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Diffstat (limited to 'Documentation/media/uapi/v4l/dev-raw-vbi.rst')
| -rw-r--r-- | Documentation/media/uapi/v4l/dev-raw-vbi.rst | 243 |
1 files changed, 95 insertions, 148 deletions
diff --git a/Documentation/media/uapi/v4l/dev-raw-vbi.rst b/Documentation/media/uapi/v4l/dev-raw-vbi.rst index 26ec24a94103..b82d837e4ff1 100644 --- a/Documentation/media/uapi/v4l/dev-raw-vbi.rst +++ b/Documentation/media/uapi/v4l/dev-raw-vbi.rst @@ -110,120 +110,77 @@ and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does :stub-columns: 0 :widths: 1 1 2 - - - .. row 1 - - - __u32 - - - ``sampling_rate`` - - - Samples per second, i. e. unit 1 Hz. - - - .. row 2 - - - __u32 - - - ``offset`` - - - Horizontal offset of the VBI image, relative to the leading edge - of the line synchronization pulse and counted in samples: The - first sample in the VBI image will be located ``offset`` / - ``sampling_rate`` seconds following the leading edge. See also - :ref:`vbi-hsync`. - - - .. row 3 - - - __u32 - - - ``samples_per_line`` - - - - - - .. row 4 - - - __u32 - - - ``sample_format`` - - - Defines the sample format as in :ref:`pixfmt`, a - four-character-code. [#f2]_ Usually this is ``V4L2_PIX_FMT_GREY``, - i. e. each sample consists of 8 bits with lower values oriented - towards the black level. Do not assume any other correlation of - values with the signal level. For example, the MSB does not - necessarily indicate if the signal is 'high' or 'low' because 128 - may not be the mean value of the signal. Drivers shall not convert - the sample format by software. - - - .. row 5 - - - __u32 - - - ``start``\ [#f2]_ - - - This is the scanning system line number associated with the first - line of the VBI image, of the first and the second field - respectively. See :ref:`vbi-525` and :ref:`vbi-625` for valid - values. The ``V4L2_VBI_ITU_525_F1_START``, - ``V4L2_VBI_ITU_525_F2_START``, ``V4L2_VBI_ITU_625_F1_START`` and - ``V4L2_VBI_ITU_625_F2_START`` defines give the start line numbers - for each field for each 525 or 625 line format as a convenience. - Don't forget that ITU line numbering starts at 1, not 0. VBI input - drivers can return start values 0 if the hardware cannot reliable - identify scanning lines, VBI acquisition may not require this - information. - - - .. row 6 - - - __u32 - - - ``count``\ [#f2]_ - - - The number of lines in the first and second field image, - respectively. - - - .. row 7 - - - :cspan:`2` - - Drivers should be as flexibility as possible. For example, it may - be possible to extend or move the VBI capture window down to the - picture area, implementing a 'full field mode' to capture data - service transmissions embedded in the picture. - - An application can set the first or second ``count`` value to zero - if no data is required from the respective field; ``count``\ [1] - if the scanning system is progressive, i. e. not interlaced. The - corresponding start value shall be ignored by the application and - driver. Anyway, drivers may not support single field capturing and - return both count values non-zero. - - Both ``count`` values set to zero, or line numbers are outside the - bounds depicted\ [#f4]_, or a field image covering lines of two - fields, are invalid and shall not be returned by the driver. - - To initialize the ``start`` and ``count`` fields, applications - must first determine the current video standard selection. The - :ref:`v4l2_std_id <v4l2-std-id>` or the ``framelines`` field - of struct :c:type:`v4l2_standard` can be evaluated - for this purpose. - - - .. row 8 - - - __u32 - - - ``flags`` - - - See :ref:`vbifmt-flags` below. Currently only drivers set flags, - applications must set this field to zero. - - - .. row 9 - - - __u32 - - - ``reserved``\ [#f2]_ - - - This array is reserved for future extensions. Drivers and - applications must set it to zero. + * - __u32 + - ``sampling_rate`` + - Samples per second, i. e. unit 1 Hz. + * - __u32 + - ``offset`` + - Horizontal offset of the VBI image, relative to the leading edge + of the line synchronization pulse and counted in samples: The + first sample in the VBI image will be located ``offset`` / + ``sampling_rate`` seconds following the leading edge. See also + :ref:`vbi-hsync`. + * - __u32 + - ``samples_per_line`` + - + * - __u32 + - ``sample_format`` + - Defines the sample format as in :ref:`pixfmt`, a + four-character-code. [#f2]_ Usually this is ``V4L2_PIX_FMT_GREY``, + i. e. each sample consists of 8 bits with lower values oriented + towards the black level. Do not assume any other correlation of + values with the signal level. For example, the MSB does not + necessarily indicate if the signal is 'high' or 'low' because 128 + may not be the mean value of the signal. Drivers shall not convert + the sample format by software. + * - __u32 + - ``start``\ [#f2]_ + - This is the scanning system line number associated