1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> 2<HTML 3><HEAD 4><TITLE 5>Querying Capabilities</TITLE 6><META 7NAME="GENERATOR" 8CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK 9REL="HOME" 10TITLE="Video for Linux Two API Specification" 11HREF="book1.htm"><LINK 12REL="UP" 13TITLE="Common API Elements" 14HREF="c174.htm"><LINK 15REL="PREVIOUS" 16TITLE="Common API Elements" 17HREF="c174.htm"><LINK 18REL="NEXT" 19TITLE="Application Priority" 20HREF="x294.htm"></HEAD 21><BODY 22CLASS="SECTION" 23BGCOLOR="#FFFFFF" 24TEXT="#000000" 25LINK="#0000FF" 26VLINK="#840084" 27ALINK="#0000FF" 28><DIV 29CLASS="NAVHEADER" 30><TABLE 31SUMMARY="Header navigation table" 32WIDTH="100%" 33BORDER="0" 34CELLPADDING="0" 35CELLSPACING="0" 36><TR 37><TH 38COLSPAN="3" 39ALIGN="center" 40>Video for Linux Two API Specification: Revision 0.24</TH 41></TR 42><TR 43><TD 44WIDTH="10%" 45ALIGN="left" 46VALIGN="bottom" 47><A 48HREF="c174.htm" 49ACCESSKEY="P" 50>Prev</A 51></TD 52><TD 53WIDTH="80%" 54ALIGN="center" 55VALIGN="bottom" 56>Chapter 1. Common API Elements</TD 57><TD 58WIDTH="10%" 59ALIGN="right" 60VALIGN="bottom" 61><A 62HREF="x294.htm" 63ACCESSKEY="N" 64>Next</A 65></TD 66></TR 67></TABLE 68><HR 69ALIGN="LEFT" 70WIDTH="100%"></DIV 71><DIV 72CLASS="SECTION" 73><H1 74CLASS="SECTION" 75><A 76NAME="QUERYCAP" 77>1.2. Querying Capabilities</A 78></H1 79><P 80>Because V4L2 covers a wide variety of devices not all 81aspects of the API are equally applicable to all types of devices. 82Furthermore devices of the same type have different capabilities and 83this specification permits the omission of a few complicated and less 84important parts of the API.</P 85><P 86>The <A 87HREF="r13105.htm" 88><CODE 89CLASS="CONSTANT" 90>VIDIOC_QUERYCAP</CODE 91></A 92> ioctl is available to check if the kernel 93device is compatible with this specification, and to query the <A 94HREF="c6488.htm" 95>functions</A 96> and <A 97HREF="c5742.htm" 98>I/O 99methods</A 100> supported by the device. Other features can be queried 101by calling the respective ioctl, for example <A 102HREF="r8936.htm" 103><CODE 104CLASS="CONSTANT" 105>VIDIOC_ENUMINPUT</CODE 106></A 107> 108to learn about the number, types and names of video connectors on the 109device. Although abstraction is a major objective of this API, the 110ioctl also allows driver specific applications to reliable identify 111the driver.</P 112><P 113>All V4L2 drivers must support 114<CODE 115CLASS="CONSTANT" 116>VIDIOC_QUERYCAP</CODE 117>. Applications should always call 118this ioctl after opening the device.</P 119></DIV 120><DIV 121CLASS="NAVFOOTER" 122><HR 123ALIGN="LEFT" 124WIDTH="100%"><TABLE 125SUMMARY="Footer navigation table" 126WIDTH="100%" 127BORDER="0" 128CELLPADDING="0" 129CELLSPACING="0" 130><TR 131><TD 132WIDTH="33%" 133ALIGN="left" 134VALIGN="top" 135><A 136HREF="c174.htm" 137ACCESSKEY="P" 138>Prev</A 139></TD 140><TD 141WIDTH="34%" 142ALIGN="center" 143VALIGN="top" 144><A 145HREF="book1.htm" 146ACCESSKEY="H" 147>Home</A 148></TD 149><TD 150WIDTH="33%" 151ALIGN="right" 152VALIGN="top" 153><A 154HREF="x294.htm" 155ACCESSKEY="N" 156>Next</A 157></TD 158></TR 159><TR 160><TD 161WIDTH="33%" 162ALIGN="left" 163VALIGN="top" 164>Common API Elements</TD 165><TD 166WIDTH="34%" 167ALIGN="center" 168VALIGN="top" 169><A 170HREF="c174.htm" 171ACCESSKEY="U" 172>Up</A 173></TD 174><TD 175WIDTH="33%" 176ALIGN="right" 177VALIGN="top" 178>Application Priority</TD 179></TR 180></TABLE 181></DIV 182></BODY 183></HTML 184> 185