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| >Video for Linux Two API Specification: Revision 0.24</TH |
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| ><H1 |
| ><A |
| NAME="VIDIOC-STREAMON" |
| ></A |
| >ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</H1 |
| ><DIV |
| CLASS="REFNAMEDIV" |
| ><A |
| NAME="AEN13821" |
| ></A |
| ><H2 |
| >Name</H2 |
| >VIDIOC_STREAMON, VIDIOC_STREAMOFF -- Start or stop streaming I/O</DIV |
| ><DIV |
| CLASS="REFSYNOPSISDIV" |
| ><A |
| NAME="AEN13825" |
| ></A |
| ><H2 |
| >Synopsis</H2 |
| ><DIV |
| CLASS="FUNCSYNOPSIS" |
| ><P |
| ></P |
| ><A |
| NAME="AEN13826" |
| ></A |
| ><P |
| ><CODE |
| ><CODE |
| CLASS="FUNCDEF" |
| >int ioctl</CODE |
| >(int fd, int request, const int *argp);</CODE |
| ></P |
| ><P |
| ></P |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13836" |
| ></A |
| ><H2 |
| >Arguments</H2 |
| ><P |
| ></P |
| ><DIV |
| CLASS="VARIABLELIST" |
| ><DL |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >fd</CODE |
| ></DT |
| ><DD |
| ><P |
| >File descriptor returned by <A |
| HREF="r14090.htm" |
| ><CODE |
| CLASS="FUNCTION" |
| >open()</CODE |
| ></A |
| >.</P |
| ></DD |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >request</CODE |
| ></DT |
| ><DD |
| ><P |
| >VIDIOC_STREAMON, VIDIOC_STREAMOFF</P |
| ></DD |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >argp</CODE |
| ></DT |
| ><DD |
| ><P |
| ></P |
| ></DD |
| ></DL |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13856" |
| ></A |
| ><H2 |
| >Description</H2 |
| ><P |
| >The <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMON</CODE |
| > and |
| <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMOFF</CODE |
| > ioctl start and stop the capture |
| or output process during streaming (<A |
| HREF="x5791.htm" |
| >memory |
| mapping</A |
| > or <A |
| HREF="x5884.htm" |
| >user pointer</A |
| >) I/O.</P |
| ><P |
| >Specifically the capture hardware is disabled and no input |
| buffers are filled (if there are any empty buffers in the incoming |
| queue) until <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMON</CODE |
| > has been called. |
| Accordingly the output hardware is disabled, no video signal is |
| produced until <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMON</CODE |
| > has been called. |
| The ioctl will succeed only when at least one output buffer is in the |
| incoming queue.</P |
| ><P |
| >The <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMOFF</CODE |
| > ioctl, apart of |
| aborting or finishing any DMA in progress, unlocks any user pointer |
| buffers locked in physical memory, and it removes all buffers from the |
| incoming and outgoing queues. That means all images captured but not |
| dequeued yet will be lost, likewise all images enqueued for output but |
| not transmitted yet. I/O returns to the same state as after calling |
| <A |
| HREF="r13696.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_REQBUFS</CODE |
| ></A |
| > and can be restarted accordingly.</P |
| ><P |
| >Both ioctls take a pointer to an integer, the desired buffer or |
| stream type. This is the same as struct <A |
| HREF="r13696.htm#V4L2-REQUESTBUFFERS" |
| >v4l2_requestbuffers</A |
| > |
| <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| >.</P |
| ><P |
| >Note applications can be preempted for unknown periods right |
| before or after the <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMON</CODE |
| > or |
| <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMOFF</CODE |
| > calls, there is no notion of |
| starting or stopping "now". Buffer timestamps can be used to |
| synchronize with other events.</P |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13876" |
| ></A |
| ><H2 |
| >Return Value</H2 |
| ><P |
| >On success <SPAN |
| CLASS="RETURNVALUE" |
| >0</SPAN |
| > is returned, on error <SPAN |
| CLASS="RETURNVALUE" |
| >-1</SPAN |
| > and the <CODE |
| CLASS="VARNAME" |
| >errno</CODE |
| > variable is set appropriately:</P |
| ><P |
| ></P |
| ><DIV |
| CLASS="VARIABLELIST" |
| ><DL |
| ><DT |
| ><SPAN |
| CLASS="ERRORCODE" |
| >EINVAL</SPAN |
| ></DT |
| ><DD |
| ><P |
| >Streaming I/O is not supported, the buffer |
| <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > is not supported, or no buffers have |
| been allocated (memory mapping) or enqueued (output) yet.</P |
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