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5>Streaming Parameters</TITLE
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40>Video for Linux Two API Specification: Revision 0.24</TH
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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&nbsp;<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
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