v4l2capability

The v4l2capability structure is a key component within the Video for Linux Two (V4L2) subsystem in the Linux kernel. It is used to query and report the capabilities of a V4L2 device. This structure is fundamental for applications to understand what functionalities a particular video device offers and how to interact with it.

When an application wants to know what a V4L2 device can do, it typically performs an ioctl (input/output control) call, specifically the VIDIOC_QUERYCAP ioctl. The application provides a pointer to a v4l2capability structure, and the kernel populates this structure with information about the device.

The v4l2capability structure contains several important fields. The driver field identifies the name of the V4L2 driver associated with the device. The card field describes the name of the hardware device itself. The bus_info field provides details about how the device is connected to the system, such as USB port or PCI address.

Crucially, the v4l2capability structure includes flags that indicate the device's capabilities. These flags, defined by constants like V4L2_CAP_VIDEO_CAPTURE, V4L2_CAP_VIDEO_OUTPUT, V4L2_CAP_VBI_CAPTURE, and V4L2_CAP_STREAMING, inform the application whether the device supports video recording, video playback, vertical blanking interval capture, or streaming operations. By examining these flags, applications can dynamically adapt their behavior and present only the relevant features to the user. This mechanism ensures that software can interact correctly and efficiently with a wide range of V4L2-compatible hardware.