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 >Relation of V4L2 to other Linux multimedia APIs</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="Changes" 14 HREF="c14595.htm"><LINK 15 REL="PREVIOUS" 16 TITLE="Changes of the V4L2 API" 17 HREF="x15446.htm"><LINK 18 REL="NEXT" 19 TITLE="Experimental API Elements" 20 HREF="x16453.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="x15446.htm" 49 ACCESSKEY="P" 50 >Prev</A 51 ></TD 52 ><TD 53 WIDTH="80%" 54 ALIGN="center" 55 VALIGN="bottom" 56 >Chapter 6. Changes</TD 57 ><TD 58 WIDTH="10%" 59 ALIGN="right" 60 VALIGN="bottom" 61 ><A 62 HREF="x16453.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="OTHER" 77 >6.3. Relation of V4L2 to other Linux multimedia APIs</A 78 ></H1 79 ><DIV 80 CLASS="SECTION" 81 ><H2 82 CLASS="SECTION" 83 ><A 84 NAME="XVIDEO" 85 >6.3.1. X Video Extension</A 86 ></H2 87 ><P 88 >The X Video Extension (abbreviated XVideo or just Xv) is 89 an extension of the X Window system, implemented for example by the 90 XFree86 project. Its scope is similar to V4L2, an API to video capture 91 and output devices for X clients. Xv allows applications to display 92 live video in a window, send window contents to a TV output, and 93 capture or output still images in XPixmaps<A 94 NAME="AEN16435" 95 HREF="x16430.htm#FTN.AEN16435" 96 ><SPAN 97 CLASS="footnote" 98 >[1]</SPAN 99 ></A 100 >. With their implementation XFree86 makes the 101 extension available across many operating systems and 102 architectures.</P 103 ><P 104 >Because the driver is embedded into the X server Xv has a 105 number of advantages over the V4L2 <A 106 HREF="x6570.htm" 107 >video 108 overlay interface</A 109 >. The driver can easily determine the overlay 110 target, i. e. visible graphics memory or off-screen buffers for a 111 destructive overlay. It can program the RAMDAC for a non-destructive 112 overlay, scaling or color-keying, or the clipping functions of the 113 video capture hardware, always in sync with drawing operations or 114 windows moving or changing their stacking order.</P 115 ><P 116 >To combine the advantages of Xv and V4L a special Xv 117 driver exists in XFree86 and XOrg, just programming any overlay capable 118 Video4Linux device it finds. To enable it 119 <TT 120 CLASS="FILENAME" 121 >/etc/X11/XF86Config</TT 122 > must contain these lines:</P 123 ><P 124 ><PRE 125 CLASS="SCREEN" 126 >Section "Module" 127 Load "v4l" 128 EndSection</PRE 129 ></P 130 ><P 131 >As of XFree86 4.2 this driver still supports only V4L 132 ioctls, however it should work just fine with all V4L2 devices through 133 the V4L2 backward-compatibility layer. Since V4L2 permits multiple 134 opens it is possible (if supported by the V4L2 driver) to capture 135 video while an X client requested video overlay. Restrictions of 136 simultaneous capturing and overlay are discussed in <A 137 HREF="x6570.htm" 138 >Section 4.2</A 139 > apply.</P 140 ><P 141 >Only marginally related to V4L2, XFree86 extended Xv to 142 support hardware YUV to RGB conversion and scaling for faster video 143 playback, and added an interface to MPEG-2 decoding hardware. This API 144 is useful to display images captured with V4L2 devices.</P 145 ></DIV 146 ><DIV 147 CLASS="SECTION" 148 ><H2 149 CLASS="SECTION" 150 ><A 151 NAME="AEN16446" 152 >6.3.2. Digital Video</A 153 ></H2 154 ><P 155 >V4L2 does not support digital terrestrial, cable or 156 satellite broadcast. A separate project aiming at digital receivers 157 exists. You can find its homepage at <A 158 HREF="http://linuxtv.org" 159 TARGET="_top" 160 >http://linuxtv.org</A 161 >. The Linux DVB API 162 has no connection to the V4L2 API except that drivers for hybrid 163 hardware may support both.</P 164 ></DIV 165 ><DIV 166 CLASS="SECTION" 167 ><H2 168 CLASS="SECTION" 169 ><A 170 NAME="AEN16450" 171 >6.3.3. Audio Interfaces</A 172 ></H2 173 ><P 174 >[to do - OSS/ALSA]</P 175 ></DIV 176 ></DIV 177 ><H3 178 CLASS="FOOTNOTES" 179 >Notes</H3 180 ><TABLE 181 BORDER="0" 182 CLASS="FOOTNOTES" 183 WIDTH="100%" 184 ><TR 185 ><TD 186 ALIGN="LEFT" 187 VALIGN="TOP" 188 WIDTH="5%" 189 ><A 190 NAME="FTN.AEN16435" 191 HREF="x16430.htm#AEN16435" 192 ><SPAN 193 CLASS="footnote" 194 >[1]</SPAN 195 ></A 196 ></TD 197 ><TD 198 ALIGN="LEFT" 199 VALIGN="TOP" 200 WIDTH="95%" 201 ><P 202 >This is not implemented in XFree86.</P 203 ></TD 204 ></TR 205 ></TABLE 206 ><DIV 207 CLASS="NAVFOOTER" 208 ><HR 209 ALIGN="LEFT" 210 WIDTH="100%"><TABLE 211 SUMMARY="Footer navigation table" 212 WIDTH="100%" 213 BORDER="0" 214 CELLPADDING="0" 215 CELLSPACING="0" 216 ><TR 217 ><TD 218 WIDTH="33%" 219 ALIGN="left" 220 VALIGN="top" 221 ><A 222 HREF="x15446.htm" 223 ACCESSKEY="P" 224 >Prev</A 225 ></TD 226 ><TD 227 WIDTH="34%" 228 ALIGN="center" 229 VALIGN="top" 230 ><A 231 HREF="book1.htm" 232 ACCESSKEY="H" 233 >Home</A 234 ></TD 235 ><TD 236 WIDTH="33%" 237 ALIGN="right" 238 VALIGN="top" 239 ><A 240 HREF="x16453.htm" 241 ACCESSKEY="N" 242 >Next</A 243 ></TD 244 ></TR 245 ><TR 246 ><TD 247 WIDTH="33%" 248 ALIGN="left" 249 VALIGN="top" 250 >Changes of the V4L2 API</TD 251 ><TD 252 WIDTH="34%" 253 ALIGN="center" 254 VALIGN="top" 255 ><A 256 HREF="c14595.htm" 257 ACCESSKEY="U" 258 >Up</A 259 ></TD 260 ><TD 261 WIDTH="33%" 262 ALIGN="right" 263 VALIGN="top" 264 >Experimental API Elements</TD 265 ></TR 266 ></TABLE 267 ></DIV 268 ></BODY 269 ></HTML 270 > 271
