xref: /linux/Documentation/userspace-api/media/v4l/metafmt-uvc.rst (revision cdd5b5a9761fd66d17586e4f4ba6588c70e640ea)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3.. _v4l2-meta-fmt-uvc:
4
5*******************************
6V4L2_META_FMT_UVC ('UVCH')
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8
9UVC Payload Header Data
10
11
12Description
13===========
14
15This format describes standard UVC metadata, extracted from UVC packet headers
16and provided by the UVC driver through metadata video nodes. That data includes
17exact copies of the standard part of UVC Payload Header contents and auxiliary
18timing information, required for precise interpretation of timestamps, contained
19in those headers. See section "2.4.3.3 Video and Still Image Payload Headers" of
20the "UVC 1.5 Class specification" for details.
21
22Each UVC payload header can be between 2 and 12 bytes large. Buffers can
23contain multiple headers, if multiple such headers have been transmitted by the
24camera for the respective frame. However, the driver may drop headers when the
25buffer is full, when they contain no useful information (e.g. those without the
26SCR field or with that field identical to the previous header), or generally to
27perform rate limiting when the device sends a large number of headers.
28
29Each individual block contains the following fields:
30
31.. flat-table:: UVC Metadata Block
32    :widths: 1 4
33    :header-rows:  1
34    :stub-columns: 0
35
36    * - Field
37      - Description
38    * - __u64 ts;
39      - system timestamp in host byte order, measured by the driver upon
40        reception of the payload
41    * - __u16 sof;
42      - USB Frame Number in host byte order, also obtained by the driver as
43        close as possible to the above timestamp to enable correlation between
44        them
45    * - :cspan:`1` *The rest is an exact copy of the UVC payload header:*
46    * - __u8 length;
47      - length of the rest of the block, including this field
48    * - __u8 flags;
49      - Flags, indicating presence of other standard UVC fields
50    * - __u8 buf[];
51      - The rest of the header, possibly including UVC PTS and SCR fields
52