665 lines
22 KiB
ReStructuredText
665 lines
22 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
.. _buffer:
|
|
|
|
*******
|
|
Buffers
|
|
*******
|
|
|
|
A buffer contains data exchanged by application and driver using one of
|
|
the Streaming I/O methods. In the multi-planar API, the data is held in
|
|
planes, while the buffer structure acts as a container for the planes.
|
|
Only pointers to buffers (planes) are exchanged, the data itself is not
|
|
copied. These pointers, together with meta-information like timestamps
|
|
or field parity, are stored in a struct :c:type:`v4l2_buffer`,
|
|
argument to the :ref:`VIDIOC_QUERYBUF`,
|
|
:ref:`VIDIOC_QBUF` and
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API,
|
|
some plane-specific members of struct :c:type:`v4l2_buffer`,
|
|
such as pointers and sizes for each plane, are stored in struct
|
|
struct :c:type:`v4l2_plane` instead. In that case, struct
|
|
struct :c:type:`v4l2_buffer` contains an array of plane structures.
|
|
|
|
Dequeued video buffers come with timestamps. The driver decides at which
|
|
part of the frame and with which clock the timestamp is taken. Please
|
|
see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and
|
|
``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags
|
|
are always valid and constant across all buffers during the whole video
|
|
stream. Changes in these flags may take place as a side effect of
|
|
:ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` or
|
|
:ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` however. The
|
|
``V4L2_BUF_FLAG_TIMESTAMP_COPY`` timestamp type which is used by e.g. on
|
|
mem-to-mem devices is an exception to the rule: the timestamp source
|
|
flags are copied from the OUTPUT video buffer to the CAPTURE video
|
|
buffer.
|
|
|
|
|
|
.. c:type:: v4l2_buffer
|
|
|
|
struct v4l2_buffer
|
|
==================
|
|
|
|
.. tabularcolumns:: |p{2.8cm}|p{2.5cm}|p{1.3cm}|p{10.5cm}|
|
|
|
|
.. cssclass:: longtable
|
|
|
|
.. flat-table:: struct v4l2_buffer
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 1 2 1 10
|
|
|
|
* - __u32
|
|
- ``index``
|
|
-
|
|
- Number of the buffer, set by the application except when calling
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, then it is set by the
|
|
driver. This field can range from zero to the number of buffers
|
|
allocated with the :ref:`VIDIOC_REQBUFS` ioctl
|
|
(struct :c:type:`v4l2_requestbuffers`
|
|
``count``), plus any buffers allocated with
|
|
:ref:`VIDIOC_CREATE_BUFS` minus one.
|
|
* - __u32
|
|
- ``type``
|
|
-
|
|
- Type of the buffer, same as struct
|
|
:c:type:`v4l2_format` ``type`` or struct
|
|
:c:type:`v4l2_requestbuffers` ``type``, set
|
|
by the application. See :c:type:`v4l2_buf_type`
|
|
* - __u32
|
|
- ``bytesused``
|
|
-
|
|
- The number of bytes occupied by the data in the buffer. It depends
|
|
on the negotiated data format and may change with each buffer for
|
|
compressed variable size data like JPEG images. Drivers must set
|
|
this field when ``type`` refers to a capture stream, applications
|
|
when it refers to an output stream. If the application sets this
|
|
to 0 for an output stream, then ``bytesused`` will be set to the
|
|
size of the buffer (see the ``length`` field of this struct) by
|
|
the driver. For multiplanar formats this field is ignored and the
|
|
``planes`` pointer is used instead.
|
|
* - __u32
|
|
- ``flags``
|
|
-
|
|
- Flags set by the application or driver, see :ref:`buffer-flags`.
|
|
* - __u32
|
|
- ``field``
|
|
-
|
|
- Indicates the field order of the image in the buffer, see
|
|
:c:type:`v4l2_field`. This field is not used when the buffer
|
|
contains VBI data. Drivers must set it when ``type`` refers to a
|
|
capture stream, applications when it refers to an output stream.
|
|
* - struct timeval
|
|
- ``timestamp``
|
|
-
|
|
- For capture streams this is time when the first data byte was
|
|
captured, as returned by the :c:func:`clock_gettime()` function
|
|
for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in
|
|
:ref:`buffer-flags`. For output streams the driver stores the
|
|
time at which the last data byte was actually sent out in the
|
|
``timestamp`` field. This permits applications to monitor the
|
|
drift between the video and system clock. For output streams that
|
|
use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill
|
|
in the timestamp which will be copied by the driver to the capture
|
|
stream.
