1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_ENUM_FMT:
5
6*********************
7ioctl VIDIOC_ENUM_FMT
8*********************
9
10Name
11====
12
13VIDIOC_ENUM_FMT - Enumerate image formats
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_ENUM_FMT
19
20``int ioctl(int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp)``
21
22Arguments
23=========
24
25``fd``
26    File descriptor returned by :c:func:`open()`.
27
28``argp``
29    Pointer to struct :c:type:`v4l2_fmtdesc`.
30
31Description
32===========
33
34To enumerate image formats applications initialize the ``type``, ``mbus_code``
35and ``index`` fields of struct :c:type:`v4l2_fmtdesc` and call
36the :ref:`VIDIOC_ENUM_FMT` ioctl with a pointer to this structure. Drivers
37fill the rest of the structure or return an ``EINVAL`` error code. All
38formats are enumerable by beginning at index zero and incrementing by
39one until ``EINVAL`` is returned. If applicable, drivers shall return
40formats in preference order, where preferred formats are returned before
41(that is, with lower ``index`` value) less-preferred formats.
42
43Depending on the ``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`,
44the ``mbus_code`` field is handled differently:
45
461) ``V4L2_CAP_IO_MC`` is not set (also known as a 'video-node-centric' driver)
47
48   Applications shall initialize the ``mbus_code`` field to zero and drivers
49   shall ignore the value of the field.
50
51   Drivers shall enumerate all image formats.
52
53   .. note::
54
55      After switching the input or output the list of enumerated image
56      formats may be different.
57
582) ``V4L2_CAP_IO_MC`` is set (also known as an 'MC-centric' driver)
59
60   If the ``mbus_code`` field is zero, then all image formats
61   shall be enumerated.
62
63   If the ``mbus_code`` field is initialized to a valid (non-zero)
64   :ref:`media bus format code <v4l2-mbus-pixelcode>`, then drivers
65   shall restrict enumeration to only the image formats that can produce
66   (for video output devices) or be produced from (for video capture
67   devices) that media bus code. If the ``mbus_code`` is unsupported by
68   the driver, then ``EINVAL`` shall be returned.
69
70   Regardless of the value of the ``mbus_code`` field, the enumerated image
71   formats shall not depend on the active configuration of the video device
72   or device pipeline.
73
74.. c:type:: v4l2_fmtdesc
75
76.. cssclass:: longtable
77
78.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
79
80.. flat-table:: struct v4l2_fmtdesc
81    :header-rows:  0
82    :stub-columns: 0
83    :widths:       1 1 2
84
85    * - __u32
86      - ``index``
87      - Number of the format in the enumeration, set by the application.
88	This is in no way related to the ``pixelformat`` field.
89    * - __u32
90      - ``type``
91      - Type of the data stream, set by the application. Only these types
92	are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``,
93	``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
94	``V4L2_BUF_TYPE_VIDEO_OUTPUT``,
95	``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``,
96	``V4L2_BUF_TYPE_VIDEO_OVERLAY``,
97	``V4L2_BUF_TYPE_SDR_CAPTURE``,
98	``V4L2_BUF_TYPE_SDR_OUTPUT``,
99	``V4L2_BUF_TYPE_META_CAPTURE`` and
100	``V4L2_BUF_TYPE_META_OUTPUT``.
101	See :c:type:`v4l2_buf_type`.
102    * - __u32
103      - ``flags``
104      - See :ref:`fmtdesc-flags`
105    * - __u8
106      - ``description``\ [32]
107      - Description of the format, a NUL-terminated ASCII string. This
108	information is intended for the user, for example: "YUV 4:2:2".
109    * - __u32
110      - ``pixelformat``
111      - The image format identifier. This is a four character code as
112	computed by the v4l2_fourcc() macro:
113    * - :cspan:`2`
114
115	.. _v4l2-fourcc:
116
117	``#define v4l2_fourcc(a,b,c,d)``
118
119	``(((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))``
120
121	Several image formats are already defined by this specification in
122	:ref:`pixfmt`.
123
124	.. attention::
125
126	   These codes are not the same as those used
127	   in the Windows world.
128    * - __u32
129      - ``mbus_code``
130      - Media bus code restricting the enumerated formats, set by the
131        application. Only applicable to drivers that advertise the
132        ``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`, shall be 0
133        otherwise.
134    * - __u32
135      - ``reserved``\ [3]
136      - Reserved for future extensions. Drivers must set the array to
137	zero.
