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| >1.2. Querying Capabilities</A |
| ></H1 |
| ><P |
| >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.</P |
| ><P |
| >The <A |
| HREF="r13105.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_QUERYCAP</CODE |
| ></A |
| > ioctl is available to check if the kernel |
| device is compatible with this specification, and to query the <A |
| HREF="c6488.htm" |
| >functions</A |
| > and <A |
| HREF="c5742.htm" |
| >I/O |
| methods</A |
| > supported by the device. Other features can be queried |
| by calling the respective ioctl, for example <A |
| HREF="r8936.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_ENUMINPUT</CODE |
| ></A |
| > |
| to learn about the number, types and names of video connectors on the |
| device. Although abstraction is a major objective of this API, the |
| ioctl also allows driver specific applications to reliable identify |
| the driver.</P |
| ><P |
| >All V4L2 drivers must support |
| <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_QUERYCAP</CODE |
| >. Applications should always call |
| this ioctl after opening the device.</P |
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