|
|
* - struct :c:type:`v4l2_timecode`
|
|
- ``timecode``
|
|
-
|
|
- When ``type`` is ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` and the
|
|
``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this
|
|
structure contains a frame timecode. In
|
|
:c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
|
|
bottom field contain the same timecode. Timecodes are intended to
|
|
help video editing and are typically recorded on video tapes, but
|
|
also embedded in compressed formats like MPEG. This field is
|
|
independent of the ``timestamp`` and ``sequence`` fields.
|
|
* - __u32
|
|
- ``sequence``
|
|
-
|
|
- Set by the driver, counting the frames (not fields!) in sequence.
|
|
This field is set for both input and output devices.
|
|
* - :cspan:`3`
|
|
|
|
In :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
|
|
bottom field have the same sequence number. The count starts at
|
|
zero and includes dropped or repeated frames. A dropped frame was
|
|
received by an input device but could not be stored due to lack of
|
|
free buffer space. A repeated frame was displayed again by an
|
|
output device because the application did not pass new data in
|
|
time.
|
|
|
|
.. note::
|
|
|
|
This may count the frames received e.g. over USB, without
|
|
taking into account the frames dropped by the remote hardware due
|
|
to limited compression throughput or bus bandwidth. These devices
|
|
identify by not enumerating any video standards, see
|
|
:ref:`standard`.
|
|
|
|
* - __u32
|
|
- ``memory``
|
|
-
|
|
- This field must be set by applications and/or drivers in
|
|
accordance with the selected I/O method. See :c:type:`v4l2_memory`
|
|
* - union
|
|
- ``m``
|
|
* -
|
|
- __u32
|
|
- ``offset``
|
|
- For the single-planar API and when ``memory`` is
|
|
``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the
|
|
start of the device memory. The value is returned by the driver
|
|
and apart of serving as parameter to the
|
|
:ref:`mmap() <func-mmap>` function not useful for applications.
|
|
See :ref:`mmap` for details
|
|
* -
|
|
- unsigned long
|
|
- ``userptr``
|
|
- For the single-planar API and when ``memory`` is
|
|
``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to
|
|
unsigned long type) in virtual memory, set by the application. See
|
|
:ref:`userp` for details.
|
|
* -
|
|
- struct v4l2_plane
|
|
- ``*planes``
|
|
- When using the multi-planar API, contains a userspace pointer to
|
|
an array of struct :c:type:`v4l2_plane`. The size of
|
|
the array should be put in the ``length`` field of this
|
|
struct :c:type:`v4l2_buffer` structure.
|
|
* -
|
|
- int
|
|
- ``fd``
|
|
- For the single-plane API and when ``memory`` is
|
|
``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with
|
|
a DMABUF buffer.
|
|
* - __u32
|
|
- ``length``
|
|
-
|
|
- Size of the buffer (not the payload) in bytes for the
|
|
single-planar API. This is set by the driver based on the calls to
|
|
:ref:`VIDIOC_REQBUFS` and/or
|
|
:ref:`VIDIOC_CREATE_BUFS`. For the
|
|
multi-planar API the application sets this to the number of
|
|
elements in the ``planes`` array. The driver will fill in the
|
|
actual number of valid elements in that array.
|
|
* - __u32
|
|
- ``reserved2``
|
|
-
|
|
- A place holder for future extensions. Drivers and applications
|
|
must set this to 0.
|
|
* - __u32
|
|
- ``reserved``
|
|
-
|
|
- A place holder for future extensions. Drivers and applications
|
|
must set this to 0.
|
|
|
|
|
|
|
|
.. c:type:: v4l2_plane
|
|
|
|
struct v4l2_plane
|
|
=================
|
|
|
|
.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
|
|
|
|
.. cssclass:: longtable
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 1 1 1 2
|
|
|
|
* - __u32
|
|
- ``bytesused``
|
|
-
|
|
- The number of bytes occupied by data in the plane (its payload).
|
|
Drivers must set this field when ``type`` refers to a capture
|
|
stream, applications when it refers to an output stream. If the
|
|
application sets this to 0 for an output stream, then
|
|
``bytesused`` will be set to the size of the plane (see the
|
|
``length`` field of this struct) by the driver.
|
|
|
|
.. note::
|
|
|
|
Note that the actual image data starts at ``data_offset``
|
|
which may not be 0.
|
|
* - __u32
|
|
- ``length``
|
|
-
|
|
- Size in bytes of the plane (not its payload). This is set by the
|
|
driver based on the calls to
|
|
:ref:`VIDIOC_REQBUFS` and/or
|
|
:ref:`VIDIOC_CREATE_BUFS`.
