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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/dev-meta.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/userspace-api/media/v4l/dev-meta.rst | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/dev-meta.rst b/Documentation/userspace-api/media/v4l/dev-meta.rst new file mode 100644 index 000000000..8ec3a73dc --- /dev/null +++ b/Documentation/userspace-api/media/v4l/dev-meta.rst @@ -0,0 +1,67 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _metadata: + +****************** +Metadata Interface +****************** + +Metadata refers to any non-image data that supplements video frames with +additional information. This may include statistics computed over the image, +frame capture parameters supplied by the image source or device specific +parameters for specifying how the device processes images. This interface is +intended for transfer of metadata between the userspace and the hardware and +control of that operation. + +The metadata interface is implemented on video device nodes. The device can be +dedicated to metadata or can support both video and metadata as specified in its +reported capabilities. + +Querying Capabilities +===================== + +Device nodes supporting the metadata capture interface set the +``V4L2_CAP_META_CAPTURE`` flag in the ``device_caps`` field of the +:c:type:`v4l2_capability` structure returned by the :c:func:`VIDIOC_QUERYCAP` +ioctl. That flag means the device can capture metadata to memory. Similarly, +device nodes supporting metadata output interface set the +``V4L2_CAP_META_OUTPUT`` flag in the ``device_caps`` field of +:c:type:`v4l2_capability` structure. That flag means the device can read +metadata from memory. + +At least one of the read/write or streaming I/O methods must be supported. + + +Data Format Negotiation +======================= + +The metadata device uses the :ref:`format` ioctls to select the capture format. +The metadata buffer content format is bound to that selected format. In addition +to the basic :ref:`format` ioctls, the :c:func:`VIDIOC_ENUM_FMT` ioctl must be +supported as well. + +To use the :ref:`format` ioctls applications set the ``type`` field of the +:c:type:`v4l2_format` structure to ``V4L2_BUF_TYPE_META_CAPTURE`` or to +``V4L2_BUF_TYPE_META_OUTPUT`` and use the :c:type:`v4l2_meta_format` ``meta`` +member of the ``fmt`` union as needed per the desired operation. Both drivers +and applications must set the remainder of the :c:type:`v4l2_format` structure +to 0. + +.. c:type:: v4l2_meta_format + +.. tabularcolumns:: |p{1.4cm}|p{2.2cm}|p{13.9cm}| + +.. flat-table:: struct v4l2_meta_format + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u32 + - ``dataformat`` + - The data format, set by the application. This is a little endian + :ref:`four character code <v4l2-fourcc>`. V4L2 defines metadata formats + in :ref:`meta-formats`. + * - __u32 + - ``buffersize`` + - Maximum buffer size in bytes required for data. The value is set by the + driver. |