diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst new file mode 100644 index 000000000000..7e3142e11d77 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst @@ -0,0 +1,159 @@ +.. 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/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _VIDIOC_ENUM_FMT: + +********************* +ioctl VIDIOC_ENUM_FMT +********************* + +Name +==== + +VIDIOC_ENUM_FMT - Enumerate image formats + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp ) + :name: VIDIOC_ENUM_FMT + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to struct :c:type:`v4l2_fmtdesc`. + + +Description +=========== + +To enumerate image formats applications initialize the ``type`` and +``index`` field of struct :c:type:`v4l2_fmtdesc` and call +the :ref:`VIDIOC_ENUM_FMT` ioctl with a pointer to this structure. Drivers +fill the rest of the structure or return an ``EINVAL`` error code. All +formats are enumerable by beginning at index zero and incrementing by +one until ``EINVAL`` is returned. If applicable, drivers shall return +formats in preference order, where preferred formats are returned before +(that is, with lower ``index`` value) less-preferred formats. + +.. note:: + + After switching input or output the list of enumerated image + formats may be different. + + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| + +.. c:type:: v4l2_fmtdesc + +.. flat-table:: struct v4l2_fmtdesc + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u32 + - ``index`` + - Number of the format in the enumeration, set by the application. + This is in no way related to the ``pixelformat`` field. + * - __u32 + - ``type`` + - Type of the data stream, set by the application. Only these types + are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, + ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``, + ``V4L2_BUF_TYPE_VIDEO_OUTPUT``, + ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``, + ``V4L2_BUF_TYPE_VIDEO_OVERLAY``, + ``V4L2_BUF_TYPE_SDR_CAPTURE``, + ``V4L2_BUF_TYPE_SDR_OUTPUT`` and + ``V4L2_BUF_TYPE_META_CAPTURE``. + See :c:type:`v4l2_buf_type`. + * - __u32 + - ``flags`` + - See :ref:`fmtdesc-flags` + * - __u8 + - ``description``\ [32] + - Description of the format, a NUL-terminated ASCII string. This + information is intended for the user, for example: "YUV 4:2:2". + * - __u32 + - ``pixelformat`` + - The image format identifier. This is a four character code as + computed by the v4l2_fourcc() macro: + * - :cspan:`2` + + .. _v4l2-fourcc: + + ``#define v4l2_fourcc(a,b,c,d)`` + + ``(((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))`` + + Several image formats are already defined by this specification in + :ref:`pixfmt`. + + .. attention:: + + These codes are not the same as those used + in the Windows world. + * - __u32 + - ``reserved``\ [4] + - Reserved for future extensions. Drivers must set the array to + zero. + + + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. _fmtdesc-flags: + +.. flat-table:: Image Format Description Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_FMT_FLAG_COMPRESSED`` + - 0x0001 + - This is a compressed format. + * - ``V4L2_FMT_FLAG_EMULATED`` + - 0x0002 + - This format is not native to the device but emulated through + software (usually libv4l2), where possible try to use a native + format instead for better performance. + * - ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM`` + - 0x0004 + - The hardware decoder for this compressed bytestream format (aka coded + format) is capable of parsing a continuous bytestream. Applications do + not need to parse the bytestream themselves to find the boundaries + between frames/fields. This flag can only be used in combination with + the ``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to compressed + formats only. This flag is valid for stateful decoders only. + * - ``V4L2_FMT_FLAG_DYN_RESOLUTION`` + - 0x0008 + - Dynamic resolution switching is supported by the device for this + compressed bytestream format (aka coded format). It will notify the user + via the event ``V4L2_EVENT_SOURCE_CHANGE`` when changes in the video + parameters are detected. This flag can only be used in combination + with the ``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to + compressed formats only. It is also only applies to stateful codecs. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EINVAL + The struct :c:type:`v4l2_fmtdesc` ``type`` is not + supported or the ``index`` is out of bounds. |