|
|
* - union
|
|
- ``m``
|
|
-
|
|
-
|
|
* -
|
|
- __u32
|
|
- ``mem_offset``
|
|
- When the memory type in the containing struct
|
|
:c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this
|
|
is the value that should be passed to :ref:`mmap() <func-mmap>`,
|
|
similar to the ``offset`` field in struct
|
|
:c:type:`v4l2_buffer`.
|
|
* -
|
|
- unsigned long
|
|
- ``userptr``
|
|
- When the memory type in the containing struct
|
|
:c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``,
|
|
this is a userspace pointer to the memory allocated for this plane
|
|
by an application.
|
|
* -
|
|
- int
|
|
- ``fd``
|
|
- When the memory type in the containing struct
|
|
:c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``,
|
|
this is a file descriptor associated with a DMABUF buffer, similar
|
|
to the ``fd`` field in struct :c:type:`v4l2_buffer`.
|
|
* - __u32
|
|
- ``data_offset``
|
|
-
|
|
- Offset in bytes to video data in the plane. Drivers must set this
|
|
field when ``type`` refers to a capture stream, applications when
|
|
it refers to an output stream.
|
|
|
|
.. note::
|
|
|
|
That data_offset is included in ``bytesused``. So the
|
|
size of the image in the plane is ``bytesused``-``data_offset``
|
|
at offset ``data_offset`` from the start of the plane.
|
|
* - __u32
|
|
- ``reserved[11]``
|
|
-
|
|
- Reserved for future use. Should be zeroed by drivers and
|
|
applications.
|
|
|
|
|
|
|
|
.. c:type:: v4l2_buf_type
|
|
|
|
enum v4l2_buf_type
|
|
==================
|
|
|
|
.. cssclass:: longtable
|
|
|
|
.. tabularcolumns:: |p{7.2cm}|p{0.6cm}|p{9.7cm}|
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 4 1 9
|
|
|
|
* - ``V4L2_BUF_TYPE_VIDEO_CAPTURE``
|
|
- 1
|
|
- Buffer of a single-planar video capture stream, see
|
|
:ref:`capture`.
|
|
* - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``
|
|
- 9
|
|
- Buffer of a multi-planar video capture stream, see
|
|
:ref:`capture`.
|
|
* - ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
|
|
- 2
|
|
- Buffer of a single-planar video output stream, see
|
|
:ref:`output`.
|
|
* - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``
|
|
- 10
|
|
- Buffer of a multi-planar video output stream, see :ref:`output`.
|
|
* - ``V4L2_BUF_TYPE_VIDEO_OVERLAY``
|
|
- 3
|
|
- Buffer for video overlay, see :ref:`overlay`.
|
|
* - ``V4L2_BUF_TYPE_VBI_CAPTURE``
|
|
- 4
|
|
- Buffer of a raw VBI capture stream, see :ref:`raw-vbi`.
|
|
* - ``V4L2_BUF_TYPE_VBI_OUTPUT``
|
|
- 5
|
|
- Buffer of a raw VBI output stream, see :ref:`raw-vbi`.
|
|
* - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE``
|
|
- 6
|
|
- Buffer of a sliced VBI capture stream, see :ref:`sliced`.
|
|
* - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``
|
|
- 7
|
|
- Buffer of a sliced VBI output stream, see :ref:`sliced`.
|
|
* - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``
|
|
- 8
|
|
- Buffer for video output overlay (OSD), see :ref:`osd`.
|
|
* - ``V4L2_BUF_TYPE_SDR_CAPTURE``
|
|
- 11
|
|
- Buffer for Software Defined Radio (SDR) capture stream, see
|
|
:ref:`sdr`.
|
|
* - ``V4L2_BUF_TYPE_SDR_OUTPUT``
|
|
- 12
|
|
- Buffer for Software Defined Radio (SDR) output stream, see
|
|
:ref:`sdr`.
|
|
|
|
|
|
|
|
.. _buffer-flags:
|
|
|
|
Buffer Flags
|
|
============
|
|
|
|
.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
|
|
|
|
.. cssclass:: longtable
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 3 1 4
|
|
|
|
* .. _`V4L2-BUF-FLAG-MAPPED`:
|
|
|
|
- ``V4L2_BUF_FLAG_MAPPED``
|
|
- 0x00000001
|
|
- The buffer resides in device memory and has been mapped into the
|
|
application's address space, see :ref:`mmap` for details.
|
|
Drivers set or clear this flag when the
|
|
:ref:`VIDIOC_QUERYBUF`,
|
|
:ref:`VIDIOC_QBUF` or
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the
|
|
driver.
