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     40 >Video for Linux Two API Specification: Revision 0.24</TH
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     71 ><H1
     72 ><A
     73 NAME="VIDIOC-STREAMON"
     74 ></A
     75 >ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</H1
     76 ><DIV
     77 CLASS="REFNAMEDIV"
     78 ><A
     79 NAME="AEN13821"
     80 ></A
     81 ><H2
     82 >Name</H2
     83 >VIDIOC_STREAMON, VIDIOC_STREAMOFF&nbsp;--&nbsp;Start or stop streaming I/O</DIV
     84 ><DIV
     85 CLASS="REFSYNOPSISDIV"
     86 ><A
     87 NAME="AEN13825"
     88 ></A
     89 ><H2
     90 >Synopsis</H2
     91 ><DIV
     92 CLASS="FUNCSYNOPSIS"
     93 ><P
     94 ></P
     95 ><A
     96 NAME="AEN13826"
     97 ></A
     98 ><P
     99 ><CODE
    100 ><CODE
    101 CLASS="FUNCDEF"
    102 >int ioctl</CODE
    103 >(int fd, int request, const int *argp);</CODE
    104 ></P
    105 ><P
    106 ></P
    107 ></DIV
    108 ></DIV
    109 ><DIV
    110 CLASS="REFSECT1"
    111 ><A
    112 NAME="AEN13836"
    113 ></A
    114 ><H2
    115 >Arguments</H2
    116 ><P
    117 ></P
    118 ><DIV
    119 CLASS="VARIABLELIST"
    120 ><DL
    121 ><DT
    122 ><CODE
    123 CLASS="PARAMETER"
    124 >fd</CODE
    125 ></DT
    126 ><DD
    127 ><P
    128 >File descriptor returned by <A
    129 HREF="r14090.htm"
    130 ><CODE
    131 CLASS="FUNCTION"
    132 >open()</CODE
    133 ></A
    134 >.</P
    135 ></DD
    136 ><DT
    137 ><CODE
    138 CLASS="PARAMETER"
    139 >request</CODE
    140 ></DT
    141 ><DD
    142 ><P
    143 >VIDIOC_STREAMON, VIDIOC_STREAMOFF</P
    144 ></DD
    145 ><DT
    146 ><CODE
    147 CLASS="PARAMETER"
    148 >argp</CODE
    149 ></DT
    150 ><DD
    151 ><P
    152 ></P
    153 ></DD
    154 ></DL
    155 ></DIV
    156 ></DIV
    157 ><DIV
    158 CLASS="REFSECT1"
    159 ><A
    160 NAME="AEN13856"
    161 ></A
    162 ><H2
    163 >Description</H2
    164 ><P
    165 >The <CODE
    166 CLASS="CONSTANT"
    167 >VIDIOC_STREAMON</CODE
    168 > and
    169 <CODE
    170 CLASS="CONSTANT"
    171 >VIDIOC_STREAMOFF</CODE
    172 > ioctl start and stop the capture
    173 or output process during streaming (<A
    174 HREF="x5791.htm"
    175 >memory
    176 mapping</A
    177 > or <A
    178 HREF="x5884.htm"
    179 >user pointer</A
    180 >) I/O.</P
    181 ><P
    182 >Specifically the capture hardware is disabled and no input
    183 buffers are filled (if there are any empty buffers in the incoming
    184 queue) until <CODE
    185 CLASS="CONSTANT"
    186 >VIDIOC_STREAMON</CODE
    187 > has been called.
    188 Accordingly the output hardware is disabled, no video signal is
    189 produced until <CODE
    190 CLASS="CONSTANT"
    191 >VIDIOC_STREAMON</CODE
    192 > has been called.
    193 The ioctl will succeed only when at least one output buffer is in the
    194 incoming queue.</P
    195 ><P
    196 >The <CODE
    197 CLASS="CONSTANT"
    198 >VIDIOC_STREAMOFF</CODE
    199 > ioctl, apart of
    200 aborting or finishing any DMA in progress, unlocks any user pointer
    201 buffers locked in physical memory, and it removes all buffers from the
    202 incoming and outgoing queues. That means all images captured but not
    203 dequeued yet will be lost, likewise all images enqueued for output but
    204 not transmitted yet. I/O returns to the same state as after calling
    205 <A
    206 HREF="r13696.htm"
    207 ><CODE
    208 CLASS="CONSTANT"
    209 >VIDIOC_REQBUFS</CODE
    210 ></A
    211 > and can be restarted accordingly.</P
    212 ><P
    213 >Both ioctls take a pointer to an integer, the desired buffer or
    214 stream type. This is the same as struct&nbsp;<A
    215 HREF="r13696.htm#V4L2-REQUESTBUFFERS"
    216 >v4l2_requestbuffers</A
    217 >
    218 <CODE
    219 CLASS="STRUCTFIELD"
    220 >type</CODE
    221 >.</P
    222 ><P
    223 >Note applications can be preempted for unknown periods right
    224 before or after the <CODE
    225 CLASS="CONSTANT"
    226 >VIDIOC_STREAMON</CODE
    227 > or
    228 <CODE
    229 CLASS="CONSTANT"
    230 >VIDIOC_STREAMOFF</CODE
    231 > calls, there is no notion of
    232 starting or stopping "now". Buffer timestamps can be used to
    233 synchronize with other events.</P
    234 ></DIV
    235 ><DIV
    236 CLASS="REFSECT1"
    237 ><A
    238 NAME="AEN13876"
    239 ></A
    240 ><H2
    241 >Return Value</H2
    242 ><P
    243 >On success <SPAN
    244 CLASS="RETURNVALUE"
    245 >0</SPAN
    246 > is returned, on error <SPAN
    247 CLASS="RETURNVALUE"
    248 >-1</SPAN
    249 > and the <CODE
    250 CLASS="VARNAME"
    251 >errno</CODE
    252 > variable is set appropriately:</P
    253 ><P
    254 ></P
    255 ><DIV
    256 CLASS="VARIABLELIST"
    257 ><DL
    258 ><DT
    259 ><SPAN
    260 CLASS="ERRORCODE"
    261 >EINVAL</SPAN
    262 ></DT
    263 ><DD
    264 ><P
    265 >Streaming I/O is not supported, the buffer
    266 <CODE
    267 CLASS="STRUCTFIELD"
    268 >type</CODE
    269 > is not supported, or no buffers have
    270 been allocated (memory mapping) or enqueued (output) yet.</P
    271 ></DD
    272 ></DL
    273 ></DIV
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