media/v4l/func-read.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
4 .. _func-read:
13 v4l2-read - Read from a V4L2 device
18 .. code-block:: c
34   Max number of bytes to read
45 :c:func:`read()` call will provide at most one frame (two fields)
65 reading, or the capture rate must fall below the nominal frame rate of
72 previously, not read frame, and returns the frame being received at the
76 :c:func:`read()` call. The frame being received at :c:func:`read()`
77 time is discarded, returning the following frame instead. Again this
79 nominal frame rate. An example of this model is the video read mode of
89 Applications can get and set the number of buffers used internally by
98 On success, the number of bytes read is returned. It is not an error if
99 this number is smaller than the number of bytes requested, or the amount
100 of data required for one frame. This may happen for example because
101 :c:func:`read()` was interrupted by a signal. On error, -1 is
103 the next read will start at the beginning of a new frame. Possible error
107     Non-blocking I/O has been selected using O_NONBLOCK and no data was
112     the process already has the maximum number of files open.