|
|
* .. _`V4L2-BUF-FLAG-QUEUED`:
|
|
|
|
- ``V4L2_BUF_FLAG_QUEUED``
|
|
- 0x00000002
|
|
- Internally drivers maintain two buffer queues, an incoming and
|
|
outgoing queue. When this flag is set, the buffer is currently on
|
|
the incoming queue. It automatically moves to the outgoing queue
|
|
after the buffer has been filled (capture devices) or displayed
|
|
(output devices). Drivers set or clear this flag when the
|
|
``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling
|
|
the ``VIDIOC_QBUF``\ ioctl it is always set and after
|
|
``VIDIOC_DQBUF`` always cleared.
|
|
* .. _`V4L2-BUF-FLAG-DONE`:
|
|
|
|
- ``V4L2_BUF_FLAG_DONE``
|
|
- 0x00000004
|
|
- When this flag is set, the buffer is currently on the outgoing
|
|
queue, ready to be dequeued from the driver. Drivers set or clear
|
|
this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After
|
|
calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always
|
|
cleared. Of course a buffer cannot be on both queues at the same
|
|
time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag
|
|
are mutually exclusive. They can be both cleared however, then the
|
|
buffer is in "dequeued" state, in the application domain so to
|
|
say.
|
|
* .. _`V4L2-BUF-FLAG-ERROR`:
|
|
|
|
- ``V4L2_BUF_FLAG_ERROR``
|
|
- 0x00000040
|
|
- When this flag is set, the buffer has been dequeued successfully,
|
|
although the data might have been corrupted. This is recoverable,
|
|
streaming may continue as normal and the buffer may be reused
|
|
normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is
|
|
called.
|
|
* .. _`V4L2-BUF-FLAG-KEYFRAME`:
|
|
|
|
- ``V4L2_BUF_FLAG_KEYFRAME``
|
|
- 0x00000008
|
|
- Drivers set or clear this flag when calling the ``VIDIOC_DQBUF``
|
|
ioctl. It may be set by video capture devices when the buffer
|
|
contains a compressed image which is a key frame (or field), i. e.
|
|
can be decompressed on its own. Also known as an I-frame.
|
|
Applications can set this bit when ``type`` refers to an output
|
|
stream.
|
|
* .. _`V4L2-BUF-FLAG-PFRAME`:
|
|
|
|
- ``V4L2_BUF_FLAG_PFRAME``
|
|
- 0x00000010
|
|
- Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames
|
|
or fields which contain only differences to a previous key frame.
|
|
Applications can set this bit when ``type`` refers to an output
|
|
stream.
|
|
* .. _`V4L2-BUF-FLAG-BFRAME`:
|
|
|
|
- ``V4L2_BUF_FLAG_BFRAME``
|
|
- 0x00000020
|
|
- Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional
|
|
predicted frame or field which contains only the differences
|
|
between the current frame and both the preceding and following key
|
|
frames to specify its content. Applications can set this bit when
|
|
``type`` refers to an output stream.
|
|
* .. _`V4L2-BUF-FLAG-TIMECODE`:
|
|
|
|
- ``V4L2_BUF_FLAG_TIMECODE``
|
|
- 0x00000100
|
|
- The ``timecode`` field is valid. Drivers set or clear this flag
|
|
when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set
|
|
this bit and the corresponding ``timecode`` structure when
|
|
``type`` refers to an output stream.
|
|
* .. _`V4L2-BUF-FLAG-PREPARED`:
|
|
|
|
- ``V4L2_BUF_FLAG_PREPARED``
|
|
- 0x00000400
|
|
- The buffer has been prepared for I/O and can be queued by the
|
|
application. Drivers set or clear this flag when the
|
|
:ref:`VIDIOC_QUERYBUF`,
|
|
:ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`,
|
|
:ref:`VIDIOC_QBUF` or
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called.
|
|
* .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`:
|
|
|
|
- ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE``
|
|
- 0x00000800
|
|
- Caches do not have to be invalidated for this buffer. Typically
|
|
applications shall use this flag if the data captured in the
|
|
buffer is not going to be touched by the CPU, instead the buffer
|
|
will, probably, be passed on to a DMA-capable hardware unit for
|
|
further processing or output.
|
|
* .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`:
|
|
|
|
- ``V4L2_BUF_FLAG_NO_CACHE_CLEAN``
|
|
- 0x00001000
|
|
- Caches do not have to be cleaned for this buffer. Typically
|
|
applications shall use this flag for output buffers if the data in
|
|
this buffer has not been created by the CPU but by some
|
|
DMA-capable unit, in which case caches have not been used.