138
139
140.. tabularcolumns:: |p{8.4cm}|p{1.8cm}|p{7.1cm}|
141
142.. cssclass:: longtable
143
144.. _fmtdesc-flags:
145
146.. flat-table:: Image Format Description Flags
147    :header-rows:  0
148    :stub-columns: 0
149    :widths:       3 1 4
150
151    * - ``V4L2_FMT_FLAG_COMPRESSED``
152      - 0x0001
153      - This is a compressed format.
154    * - ``V4L2_FMT_FLAG_EMULATED``
155      - 0x0002
156      - This format is not native to the device but emulated through
157	software (usually libv4l2), where possible try to use a native
158	format instead for better performance.
159    * - ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
160      - 0x0004
161      - The hardware decoder for this compressed bytestream format (aka coded
162	format) is capable of parsing a continuous bytestream. Applications do
163	not need to parse the bytestream themselves to find the boundaries
164	between frames/fields.
165
166	This flag can only be used in combination with the
167	``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to compressed
168	formats only. This flag is valid for stateful decoders only.
169    * - ``V4L2_FMT_FLAG_DYN_RESOLUTION``
170      - 0x0008
171      - Dynamic resolution switching is supported by the device for this
172	compressed bytestream format (aka coded format). It will notify the user
173	via the event ``V4L2_EVENT_SOURCE_CHANGE`` when changes in the video
174	parameters are detected.
175
176	This flag can only be used in combination with the
177	``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to
178	compressed formats only. This flag is valid for stateful codecs only.
179    * - ``V4L2_FMT_FLAG_ENC_CAP_FRAME_INTERVAL``
180      - 0x0010
181      - The hardware encoder supports setting the ``CAPTURE`` coded frame
182	interval separately from the ``OUTPUT`` raw frame interval.
183	Setting the ``OUTPUT`` raw frame interval with :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>`
184	also sets the ``CAPTURE`` coded frame interval to the same value.
185	If this flag is set, then the ``CAPTURE`` coded frame interval can be
186	set to a different value afterwards. This is typically used for
187	offline encoding where the ``OUTPUT`` raw frame interval is used as
188	a hint for reserving hardware encoder resources and the ``CAPTURE`` coded
189	frame interval is the actual frame rate embedded in the encoded video
190	stream.
191
192	This flag can only be used in combination with the
193	``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to
194        compressed formats only. This flag is valid for stateful encoders only.
195    * - ``V4L2_FMT_FLAG_CSC_COLORSPACE``
196      - 0x0020
197      - The driver allows the application to try to change the default
198	colorspace. This flag is relevant only for capture devices.
199	The application can ask to configure the colorspace of the capture device
200	when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
201	:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
202    * - ``V4L2_FMT_FLAG_CSC_XFER_FUNC``
203      - 0x0040
204      - The driver allows the application to try to change the default
205	transfer function. This flag is relevant only for capture devices.
206	The application can ask to configure the transfer function of the capture
207	device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
208	:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
209    * - ``V4L2_FMT_FLAG_CSC_YCBCR_ENC``
210      - 0x0080
211      - The driver allows the application to try to change the default
212	Y'CbCr encoding. This flag is relevant only for capture devices.
213	The application can ask to configure the Y'CbCr encoding of the capture device
214	when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
215	:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
216    * - ``V4L2_FMT_FLAG_CSC_HSV_ENC``
217      - 0x0080
218      - The driver allows the application to try to change the default
219	HSV encoding. This flag is relevant only for capture devices.
220	The application can ask to configure the HSV encoding of the capture device
221	when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
222	:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
223    * - ``V4L2_FMT_FLAG_CSC_QUANTIZATION``
224      - 0x0100
225      - The driver allows the application to try to change the default
226	quantization. This flag is relevant only for capture devices.
227	The application can ask to configure the quantization of the capture
228	device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
229	:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
230
231Return Value
232============
233
234On success 0 is returned, on error -1 and the ``errno`` variable is set
235appropriately. The generic error codes are described at the
236:ref:`Generic Error Codes <gen-errors>` chapter.
237
238EINVAL
239    The struct :c:type:`v4l2_fmtdesc` ``type`` is not
240    supported or the ``index`` is out of bounds.
241
242    If ``V4L2_CAP_IO_MC`` is set and the specified ``mbus_code``
243    is unsupported, then also return this error code.
244