1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _libv4l-introduction: 4 .. _libv4l-introduction:
5 5
6 ************ 6 ************
7 Introduction 7 Introduction
8 ************ 8 ************
9 9
10 libv4l is a collection of libraries which adds 10 libv4l is a collection of libraries which adds a thin abstraction layer
11 on top of video4linux2 devices. The purpose of 11 on top of video4linux2 devices. The purpose of this (thin) layer is to
12 make it easy for application writers to suppor 12 make it easy for application writers to support a wide variety of
13 devices without having to write separate code 13 devices without having to write separate code for different devices in
14 the same class. 14 the same class.
15 15
16 An example of using libv4l is provided by 16 An example of using libv4l is provided by
17 :ref:`v4l2grab <v4l2grab-example>`. 17 :ref:`v4l2grab <v4l2grab-example>`.
18 18
19 libv4l consists of 3 different libraries: 19 libv4l consists of 3 different libraries:
20 20
21 libv4lconvert 21 libv4lconvert
22 ============= 22 =============
23 23
24 libv4lconvert is a library that converts sever 24 libv4lconvert is a library that converts several different pixelformats
25 found in V4L2 drivers into a few common RGB an 25 found in V4L2 drivers into a few common RGB and YUY formats.
26 26
27 It currently accepts the following V4L2 driver 27 It currently accepts the following V4L2 driver formats:
28 :ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>` 28 :ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>`,
29 :ref:`V4L2_PIX_FMT_NV12_16L16 <V4L2-PIX-FMT-NV 29 :ref:`V4L2_PIX_FMT_NV12_16L16 <V4L2-PIX-FMT-NV12-16L16>`,
30 :ref:`V4L2_PIX_FMT_JPEG <V4L2-PIX-FMT-JPEG>`, 30 :ref:`V4L2_PIX_FMT_JPEG <V4L2-PIX-FMT-JPEG>`,
31 :ref:`V4L2_PIX_FMT_MJPEG <V4L2-PIX-FMT-MJPEG>` 31 :ref:`V4L2_PIX_FMT_MJPEG <V4L2-PIX-FMT-MJPEG>`,
32 :ref:`V4L2_PIX_FMT_MR97310A <V4L2-PIX-FMT-MR97 32 :ref:`V4L2_PIX_FMT_MR97310A <V4L2-PIX-FMT-MR97310A>`,
33 :ref:`V4L2_PIX_FMT_OV511 <V4L2-PIX-FMT-OV511>` 33 :ref:`V4L2_PIX_FMT_OV511 <V4L2-PIX-FMT-OV511>`,
34 :ref:`V4L2_PIX_FMT_OV518 <V4L2-PIX-FMT-OV518>` 34 :ref:`V4L2_PIX_FMT_OV518 <V4L2-PIX-FMT-OV518>`,
35 :ref:`V4L2_PIX_FMT_PAC207 <V4L2-PIX-FMT-PAC207 35 :ref:`V4L2_PIX_FMT_PAC207 <V4L2-PIX-FMT-PAC207>`,
36 :ref:`V4L2_PIX_FMT_PJPG <V4L2-PIX-FMT-PJPG>`, 36 :ref:`V4L2_PIX_FMT_PJPG <V4L2-PIX-FMT-PJPG>`,
37 :ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>` 37 :ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>`,
38 :ref:`V4L2_PIX_FMT_SBGGR8 <V4L2-PIX-FMT-SBGGR8 38 :ref:`V4L2_PIX_FMT_SBGGR8 <V4L2-PIX-FMT-SBGGR8>`,
39 :ref:`V4L2_PIX_FMT_SGBRG8 <V4L2-PIX-FMT-SGBRG8 39 :ref:`V4L2_PIX_FMT_SGBRG8 <V4L2-PIX-FMT-SGBRG8>`,
40 :ref:`V4L2_PIX_FMT_SGRBG8 <V4L2-PIX-FMT-SGRBG8 40 :ref:`V4L2_PIX_FMT_SGRBG8 <V4L2-PIX-FMT-SGRBG8>`,
41 :ref:`V4L2_PIX_FMT_SN9C10X <V4L2-PIX-FMT-SN9C1 41 :ref:`V4L2_PIX_FMT_SN9C10X <V4L2-PIX-FMT-SN9C10X>`,
