It is not defined how the
+ driver writer may achieve that; it will depend on the hardware and
+ the ingenuity of the driver writer. High quality mode is a
+ different mode from the regular motion video capture modes. In
+ high quality mode:
+
+ - The driver may be able to capture higher resolutions than for
+ motion capture.
+
+ - The driver may support fewer pixel formats than motion capture
+ (eg; true color).
+
+ - The driver may capture and arithmetically combine multiple
+ successive fields or frames to remove color edge artifacts and
+ reduce the noise in the video data.
+
+ - The driver may capture images in slices like a scanner in order
+ to handle larger format images than would otherwise be
+ possible.
+
+ - An image capture operation may be significantly slower than
+ motion capture.
+
+ - Moving objects in the image might have excessive motion blur.
+
+ - Capture might only work through the :c:func:`read()` call.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.