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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/vidioc-querystd.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-querystd.rst | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-querystd.rst b/Documentation/userspace-api/media/v4l/vidioc-querystd.rst new file mode 100644 index 000000000..4a88287d8 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-querystd.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _VIDIOC_QUERYSTD: + +********************************************* +ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD +********************************************* + +Name +==== + +VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input + +Synopsis +======== + +.. c:macro:: VIDIOC_QUERYSTD + +``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)`` + +.. c:macro:: VIDIOC_SUBDEV_QUERYSTD + +``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to :c:type:`v4l2_std_id`. + +Description +=========== + +The hardware may be able to detect the current video standard +automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a +pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver +stores here a set of candidates, this can be a single flag or a set of +supported standards if for example the hardware can only distinguish +between 50 and 60 Hz systems. If no signal was detected, then the driver +will return V4L2_STD_UNKNOWN. When detection is not possible or fails, +the set must contain all standards supported by the current video input +or output. + +.. note:: + + Drivers shall *not* switch the video standard + automatically if a new video standard is detected. Instead, drivers + should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support + this) and expect that userspace will take action by calling + :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean + different buffer sizes as well, and you cannot change buffer sizes on + the fly. In general, applications that receive the Source Change event + will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video + standard is valid they will have to stop streaming, set the new + standard, allocate new buffers and start streaming again. + +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. + +ENODATA + Standard video timings are not supported for this input or output. |