42 :ref:`V4L2_PIX_FMT_SN9C20X_I420 <V4L2-PIX-FMT- 42 :ref:`V4L2_PIX_FMT_SN9C20X_I420 <V4L2-PIX-FMT-SN9C20X-I420>`,
43 :ref:`V4L2_PIX_FMT_SPCA501 <V4L2-PIX-FMT-SPCA5 43 :ref:`V4L2_PIX_FMT_SPCA501 <V4L2-PIX-FMT-SPCA501>`,
44 :ref:`V4L2_PIX_FMT_SPCA505 <V4L2-PIX-FMT-SPCA5 44 :ref:`V4L2_PIX_FMT_SPCA505 <V4L2-PIX-FMT-SPCA505>`,
45 :ref:`V4L2_PIX_FMT_SPCA508 <V4L2-PIX-FMT-SPCA5 45 :ref:`V4L2_PIX_FMT_SPCA508 <V4L2-PIX-FMT-SPCA508>`,
46 :ref:`V4L2_PIX_FMT_SPCA561 <V4L2-PIX-FMT-SPCA5 46 :ref:`V4L2_PIX_FMT_SPCA561 <V4L2-PIX-FMT-SPCA561>`,
47 :ref:`V4L2_PIX_FMT_SQ905C <V4L2-PIX-FMT-SQ905C 47 :ref:`V4L2_PIX_FMT_SQ905C <V4L2-PIX-FMT-SQ905C>`,
48 :ref:`V4L2_PIX_FMT_SRGGB8 <V4L2-PIX-FMT-SRGGB8 48 :ref:`V4L2_PIX_FMT_SRGGB8 <V4L2-PIX-FMT-SRGGB8>`,
49 :ref:`V4L2_PIX_FMT_UYVY <V4L2-PIX-FMT-UYVY>`, 49 :ref:`V4L2_PIX_FMT_UYVY <V4L2-PIX-FMT-UYVY>`,
50 :ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420 50 :ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420>`,
51 :ref:`V4L2_PIX_FMT_YUYV <V4L2-PIX-FMT-YUYV>`, 51 :ref:`V4L2_PIX_FMT_YUYV <V4L2-PIX-FMT-YUYV>`,
52 :ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420 52 :ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420>`, and
53 :ref:`V4L2_PIX_FMT_YVYU <V4L2-PIX-FMT-YVYU>`. 53 :ref:`V4L2_PIX_FMT_YVYU <V4L2-PIX-FMT-YVYU>`.
54 54
55 Later on libv4lconvert was expanded to also be 55 Later on libv4lconvert was expanded to also be able to do various video
56 processing functions to improve webcam video q 56 processing functions to improve webcam video quality. The video
57 processing is split in to 2 parts: libv4lconve 57 processing is split in to 2 parts: libv4lconvert/control and
58 libv4lconvert/processing. 58 libv4lconvert/processing.
59 59
60 The control part is used to offer video contro 60 The control part is used to offer video controls which can be used to
61 control the video processing functions made av 61 control the video processing functions made available by
62 libv4lconvert/processing. These controls are s 62 libv4lconvert/processing. These controls are stored application wide
63 (until reboot) by using a persistent shared me 63 (until reboot) by using a persistent shared memory object.
64 64
65 libv4lconvert/processing offers the actual vid 65 libv4lconvert/processing offers the actual video processing
66 functionality. 66 functionality.
67 67
68 libv4l1 68 libv4l1
69 ======= 69 =======
70 70
71 This library offers functions that can be used 71 This library offers functions that can be used to quickly make v4l1
72 applications work with v4l2 devices. These fun 72 applications work with v4l2 devices. These functions work exactly like
73 the normal open/close/etc, except that libv4l1 73 the normal open/close/etc, except that libv4l1 does full emulation of
74 the v4l1 api on top of v4l2 drivers, in case o 74 the v4l1 api on top of v4l2 drivers, in case of v4l1 drivers it will
75 just pass calls through. 75 just pass calls through.
