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