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-.. Permission is granted to copy, distribute and/or modify this
-.. document under the terms of the GNU Free Documentation License,
-.. Version 1.1 or any later version published by the Free Software
-.. Foundation, with no Invariant Sections, no Front-Cover Texts
-.. and no Back-Cover Texts. A copy of the license is included at
-.. Documentation/media/uapi/fdl-appendix.rst.
-..
-.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
-
-.. _libv4l-introduction:
-
-************
-Introduction
-************
-
-libv4l is a collection of libraries which adds a thin abstraction layer
-on top of video4linux2 devices. The purpose of this (thin) layer is to
-make it easy for application writers to support a wide variety of
-devices without having to write separate code for different devices in
-the same class.
-
-An example of using libv4l is provided by
-:ref:`v4l2grab <v4l2grab-example>`.
-
-libv4l consists of 3 different libraries:
-
-
-libv4lconvert
-=============
-
-libv4lconvert is a library that converts several different pixelformats
-found in V4L2 drivers into a few common RGB and YUY formats.
-
-It currently accepts the following V4L2 driver formats:
-:ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>`,
-:ref:`V4L2_PIX_FMT_HM12 <V4L2-PIX-FMT-HM12>`,
-:ref:`V4L2_PIX_FMT_JPEG <V4L2-PIX-FMT-JPEG>`,
-:ref:`V4L2_PIX_FMT_MJPEG <V4L2-PIX-FMT-MJPEG>`,
-:ref:`V4L2_PIX_FMT_MR97310A <V4L2-PIX-FMT-MR97310A>`,
-:ref:`V4L2_PIX_FMT_OV511 <V4L2-PIX-FMT-OV511>`,
-:ref:`V4L2_PIX_FMT_OV518 <V4L2-PIX-FMT-OV518>`,
-:ref:`V4L2_PIX_FMT_PAC207 <V4L2-PIX-FMT-PAC207>`,
-:ref:`V4L2_PIX_FMT_PJPG <V4L2-PIX-FMT-PJPG>`,
-:ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>`,
-:ref:`V4L2_PIX_FMT_SBGGR8 <V4L2-PIX-FMT-SBGGR8>`,
-:ref:`V4L2_PIX_FMT_SGBRG8 <V4L2-PIX-FMT-SGBRG8>`,
-:ref:`V4L2_PIX_FMT_SGRBG8 <V4L2-PIX-FMT-SGRBG8>`,
-:ref:`V4L2_PIX_FMT_SN9C10X <V4L2-PIX-FMT-SN9C10X>`,
-:ref:`V4L2_PIX_FMT_SN9C20X_I420 <V4L2-PIX-FMT-SN9C20X-I420>`,
-:ref:`V4L2_PIX_FMT_SPCA501 <V4L2-PIX-FMT-SPCA501>`,
-:ref:`V4L2_PIX_FMT_SPCA505 <V4L2-PIX-FMT-SPCA505>`,
-:ref:`V4L2_PIX_FMT_SPCA508 <V4L2-PIX-FMT-SPCA508>`,
-:ref:`V4L2_PIX_FMT_SPCA561 <V4L2-PIX-FMT-SPCA561>`,
-:ref:`V4L2_PIX_FMT_SQ905C <V4L2-PIX-FMT-SQ905C>`,
-:ref:`V4L2_PIX_FMT_SRGGB8 <V4L2-PIX-FMT-SRGGB8>`,
-:ref:`V4L2_PIX_FMT_UYVY <V4L2-PIX-FMT-UYVY>`,
-:ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420>`,
-:ref:`V4L2_PIX_FMT_YUYV <V4L2-PIX-FMT-YUYV>`,
-:ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420>`, and
-:ref:`V4L2_PIX_FMT_YVYU <V4L2-PIX-FMT-YVYU>`.
-
-Later on libv4lconvert was expanded to also be able to do various video
-processing functions to improve webcam video quality. The video
-processing is split in to 2 parts: libv4lconvert/control and
-libv4lconvert/processing.
-
-The control part is used to offer video controls which can be used to
-control the video processing functions made available by
-libv4lconvert/processing. These controls are stored application wide
-(until reboot) by using a persistent shared memory object.
-
-libv4lconvert/processing offers the actual video processing
-functionality.
-
-
-libv4l1
-=======
-
-This library offers functions that can be used to quickly make v4l1
-applications work with v4l2 devices. These functions work exactly like
-the normal open/close/etc, except that libv4l1 does full emulation of
-the v4l1 api on top of v4l2 drivers, in case of v4l1 drivers it will
-just pass calls through.
