1059b1c5bSMauro Carvalho Chehab.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2407e84cdSMauro Carvalho Chehab.. c:namespace:: V4L 354f38fcaSMauro Carvalho Chehab 454f38fcaSMauro Carvalho Chehab.. _streaming-par: 554f38fcaSMauro Carvalho Chehab 654f38fcaSMauro Carvalho Chehab******************** 754f38fcaSMauro Carvalho ChehabStreaming Parameters 854f38fcaSMauro Carvalho Chehab******************** 954f38fcaSMauro Carvalho Chehab 1054f38fcaSMauro Carvalho ChehabStreaming parameters are intended to optimize the video capture process 1154f38fcaSMauro Carvalho Chehabas well as I/O. Presently applications can request a high quality 1254f38fcaSMauro Carvalho Chehabcapture mode with the :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl. 1354f38fcaSMauro Carvalho Chehab 1454f38fcaSMauro Carvalho ChehabThe current video standard determines a nominal number of frames per 1554f38fcaSMauro Carvalho Chehabsecond. If less than this number of frames is to be captured or output, 1654f38fcaSMauro Carvalho Chehabapplications can request frame skipping or duplicating on the driver 1754f38fcaSMauro Carvalho Chehabside. This is especially useful when using the 18407e84cdSMauro Carvalho Chehab:c:func:`read()` or :c:func:`write()`, which are 1954f38fcaSMauro Carvalho Chehabnot augmented by timestamps or sequence counters, and to avoid 2054f38fcaSMauro Carvalho Chehabunnecessary data copying. 2154f38fcaSMauro Carvalho Chehab 2254f38fcaSMauro Carvalho ChehabFinally these ioctls can be used to determine the number of buffers used 2354f38fcaSMauro Carvalho Chehabinternally by a driver in read/write mode. For implications see the 24407e84cdSMauro Carvalho Chehabsection discussing the :c:func:`read()` function. 2554f38fcaSMauro Carvalho Chehab 2654f38fcaSMauro Carvalho ChehabTo get and set the streaming parameters applications call the 2754f38fcaSMauro Carvalho Chehab:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and 2854f38fcaSMauro Carvalho Chehab:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take 2954f38fcaSMauro Carvalho Chehaba pointer to a struct :c:type:`v4l2_streamparm`, which 3054f38fcaSMauro Carvalho Chehabcontains a union holding separate parameters for input and output 3154f38fcaSMauro Carvalho Chehabdevices. 3254f38fcaSMauro Carvalho Chehab 3354f38fcaSMauro Carvalho ChehabThese ioctls are optional, drivers need not implement them. If so, they 3454f38fcaSMauro Carvalho Chehabreturn the ``EINVAL`` error code. 35