76 76
77 Since those functions are emulations of the ol 77 Since those functions are emulations of the old V4L1 API, it shouldn't
78 be used for new applications. 78 be used for new applications.
79 79
80 libv4l2 80 libv4l2
81 ======= 81 =======
82 82
83 This library should be used for all modern V4L 83 This library should be used for all modern V4L2 applications.
84 84
85 It provides handles to call V4L2 open/ioctl/cl 85 It provides handles to call V4L2 open/ioctl/close/poll methods. Instead
86 of just providing the raw output of the device 86 of just providing the raw output of the device, it enhances the calls in
87 the sense that it will use libv4lconvert to pr 87 the sense that it will use libv4lconvert to provide more video formats
88 and to enhance the image quality. 88 and to enhance the image quality.
89 89
90 In most cases, libv4l2 just passes the calls d 90 In most cases, libv4l2 just passes the calls directly through to the
91 v4l2 driver, intercepting the calls to 91 v4l2 driver, intercepting the calls to
92 :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`, 92 :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`,
93 :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, 93 :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`,
94 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, 94 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
95 :ref:`VIDIOC_ENUM_FRAMESIZES <VIDIOC_ENUM_FRAM 95 :ref:`VIDIOC_ENUM_FRAMESIZES <VIDIOC_ENUM_FRAMESIZES>` and
96 :ref:`VIDIOC_ENUM_FRAMEINTERVALS <VIDIOC_ENUM_ 96 :ref:`VIDIOC_ENUM_FRAMEINTERVALS <VIDIOC_ENUM_FRAMEINTERVALS>` in
97 order to emulate the formats 97 order to emulate the formats
98 :ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>` 98 :ref:`V4L2_PIX_FMT_BGR24 <V4L2-PIX-FMT-BGR24>`,
99 :ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>` 99 :ref:`V4L2_PIX_FMT_RGB24 <V4L2-PIX-FMT-RGB24>`,
100 :ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420 100 :ref:`V4L2_PIX_FMT_YUV420 <V4L2-PIX-FMT-YUV420>`, and
101 :ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420 101 :ref:`V4L2_PIX_FMT_YVU420 <V4L2-PIX-FMT-YVU420>`, if they aren't
102 available in the driver. :ref:`VIDIOC_ENUM_FMT 102 available in the driver. :ref:`VIDIOC_ENUM_FMT <VIDIOC_ENUM_FMT>`
103 keeps enumerating the hardware supported forma 103 keeps enumerating the hardware supported formats, plus the emulated
104 formats offered by libv4l at the end. 104 formats offered by libv4l at the end.
105 105
106 .. _libv4l-ops: 106 .. _libv4l-ops:
107 107
108 Libv4l device control functions 108 Libv4l device control functions
109 ------------------------------- 109 -------------------------------
110 110
111 The common file operation methods are provided 111 The common file operation methods are provided by libv4l.
112 112
113 Those functions operate just like the gcc func 113 Those functions operate just like the gcc function ``dup()`` and
114 V4L2 functions 114 V4L2 functions
115 :c:func:`open()`, :c:func:`close()`, 115 :c:func:`open()`, :c:func:`close()`,
116 :c:func:`ioctl()`, :c:func:`read()`, 116 :c:func:`ioctl()`, :c:func:`read()`,
117 :c:func:`mmap()` and :c:func:`munmap()`: 117 :c:func:`mmap()` and :c:func:`munmap()`:
118 118
119 .. c:function:: int v4l2_open(const char *file 119 .. c:function:: int v4l2_open(const char *file, int oflag, ...)
120 120
121 operates like the :c:func:`open()` function 121 operates like the :c:func:`open()` function.
122 122
123 .. c:function:: int v4l2_close(int fd) 123 .. c:function:: int v4l2_close(int fd)
124 124
125 operates like the :c:func:`close()` functio 125 operates like the :c:func:`close()` function.
