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- .. -*- coding: utf-8; mode: rst -*-
- .. _querycap:
- *********************
- Querying Capabilities
- *********************
- Because V4L2 covers a wide variety of devices not all aspects of the API
- are equally applicable to all types of devices. Furthermore devices of
- the same type have different capabilities and this specification permits
- the omission of a few complicated and less important parts of the API.
- The :ref:`VIDIOC_QUERYCAP` ioctl is available to
- check if the kernel device is compatible with this specification, and to
- query the :ref:`functions <devices>` and :ref:`I/O methods <io>`
- supported by the device.
- Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP`
- will return the V4L2 API version used by the driver, with generally
- matches the Kernel version. There's no need of using
- :ref:`VIDIOC_QUERYCAP` to check if a specific ioctl
- is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't
- provide support for an ioctl.
- Other features can be queried by calling the respective ioctl, for
- example :ref:`VIDIOC_ENUMINPUT` to learn about the
- number, types and names of video connectors on the device. Although
- abstraction is a major objective of this API, the
- :ref:`VIDIOC_QUERYCAP` ioctl also allows driver
- specific applications to reliably identify the driver.
- All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`.
- Applications should always call this ioctl after opening the device.
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