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>Streaming Parameters</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="Image Cropping, Insertion and Scaling" 17HREF="x1904.htm"><LINK 18REL="NEXT" 19TITLE="Image Formats" 20HREF="c2030.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="x1904.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="c2030.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="STREAMING-PAR" 77>1.12. Streaming Parameters</A 78></H1 79><P 80>Streaming parameters are intended to optimize the video 81capture process as well as I/O. Presently applications can request a 82high quality capture mode with the <A 83HREF="r11680.htm" 84><CODE 85CLASS="CONSTANT" 86>VIDIOC_S_PARM</CODE 87></A 88> ioctl.</P 89><P 90>The current video standard determines a nominal number of 91frames per second. If less than this number of frames is to be 92captured or output, applications can request frame skipping or 93duplicating on the driver side. This is especially useful when using 94the <A 95HREF="r14264.htm" 96><CODE 97CLASS="FUNCTION" 98>read()</CODE 99></A 100> or <A 101HREF="r14496.htm" 102><CODE 103CLASS="FUNCTION" 104>write()</CODE 105></A 106>, which are not augmented by timestamps 107or sequence counters, and to avoid unneccessary data copying.</P 108><P 109>Finally these ioctls can be used to determine the number of 110buffers used internally by a driver in read/write mode. For 111implications see the section discussing the <A 112HREF="r14264.htm" 113><CODE 114CLASS="FUNCTION" 115>read()</CODE 116></A 117> 118function.</P 119><P 120>To get and set the streaming parameters applications call 121the <A 122HREF="r11680.htm" 123><CODE 124CLASS="CONSTANT" 125>VIDIOC_G_PARM</CODE 126></A 127> and <A 128HREF="r11680.htm" 129><CODE 130CLASS="CONSTANT" 131>VIDIOC_S_PARM</CODE 132></A 133> ioctl, respectively. They take 134a pointer to a struct <A 135HREF="r11680.htm#V4L2-STREAMPARM" 136>v4l2_streamparm</A 137>, which contains a union holding 138separate parameters for input and output devices.</P 139><P 140>These ioctls are optional, drivers need not implement 141them. If so, they return the <SPAN 142CLASS="ERRORCODE" 143>EINVAL</SPAN 144> error code.</P 145></DIV 146><DIV 147CLASS="NAVFOOTER" 148><HR 149ALIGN="LEFT" 150WIDTH="100%"><TABLE 151SUMMARY="Footer navigation table" 152WIDTH="100%" 153BORDER="0" 154CELLPADDING="0" 155CELLSPACING="0" 156><TR 157><TD 158WIDTH="33%" 159ALIGN="left" 160VALIGN="top" 161><A 162HREF="x1904.htm" 163ACCESSKEY="P" 164>Prev</A 165></TD 166><TD 167WIDTH="34%" 168ALIGN="center" 169VALIGN="top" 170><A 171HREF="book1.htm" 172ACCESSKEY="H" 173>Home</A 174></TD 175><TD 176WIDTH="33%" 177ALIGN="right" 178VALIGN="top" 179><A 180HREF="c2030.htm" 181ACCESSKEY="N" 182>Next</A 183></TD 184></TR 185><TR 186><TD 187WIDTH="33%" 188ALIGN="left" 189VALIGN="top" 190>Image Cropping, Insertion and Scaling</TD 191><TD 192WIDTH="34%" 193ALIGN="center" 194VALIGN="top" 195><A 196HREF="c174.htm" 197ACCESSKEY="U" 198>Up</A 199></TD 200><TD 201WIDTH="33%" 202ALIGN="right" 203VALIGN="top" 204>Image Formats</TD 205></TR 206></TABLE 207></DIV 208></BODY 209></HTML 210> 211