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diff --git a/Documentation/media/uapi/v4l/standard.rst b/Documentation/media/uapi/v4l/standard.rst deleted file mode 100644 index bf8959b72988..000000000000 --- a/Documentation/media/uapi/v4l/standard.rst +++ /dev/null @@ -1,192 +0,0 @@ -.. Permission is granted to copy, distribute and/or modify this -.. document under the terms of the GNU Free Documentation License, -.. Version 1.1 or any later version published by the Free Software -.. Foundation, with no Invariant Sections, no Front-Cover Texts -.. and no Back-Cover Texts. A copy of the license is included at -.. Documentation/media/uapi/fdl-appendix.rst. -.. -.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections - -.. _standard: - -*************** -Video Standards -*************** - -Video devices typically support one or more different video standards or -variations of standards. Each video input and output may support another -set of standards. This set is reported by the ``std`` field of struct -:c:type:`v4l2_input` and struct -:c:type:`v4l2_output` returned by the -:ref:`VIDIOC_ENUMINPUT` and -:ref:`VIDIOC_ENUMOUTPUT` ioctls, respectively. - -V4L2 defines one bit for each analog video standard currently in use -worldwide, and sets aside bits for driver defined standards, e. g. -hybrid standards to watch NTSC video tapes on PAL TVs and vice versa. -Applications can use the predefined bits to select a particular -standard, although presenting the user a menu of supported standards is -preferred. To enumerate and query the attributes of the supported -standards applications use the :ref:`VIDIOC_ENUMSTD` -ioctl. - -Many of the defined standards are actually just variations of a few -major standards. The hardware may in fact not distinguish between them, -or do so internal and switch automatically. Therefore enumerated -standards also contain sets of one or more standard bits. - -Assume a hypothetic tuner capable of demodulating B/PAL, G/PAL and I/PAL -signals. The first enumerated standard is a set of B and G/PAL, switched -automatically depending on the selected radio frequency in UHF or VHF -band. Enumeration gives a "PAL-B/G" or "PAL-I" choice. Similar a -Composite input may collapse standards, enumerating "PAL-B/G/H/I", -"NTSC-M" and "SECAM-D/K". [#f1]_ - -To query and select the standard used by the current video input or -output applications call the :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and -:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctl, respectively. The -*received* standard can be sensed with the -:ref:`VIDIOC_QUERYSTD` ioctl. - -.. note:: - - The parameter of all these ioctls is a pointer to a - :ref:`v4l2_std_id <v4l2-std-id>` type (a standard set), *not* an - index into the standard enumeration. Drivers must implement all video - standard ioctls when the device has one or more video inputs or outputs. - -Special rules apply to devices such as USB cameras where the notion of -video standards makes little sense. More generally for any capture or -output device which is: - -- incapable of capturing fields or frames at the nominal rate of the - video standard, or - -- that does not support the video standard formats at all. - -Here the driver shall set the ``std`` field of struct -:c:type:`v4l2_input` and struct -:c:type:`v4l2_output` to zero and the :ref:`VIDIOC_G_STD <VIDIOC_G_STD>`, -:ref:`VIDIOC_S_STD <VIDIOC_G_STD>`, :ref:`VIDIOC_QUERYSTD` and :ref:`VIDIOC_ENUMSTD` ioctls -shall return the ``ENOTTY`` error code or the ``EINVAL`` error code. - -Applications can make use of the :ref:`input-capabilities` and -:ref:`output-capabilities` flags to determine whether the video -standard ioctls can be used with the given input or output. - -Example: Information about the current video standard -===================================================== - -.. code-block:: c - - v4l2_std_id std_id; - struct v4l2_standard standard; - - if (-1 == ioctl(fd, VIDIOC_G_STD, &std_id)) { - /* Note when VIDIOC_ENUMSTD always returns ENOTTY this - is no video device or it falls under the USB exception, - and VIDIOC_G_STD returning ENOTTY is no error. */ - - perror("VIDIOC_G_STD"); - exit(EXIT_FAILURE); - } - - memset(&standard, 0, sizeof(standard)); - standard.index = 0; - - while (0 == ioctl(fd, VIDIOC_ENUMSTD, &standard)) { - if (standard.id & std_id) { - printf("Current video standard: %s\\n", standard.name); - exit(EXIT_SUCCESS); - } - - standard.index++; - } - - /* EINVAL indicates the end of the enumeration, which cannot be - empty unless this device falls under the USB exception. */ - - if (errno == EINVAL || standard.index == 0) { - perror("VIDIOC_ENUMSTD"); - exit(EXIT_FAILURE); - } - -Example: Listing the video standards supported by the current input -=================================================================== - -.. code-block:: c - - struct v4l2_input input; - struct v4l2_standard standard; - - memset(&input, 0, sizeof(input)); - - if (-1 == ioctl(fd, VIDIOC_G_INPUT, &input.index)) { - perror("VIDIOC_G_INPUT"); - exit(EXIT_FAILURE); - } - - if (-1 == ioctl(fd, VIDIOC_ENUMINPUT, &input)) { - perror("VIDIOC_ENUM_INPUT"); - exit(EXIT_FAILURE); - } - - printf("Current input %s supports:\\n", input.name); - - memset(&standard, 0, sizeof(standard)); - standard.index = 0; - - while (0 == ioctl(fd, VIDIOC_ENUMSTD, &standard)) { - if (standard.id & input.std) - printf("%s\\n", standard.name); - - standard.index++; - } - - /* EINVAL indicates the end of the enumeration, which cannot be - empty unless this device falls under the USB exception. */ - - if (errno != EINVAL || standard.index == 0) { - perror("VIDIOC_ENUMSTD"); - exit(EXIT_FAILURE); - } - -Example: Selecting a new video standard -======================================= - -.. code-block:: c - - struct v4l2_input input; - v4l2_std_id std_id; - - memset(&input, 0, sizeof(input)); - - if (-1 == ioctl(fd, VIDIOC_G_INPUT, &input.index)) { - perror("VIDIOC_G_INPUT"); - exit(EXIT_FAILURE); - } - - if (-1 == ioctl(fd, VIDIOC_ENUMINPUT, &input)) { - perror("VIDIOC_ENUM_INPUT"); - exit(EXIT_FAILURE); - } - - if (0 == (input.std & V4L2_STD_PAL_BG)) { - fprintf(stderr, "Oops. B/G PAL is not supported.\\n"); - exit(EXIT_FAILURE); - } - - /* Note this is also supposed to work when only B - or G/PAL is supported. */ - - std_id = V4L2_STD_PAL_BG; - - if (-1 == ioctl(fd, VIDIOC_S_STD, &std_id)) { - perror("VIDIOC_S_STD"); - exit(EXIT_FAILURE); - } - -.. [#f1] - Some users are already confused by technical terms PAL, NTSC and - SECAM. There is no point asking them to distinguish between B, G, D, - or K when the software or hardware can do that automatically. |