media/v4l/dev-raw-vbi.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
4 .. _raw-vbi:
19 signal, or to be added to a signal for output. The data format is
55 Raw VBI Format Negotiation
106 .. flat-table:: struct v4l2_vbi_format
107     :header-rows:  0
108     :stub-columns: 0
111     * - __u32
112       - ``sampling_rate``
113       - Samples per second, i. e. unit 1 Hz.
114     * - __u32
115       - ``offset``
116       - Horizontal offset of the VBI image, relative to the leading edge
118 	first sample in the VBI image will be located ``offset`` /
120 	:ref:`vbi-hsync`.
121     * - __u32
122       - ``samples_per_line``
123       -
124     * - __u32
125       - ``sample_format``
126       - Defines the sample format as in :ref:`pixfmt`, a
127 	four-character-code. [#f2]_ Usually this is ``V4L2_PIX_FMT_GREY``,
128 	i. e. each sample consists of 8 bits with lower values oriented
132 	may not be the mean value of the signal. Drivers shall not convert
133 	the sample format by software.
134     * - __u32
135       - ``start``\ [#f2]_
136       - This is the scanning system line number associated with the first
138 	respectively. See :ref:`vbi-525` and :ref:`vbi-625` for valid
142 	for each field for each 525 or 625 line format as a convenience.
147     * - __u32
148       - ``count``\ [#f2]_
149       - The number of lines in the first and second field image,
151     * - :cspan:`2`
163 	return both count values non-zero.
171 	:ref:`v4l2_std_id <v4l2-std-id>` or the ``framelines`` field
174     * - __u32
175       - ``flags``
176       - See :ref:`vbifmt-flags` below. Currently only drivers set flags,
178     * - __u32
179       - ``reserved``\ [#f2]_
180       - This array is reserved for future extensions. Drivers and
185 .. _vbifmt-flags:
187 .. flat-table:: Raw VBI Format Flags
188     :header-rows:  0
189     :stub-columns: 0
192     * - ``V4L2_VBI_UNSYNC``
193       - 0x0001
194       - This flag indicates hardware which does not properly distinguish
201     * - ``V4L2_VBI_INTERLACED``
202       - 0x0002
203       - By default the two field images will be passed sequentially; all
205 	(compare :ref:`field-order` ``V4L2_FIELD_SEQ_TB`` and
215 	non-zero.
218 .. _vbi-hsync:
220 .. kernel-figure:: vbi_hsync.svg
226 .. _vbi-525:
228 .. kernel-figure:: vbi_525.svg
232     **Figure 4.2. ITU-R 525 line numbering (M/NTSC and M/PAL)**
234 .. _vbi-625:
236 .. kernel-figure:: vbi_625.svg
240     **Figure 4.3. ITU-R 625 line numbering**
242 Remember the VBI image format depends on the selected video standard,
244 current standard first. Attempts to read or write data ahead of format
246 the negotiated VBI parameters, should be refused by the driver. A format
258 .. code-block:: c
260     (count[0] + count[1]) * samples_per_line * sample size in bytes
262 The sample size is most likely always one byte, applications must check
279    ASK: Amplitude-Shift Keying. A high signal level represents a '1'
283    A few devices may be unable to sample VBI data at all but can extend
292    The valid values ar shown at :ref:`vbi-525` and :ref:`vbi-625`.