126 126
127 .. c:function:: int v4l2_dup(int fd) 127 .. c:function:: int v4l2_dup(int fd)
128 128
129 operates like the libc ``dup()`` function, 129 operates like the libc ``dup()`` function, duplicating a file handler.
130 130
131 .. c:function:: int v4l2_ioctl (int fd, unsign 131 .. c:function:: int v4l2_ioctl (int fd, unsigned long int request, ...)
132 132
133 operates like the :c:func:`ioctl()` functio 133 operates like the :c:func:`ioctl()` function.
134 134
135 .. c:function:: int v4l2_read (int fd, void* b 135 .. c:function:: int v4l2_read (int fd, void* buffer, size_t n)
136 136
137 operates like the :c:func:`read()` function 137 operates like the :c:func:`read()` function.
138 138
139 .. c:function:: void *v4l2_mmap(void *start, s 139 .. c:function:: void *v4l2_mmap(void *start, size_t length, int prot, int flags, int fd, int64_t offset);
140 140
141 operates like the :c:func:`mmap()` function 141 operates like the :c:func:`mmap()` function.
142 142
143 .. c:function:: int v4l2_munmap(void *_start, 143 .. c:function:: int v4l2_munmap(void *_start, size_t length);
144 144
145 operates like the :c:func:`munmap()` functi 145 operates like the :c:func:`munmap()` function.
146 146
147 Those functions provide additional control: 147 Those functions provide additional control:
148 148
149 .. c:function:: int v4l2_fd_open(int fd, int v 149 .. c:function:: int v4l2_fd_open(int fd, int v4l2_flags)
150 150
151 opens an already opened fd for further use 151 opens an already opened fd for further use through v4l2lib and possibly
152 modify libv4l2's default behavior through t 152 modify libv4l2's default behavior through the ``v4l2_flags`` argument.
153 Currently, ``v4l2_flags`` can be ``V4L2_DIS 153 Currently, ``v4l2_flags`` can be ``V4L2_DISABLE_CONVERSION``, to disable
154 format conversion. 154 format conversion.
155 155
156 .. c:function:: int v4l2_set_control(int fd, i 156 .. c:function:: int v4l2_set_control(int fd, int cid, int value)
157 157
158 This function takes a value of 0 - 65535, a 158 This function takes a value of 0 - 65535, and then scales that range to the
159 actual range of the given v4l control id, a 159 actual range of the given v4l control id, and then if the cid exists and is
160 not locked sets the cid to the scaled value 160 not locked sets the cid to the scaled value.
161 161
162 .. c:function:: int v4l2_get_control(int fd, i 162 .. c:function:: int v4l2_get_control(int fd, int cid)
163 163
164 This function returns a value of 0 - 65535, 164 This function returns a value of 0 - 65535, scaled to from the actual range
165 of the given v4l control id. when the cid d 165 of the given v4l control id. when the cid does not exist, could not be
166 accessed for some reason, or some error occ 166 accessed for some reason, or some error occurred 0 is returned.
167 167
168 v4l1compat.so wrapper library 168 v4l1compat.so wrapper library
169 ============================= 169 =============================
170 170
171 This library intercepts calls to 171 This library intercepts calls to
172 :c:func:`open()`, :c:func:`close()`, 172 :c:func:`open()`, :c:func:`close()`,
173 :c:func:`ioctl()`, :c:func:`mmap()` and 173 :c:func:`ioctl()`, :c:func:`mmap()` and
174 :c:func:`munmap()` 174 :c:func:`munmap()`
175 operations and redirects them to the libv4l co 175 operations and redirects them to the libv4l counterparts, by using
176 ``LD_PRELOAD=/usr/lib/v4l1compat.so``. It also 176 ``LD_PRELOAD=/usr/lib/v4l1compat.so``. It also emulates V4L1 calls via V4L2
177 API. 177 API.
178 178
179 It allows usage of binary legacy applications 179 It allows usage of binary legacy applications that still don't use
180 libv4l. 180 libv4l.
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