with the first + line of the VBI image, of the first and the second field + respectively. See :ref:`vbi-525` and :ref:`vbi-625` for valid + values. The ``V4L2_VBI_ITU_525_F1_START``, + ``V4L2_VBI_ITU_525_F2_START``, ``V4L2_VBI_ITU_625_F1_START`` and + ``V4L2_VBI_ITU_625_F2_START`` defines give the start line numbers + for each field for each 525 or 625 line format as a convenience. + Don't forget that ITU line numbering starts at 1, not 0. VBI input + drivers can return start values 0 if the hardware cannot reliable + identify scanning lines, VBI acquisition may not require this + information. + * - __u32 + - ``count``\ [#f2]_ + - The number of lines in the first and second field image, + respectively. + * - :cspan:`2` + + Drivers should be as flexibility as possible. For example, it may + be possible to extend or move the VBI capture window down to the + picture area, implementing a 'full field mode' to capture data + service transmissions embedded in the picture. + + An application can set the first or second ``count`` value to zero + if no data is required from the respective field; ``count``\ [1] + if the scanning system is progressive, i. e. not interlaced. The + corresponding start value shall be ignored by the application and + driver. Anyway, drivers may not support single field capturing and + return both count values non-zero. + + Both ``count`` values set to zero, or line numbers are outside the + bounds depicted\ [#f4]_, or a field image covering lines of two + fields, are invalid and shall not be returned by the driver. + + To initialize the ``start`` and ``count`` fields, applications + must first determine the current video standard selection. The + :ref:`v4l2_std_id <v4l2-std-id>` or the ``framelines`` field + of struct :c:type:`v4l2_standard` can be evaluated + for this purpose. + * - __u32 + - ``flags`` + - See :ref:`vbifmt-flags` below. Currently only drivers set flags, + applications must set this field to zero. + * - __u32 + - ``reserved``\ [#f2]_ + - This array is reserved for future extensions. Drivers and + applications must set it to zero. .. tabularcolumns:: |p{4.0cm}|p{1.5cm}|p{12.0cm}| @@ -235,40 +192,30 @@ and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does :stub-columns: 0 :widths: 3 1 4 - - - .. row 1 - - - ``V4L2_VBI_UNSYNC`` - - - 0x0001 - - - This flag indicates hardware which does not properly distinguish - between fields. Normally the VBI image stores the first field - (lower scanning line numbers) first in memory. This may be a top - or bottom field depending on the video standard. When this flag is - set the first or second field may be stored first, however the - fields are still in correct temporal order with the older field - first in memory. [#f3]_ - - - .. row 2 - - - ``V4L2_VBI_INTERLACED`` - - - 0x0002 - - - By default the two field images will be passed sequentially; all - lines of the first field followed by all lines of the second field - (compare :ref:`field-order` ``V4L2_FIELD_SEQ_TB`` and - ``V4L2_FIELD_SEQ_BT``, whether the top or bottom field is first in - memory depends on the video standard). When this flag is set, the - two fields are interlaced (cf. ``V4L2_FIELD_INTERLACED``). The - first line of the first field followed by the first line of the - second field, then the two second lines, and so on. Such a layout - may be necessary when the hardware has been programmed to capture - or output interlaced video images and is unable to separate the - fields for VBI capturing at the same time. For simplicity setting - this flag implies that both ``count`` values are equal and - non-zero. + * - ``V4L2_VBI_UNSYNC`` + - 0x0001 + - This flag indicates hardware which does not properly distinguish + between fields. Normally the VBI image stores the first field + (lower scanning line numbers) first in memory. This may be a top + or bottom field depending on the video standard. When this flag is + set the first or second field may be stored first, however the + fields are still in correct temporal order with the older field + first in memory. [#f3]_ + * - ``V4L2_VBI_INTERLACED`` + - 0x0002 + - By default the two field images will be passed sequentially; all + lines of the first field followed by all lines of the second field + (compare :ref:`field-order` ``V4L2_FIELD_SEQ_TB`` and + ``V4L2_FIELD_SEQ_BT``, whether the top or bottom field is first in + memory depends on the video standard). When this flag is set, the + two fields are interlaced (cf. ``V4L2_FIELD_INTERLACED``). The + first line of the first field followed by the first line of the + second field, then the two second lines, and so on. Such a layout + may be necessary when the hardware has been programmed to capture + or output interlaced video images and is unable to separate the + fields for VBI capturing at the same time. For simplicity setting + this flag implies that both ``count`` values are equal and + non-zero. |
