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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_G_FMT: |
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4 | |
5 | ************************************************ | |
6 | ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT | |
7 | ************************************************ | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
b7e67f6c | 18 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_format *argp ) |
5377d91f | 19 | |
586027ce | 20 | |
15e7d615 | 21 | Arguments |
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22 | ========= |
23 | ||
24 | ``fd`` | |
25 | File descriptor returned by :ref:`open() <func-open>`. | |
26 | ||
27 | ``request`` | |
28 | VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT | |
29 | ||
30 | ``argp`` | |
31 | ||
32 | ||
15e7d615 | 33 | Description |
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34 | =========== |
35 | ||
36 | These ioctls are used to negotiate the format of data (typically image | |
37 | format) exchanged between driver and application. | |
38 | ||
39 | To query the current parameters applications set the ``type`` field of a | |
acf309a2 | 40 | struct :ref:`struct v4l2_format <v4l2-format>` to the respective buffer (stream) |
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41 | type. For example video capture devices use |
42 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or | |
43 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the | |
4e03cb76 | 44 | :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills |
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45 | the respective member of the ``fmt`` union. In case of video capture |
46 | devices that is either the struct | |
47 | :ref:`v4l2_pix_format <v4l2-pix-format>` ``pix`` or the struct | |
48 | :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` ``pix_mp`` | |
49 | member. When the requested buffer type is not supported drivers return | |
cdb4af0f | 50 | an ``EINVAL`` error code. |
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51 | |
52 | To change the current format parameters applications initialize the | |
53 | ``type`` field and all fields of the respective ``fmt`` union member. | |
54 | For details see the documentation of the various devices types in | |
55 | :ref:`devices`. Good practice is to query the current parameters | |
56 | first, and to modify only those parameters not suitable for the | |
2212ff25 | 57 | application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
acf309a2 | 58 | a pointer to a :ref:`struct v4l2_format <v4l2-format>` structure the driver |
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59 | checks and adjusts the parameters against hardware abilities. Drivers |
60 | should not return an error code unless the ``type`` field is invalid, | |
61 | this is a mechanism to fathom device capabilities and to approach | |
62 | parameters acceptable for both the application and driver. On success | |
63 | the driver may program the hardware, allocate resources and generally | |
2212ff25 | 64 | prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns |
4e03cb76 | 65 | the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple, |
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66 | inflexible devices may even ignore all input and always return the |
67 | default parameters. However all V4L2 devices exchanging data with the | |
4e03cb76 | 68 | application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` |
5377d91f | 69 | ioctl. When the requested buffer type is not supported drivers return an |
2212ff25 | 70 | EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in |
5377d91f | 71 | progress or the resource is not available for other reasons drivers |
cdb4af0f | 72 | return the ``EBUSY`` error code. |
5377d91f | 73 | |
2212ff25 | 74 | The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one |
5377d91f | 75 | exception: it does not change driver state. It can also be called at any |
cdb4af0f | 76 | time, never returning ``EBUSY``. This function is provided to negotiate |
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77 | parameters, to learn about hardware limitations, without disabling I/O |
78 | or possibly time consuming hardware preparations. Although strongly | |
79 | recommended drivers are not required to implement this ioctl. | |
80 | ||
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81 | The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what |
82 | :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output. | |
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83 | |
84 | ||
85 | .. _v4l2-format: | |
86 | ||
87 | .. flat-table:: struct v4l2_format | |
88 | :header-rows: 0 | |
89 | :stub-columns: 0 | |
90 | ||
91 | ||
92 | - .. row 1 | |
93 | ||
94 | - __u32 | |
95 | ||
96 | - ``type`` | |
97 | ||
0579e6e3 | 98 | - |
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99 | - Type of the data stream, see :ref:`v4l2-buf-type`. |
100 | ||
101 | - .. row 2 | |
102 | ||
103 | - union | |
104 | ||
105 | - ``fmt`` | |
106 | ||
107 | - .. row 3 | |
108 | ||
0579e6e3 | 109 | - |
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110 | - struct :ref:`v4l2_pix_format <v4l2-pix-format>` |
111 | ||
112 | - ``pix`` | |
113 | ||
114 | - Definition of an image format, see :ref:`pixfmt`, used by video | |
0579e6e3 | 115 | capture and output devices. |
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116 | |
117 | - .. row 4 | |
118 | ||
0579e6e3 | 119 | - |
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120 | - struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` |
121 | ||
122 | - ``pix_mp`` | |
123 | ||
124 | - Definition of an image format, see :ref:`pixfmt`, used by video | |
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125 | capture and output devices that support the |
126 | :ref:`multi-planar version of the API <planar-apis>`. | |
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127 | |
128 | - .. row 5 | |
129 | ||
0579e6e3 | 130 | - |
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131 | - struct :ref:`v4l2_window <v4l2-window>` |
132 | ||
133 | - ``win`` | |
134 | ||
135 | - Definition of an overlaid image, see :ref:`overlay`, used by | |
0579e6e3 | 136 | video overlay devices. |
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137 | |
138 | - .. row 6 | |
139 | ||
0579e6e3 | 140 | - |
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141 | - struct :ref:`v4l2_vbi_format <v4l2-vbi-format>` |
142 | ||
143 | - ``vbi`` | |
144 | ||
145 | - Raw VBI capture or output parameters. This is discussed in more | |
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146 | detail in :ref:`raw-vbi`. Used by raw VBI capture and output |
147 | devices. | |
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148 | |
149 | - .. row 7 | |
150 | ||
0579e6e3 | 151 | - |
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152 | - struct :ref:`v4l2_sliced_vbi_format <v4l2-sliced-vbi-format>` |
153 | ||
154 | - ``sliced`` | |
155 | ||
156 | - Sliced VBI capture or output parameters. See :ref:`sliced` for | |
0579e6e3 | 157 | details. Used by sliced VBI capture and output devices. |
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158 | |
159 | - .. row 8 | |
160 | ||
0579e6e3 | 161 | - |
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162 | - struct :ref:`v4l2_sdr_format <v4l2-sdr-format>` |
163 | ||
164 | - ``sdr`` | |
165 | ||
166 | - Definition of a data format, see :ref:`pixfmt`, used by SDR | |
0579e6e3 | 167 | capture and output devices. |
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168 | |
169 | - .. row 9 | |
170 | ||
0579e6e3 | 171 | - |
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172 | - __u8 |
173 | ||
8968da9b | 174 | - ``raw_data``\ [200] |
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175 | |
176 | - Place holder for future extensions. | |
177 | ||
178 | ||
15e7d615 | 179 | Return Value |
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180 | ============ |
181 | ||
182 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
183 | appropriately. The generic error codes are described at the | |
184 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
185 | ||
186 | EINVAL | |
187 | The struct :ref:`v4l2_format <v4l2-format>` ``type`` field is | |
188 | invalid or the requested buffer type not supported. |