media/v4l/func-read.xml

1 <refentry id="func-read">
8     <refname>v4l2-read</refname>
54 <parameter>fd</parameter> into the buffer starting at
55 <parameter>buf</parameter>. The layout of the data in the buffer is
61 <function>read()</function> call will provide at most one frame (two
66 given to the &func-open; function it
68 &func-select; or &func-poll; functions
79 buffer being filled. Using a single buffer the driver will stop
80 capturing when the application starts reading the buffer until the
83 the nominal frame rate of the video standard.</para>
89 frames keeps capturing into an internal buffer, continuously
90 overwriting the previously, not read frame, and returns the frame
95 the next <function>read()</function> call. The frame being received at
97 frame instead. Again this implies a reduction of the capture rate to
98 one half or less of the nominal frame rate. An example of this model
103     <para>In the multiple buffer model drivers maintain a ring of
104 internal buffers, automatically advancing to the next free buffer.
110 internally by the driver with the &VIDIOC-G-PARM; and &VIDIOC-S-PARM;
121 or the amount of data required for one frame. This may happen for
123 signal. On error, -1 is returned, and the <varname>errno</varname>
125 at the beginning of a new frame. Possible error codes are:</para>
131 	  <para>Non-blocking I/O has been selected using