-
-Since those functions are emulations of the old V4L1 API, it shouldn't
-be used for new applications.
-
-
-libv4l2
-=======
-
-This library should be used for all modern V4L2 applications.
-
-It provides handles to call V4L2 open/ioctl/close/poll methods. Instead
-of just providing the raw output of the device, it enhances the calls in
-the sense that it will use libv4lconvert to provide more video formats
-and to enhance the image quality.
-
-In most cases, libv4l2 just passes the calls directly through to the
-v4l2 driver, intercepting the calls to
-:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`,
-:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`,
-:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
-:ref:`VIDIOC_ENUM_FRAMESIZES <VIDIOC_ENUM_FRAMESIZES>` and
-:ref:`VIDIOC_ENUM_FRAMEINTERVALS <VIDIOC_ENUM_FRAMEINTERVALS>` in
-order to emulate the formats
-:ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>`,
-:ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>`,
-:ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420>`, and
-:ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420>`, if they aren't
-available in the driver. :ref:`VIDIOC_ENUM_FMT <VIDIOC_ENUM_FMT>`
-keeps enumerating the hardware supported formats, plus the emulated
-formats offered by libv4l at the end.
-
-
-.. _libv4l-ops:
-
-Libv4l device control functions
--------------------------------
-
-The common file operation methods are provided by libv4l.
-
-Those functions operate just like the gcc function ``dup()`` and
-V4L2 functions
-:c:func:`open() <v4l2-open>`, :c:func:`close() <v4l2-close>`,
-:c:func:`ioctl() <v4l2-ioctl>`, :c:func:`read() <v4l2-read>`,
-:c:func:`mmap() <v4l2-mmap>` and :c:func:`munmap() <v4l2-munmap>`:
-
-.. c:function:: int v4l2_open(const char *file, int oflag, ...)
-
- operates like the :c:func:`open() <v4l2-open>` function.
-
-.. c:function:: int v4l2_close(int fd)
-
- operates like the :c:func:`close() <v4l2-close>` function.
-
-.. c:function:: int v4l2_dup(int fd)
-
- operates like the libc ``dup()`` function, duplicating a file handler.
-
-.. c:function:: int v4l2_ioctl (int fd, unsigned long int request, ...)
-
- operates like the :c:func:`ioctl() <v4l2-ioctl>` function.
-
-.. c:function:: int v4l2_read (int fd, void* buffer, size_t n)
-
- operates like the :c:func:`read() <v4l2-read>` function.
-
-.. c:function:: void v4l2_mmap(void *start, size_t length, int prot, int flags, int fd, int64_t offset);
-
- operates like the :c:func:`munmap() <v4l2-munmap>` function.
-
-.. c:function:: int v4l2_munmap(void *_start, size_t length);
-
- operates like the :c:func:`munmap() <v4l2-munmap>` function.
-
-Those functions provide additional control:
-
-.. c:function:: int v4l2_fd_open(int fd, int v4l2_flags)
-
- opens an already opened fd for further use through v4l2lib and possibly
- modify libv4l2's default behavior through the ``v4l2_flags`` argument.
- Currently, ``v4l2_flags`` can be ``V4L2_DISABLE_CONVERSION``, to disable
- format conversion.
-
-.. c:function:: int v4l2_set_control(int fd, int cid, int value)
-
- This function takes a value of 0 - 65535, and then scales that range to the
- actual range of the given v4l control id, and then if the cid exists and is
- not locked sets the cid to the scaled value.
-
-.. c:function:: int v4l2_get_control(int fd, int cid)
-
- This function returns a value of 0 - 65535, scaled to from the actual range
- of the given v4l control id. when the cid does not exist, could not be
- accessed for some reason, or some error occurred 0 is returned.
-
-
-v4l1compat.so wrapper library
-=============================
-
-This library intercepts calls to
-:c:func:`open() <v4l2-open>`, :c:func:`close() <v4l2-close>`,
-:c:func:`ioctl() <v4l2-ioctl>`, :c:func:`mmap() <v4l2-mmap>` and
-:c:func:`munmap() <v4l2-munmap>`
-operations and redirects them to the libv4l counterparts, by using
-``LD_PRELOAD=/usr/lib/v4l1compat.so``. It also emulates V4L1 calls via V4L2
-API.
-
-It allows usage of binary legacy applications that still don't use
-libv4l.