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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 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_G_FMT, struct v4l2_format *argp ) |
19 | :name: VIDIOC_G_FMT | |
5377d91f | 20 | |
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21 | .. c:function:: int ioctl( int fd, VIDIOC_S_FMT, struct v4l2_format *argp ) |
22 | :name: VIDIOC_S_FMT | |
23 | ||
24 | .. c:function:: int ioctl( int fd, VIDIOC_TRY_FMT, struct v4l2_format *argp ) | |
25 | :name: VIDIOC_TRY_FMT | |
586027ce | 26 | |
15e7d615 | 27 | Arguments |
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28 | ========= |
29 | ||
30 | ``fd`` | |
31 | File descriptor returned by :ref:`open() <func-open>`. | |
32 | ||
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33 | ``argp`` |
34 | ||
35 | ||
15e7d615 | 36 | Description |
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37 | =========== |
38 | ||
39 | These ioctls are used to negotiate the format of data (typically image | |
40 | format) exchanged between driver and application. | |
41 | ||
42 | To query the current parameters applications set the ``type`` field of a | |
fc78c7c7 | 43 | struct :c:type:`v4l2_format` to the respective buffer (stream) |
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44 | type. For example video capture devices use |
45 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or | |
46 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the | |
4e03cb76 | 47 | :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills |
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48 | the respective member of the ``fmt`` union. In case of video capture |
49 | devices that is either the struct | |
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50 | :c:type:`v4l2_pix_format` ``pix`` or the struct |
51 | :c:type:`v4l2_pix_format_mplane` ``pix_mp`` | |
5377d91f | 52 | member. When the requested buffer type is not supported drivers return |
cdb4af0f | 53 | an ``EINVAL`` error code. |
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54 | |
55 | To change the current format parameters applications initialize the | |
56 | ``type`` field and all fields of the respective ``fmt`` union member. | |
57 | For details see the documentation of the various devices types in | |
58 | :ref:`devices`. Good practice is to query the current parameters | |
59 | first, and to modify only those parameters not suitable for the | |
2212ff25 | 60 | application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
fc78c7c7 | 61 | a pointer to a struct :c:type:`v4l2_format` structure the driver |
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62 | checks and adjusts the parameters against hardware abilities. Drivers |
63 | should not return an error code unless the ``type`` field is invalid, | |
64 | this is a mechanism to fathom device capabilities and to approach | |
65 | parameters acceptable for both the application and driver. On success | |
66 | the driver may program the hardware, allocate resources and generally | |
2212ff25 | 67 | prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns |
4e03cb76 | 68 | the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple, |
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69 | inflexible devices may even ignore all input and always return the |
70 | default parameters. However all V4L2 devices exchanging data with the | |
4e03cb76 | 71 | application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` |
5377d91f | 72 | ioctl. When the requested buffer type is not supported drivers return an |
2212ff25 | 73 | EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in |
5377d91f | 74 | progress or the resource is not available for other reasons drivers |
cdb4af0f | 75 | return the ``EBUSY`` error code. |
5377d91f | 76 | |
2212ff25 | 77 | The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one |
5377d91f | 78 | exception: it does not change driver state. It can also be called at any |
cdb4af0f | 79 | time, never returning ``EBUSY``. This function is provided to negotiate |
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80 | parameters, to learn about hardware limitations, without disabling I/O |
81 | or possibly time consuming hardware preparations. Although strongly | |
82 | recommended drivers are not required to implement this ioctl. | |
83 | ||
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84 | The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what |
85 | :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output. | |
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86 | |
87 | ||
e8be7e97 | 88 | .. c:type:: v4l2_format |
5377d91f | 89 | |
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90 | .. tabularcolumns:: |p{1.2cm}|p{4.3cm}|p{3.0cm}|p{9.0cm}| |
91 | ||
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92 | .. flat-table:: struct v4l2_format |
93 | :header-rows: 0 | |
94 | :stub-columns: 0 | |
95 | ||
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96 | * - __u32 |
97 | - ``type`` | |
98 | - | |
99 | - Type of the data stream, see :c:type:`v4l2_buf_type`. | |
100 | * - union | |
101 | - ``fmt`` | |
102 | * - | |
103 | - struct :c:type:`v4l2_pix_format` | |
104 | - ``pix`` | |
105 | - Definition of an image format, see :ref:`pixfmt`, used by video | |
106 | capture and output devices. | |
107 | * - | |
108 | - struct :c:type:`v4l2_pix_format_mplane` | |
109 | - ``pix_mp`` | |
110 | - Definition of an image format, see :ref:`pixfmt`, used by video | |
111 | capture and output devices that support the | |
112 | :ref:`multi-planar version of the API <planar-apis>`. | |
113 | * - | |
114 | - struct :c:type:`v4l2_window` | |
115 | - ``win`` | |
116 | - Definition of an overlaid image, see :ref:`overlay`, used by | |
117 | video overlay devices. | |
118 | * - | |
119 | - struct :c:type:`v4l2_vbi_format` | |
120 | - ``vbi`` | |
121 | - Raw VBI capture or output parameters. This is discussed in more | |
122 | detail in :ref:`raw-vbi`. Used by raw VBI capture and output | |
123 | devices. | |
124 | * - | |
125 | - struct :c:type:`v4l2_sliced_vbi_format` | |
126 | - ``sliced`` | |
127 | - Sliced VBI capture or output parameters. See :ref:`sliced` for | |
128 | details. Used by sliced VBI capture and output devices. | |
129 | * - | |
130 | - struct :c:type:`v4l2_sdr_format` | |
131 | - ``sdr`` | |
132 | - Definition of a data format, see :ref:`pixfmt`, used by SDR | |
133 | capture and output devices. | |
134 | * - | |
135 | - __u8 | |
136 | - ``raw_data``\ [200] | |
137 | - Place holder for future extensions. | |
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138 | |
139 | ||
15e7d615 | 140 | Return Value |
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141 | ============ |
142 | ||
143 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
144 | appropriately. The generic error codes are described at the | |
145 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
146 | ||
147 | EINVAL | |
e8be7e97 | 148 | The struct :c:type:`v4l2_format` ``type`` field is |
5377d91f | 149 | invalid or the requested buffer type not supported. |
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150 | |
151 | EBUSY | |
152 | The device is busy and cannot change the format. This could be | |
153 | because or the device is streaming or buffers are allocated or | |
154 | queued to the driver. Relevant for :ref:`VIDIOC_S_FMT | |
155 | <VIDIOC_G_FMT>` only. |