1.. Permission is granted to copy, distribute and/or modify this 2.. document under the terms of the GNU Free Documentation License, 3.. Version 1.1 or any later version published by the Free Software 4.. Foundation, with no Invariant Sections, no Front-Cover Texts 5.. and no Back-Cover Texts. A copy of the license is included at 6.. Documentation/userspace-api/media/fdl-appendix.rst. 7.. 8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections 9 10.. _streaming-par: 11 12******************** 13Streaming Parameters 14******************** 15 16Streaming parameters are intended to optimize the video capture process 17as well as I/O. Presently applications can request a high quality 18capture mode with the :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl. 19 20The current video standard determines a nominal number of frames per 21second. If less than this number of frames is to be captured or output, 22applications can request frame skipping or duplicating on the driver 23side. This is especially useful when using the 24:ref:`read() <func-read>` or :ref:`write() <func-write>`, which are 25not augmented by timestamps or sequence counters, and to avoid 26unnecessary data copying. 27 28Finally these ioctls can be used to determine the number of buffers used 29internally by a driver in read/write mode. For implications see the 30section discussing the :ref:`read() <func-read>` function. 31 32To get and set the streaming parameters applications call the 33:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and 34:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take 35a pointer to a struct :c:type:`v4l2_streamparm`, which 36contains a union holding separate parameters for input and output 37devices. 38 39These ioctls are optional, drivers need not implement them. If so, they 40return the ``EINVAL`` error code. 41