|
|
* .. _`V4L2-BUF-FLAG-LAST`:
|
|
|
|
- ``V4L2_BUF_FLAG_LAST``
|
|
- 0x00100000
|
|
- Last buffer produced by the hardware. mem2mem codec drivers set
|
|
this flag on the capture queue for the last buffer when the
|
|
:ref:`VIDIOC_QUERYBUF` or
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to
|
|
hardware limitations, the last buffer may be empty. In this case
|
|
the driver will set the ``bytesused`` field to 0, regardless of
|
|
the format. Any Any subsequent call to the
|
|
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
|
|
but return an ``EPIPE`` error code.
|
|
* .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`:
|
|
|
|
- ``V4L2_BUF_FLAG_TIMESTAMP_MASK``
|
|
- 0x0000e000
|
|
- Mask for timestamp types below. To test the timestamp type, mask
|
|
out bits not belonging to timestamp type by performing a logical
|
|
and operation with buffer flags and timestamp mask.
|
|
* .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`:
|
|
|
|
- ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN``
|
|
- 0x00000000
|
|
- Unknown timestamp type. This type is used by drivers before Linux
|
|
3.9 and may be either monotonic (see below) or realtime (wall
|
|
clock). Monotonic clock has been favoured in embedded systems
|
|
whereas most of the drivers use the realtime clock. Either kinds
|
|
of timestamps are available in user space via
|
|
:c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC``
|
|
and ``CLOCK_REALTIME``, respectively.
|
|
* .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`:
|
|
|
|
- ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC``
|
|
- 0x00002000
|
|
- The buffer timestamp has been taken from the ``CLOCK_MONOTONIC``
|
|
clock. To access the same clock outside V4L2, use
|
|
:c:func:`clock_gettime`.
|
|
* .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`:
|
|
|
|
- ``V4L2_BUF_FLAG_TIMESTAMP_COPY``
|
|
- 0x00004000
|
|
- The CAPTURE buffer timestamp has been taken from the corresponding
|
|
OUTPUT buffer. This flag applies only to mem2mem devices.
|
|
* .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`:
|
|
|
|
- ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK``
|
|
- 0x00070000
|
|
- Mask for timestamp sources below. The timestamp source defines the
|
|
point of time the timestamp is taken in relation to the frame.
|
|
Logical 'and' operation between the ``flags`` field and
|
|
``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the
|
|
timestamp source. Applications must set the timestamp source when
|
|
``type`` refers to an output stream and
|
|
``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set.
|
|
* .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`:
|
|
|
|
- ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF``
|
|
- 0x00000000
|
|
- End Of Frame. The buffer timestamp has been taken when the last
|
|
pixel of the frame has been received or the last pixel of the
|
|
frame has been transmitted. In practice, software generated
|
|
timestamps will typically be read from the clock a small amount of
|
|
time after the last pixel has been received or transmitten,
|
|
depending on the system and other activity in it.
|
|
* .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`:
|
|
|
|
- ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE``
|
|
- 0x00010000
|
|
- Start Of Exposure. The buffer timestamp has been taken when the
|
|
exposure of the frame has begun. This is only valid for the
|
|
``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
|
|
|
|
|
|
|
|
.. c:type:: v4l2_memory
|
|
|
|
enum v4l2_memory
|
|
================
|
|
|
|
.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 3 1 4
|
|
|
|
* - ``V4L2_MEMORY_MMAP``
|
|
- 1
|
|
- The buffer is used for :ref:`memory mapping <mmap>` I/O.
|
|
* - ``V4L2_MEMORY_USERPTR``
|
|
- 2
|
|
- The buffer is used for :ref:`user pointer <userp>` I/O.
|
|
* - ``V4L2_MEMORY_OVERLAY``
|
|
- 3
|
|
- [to do]
|
|
* - ``V4L2_MEMORY_DMABUF``
|
|
- 4
|
|
- The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O.
|
|
|
|
|
|
|
|
Timecodes
|
|
=========
|
|
|
|
The struct :c:type:`v4l2_timecode` structure is designed to hold a
|
|
:ref:`smpte12m` or similar timecode. (struct
|
|
struct :c:type:`timeval` timestamps are stored in struct
|
|
:c:type:`v4l2_buffer` field ``timestamp``.)
|
|
|
|
|
|
.. c:type:: v4l2_timecode
|
|
|
|
struct v4l2_timecode
|
|
--------------------
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - __u32
|
|
- ``type``
|
|
- Frame rate the timecodes are based on, see :ref:`timecode-type`.
|
|
* - __u32
|
|
- ``flags``
|
|
- Timecode flags, see :ref:`timecode-flags`.
|
|
* - __u8
|
|
- ``frames``
|
|
- Frame count, 0 ... 23/24/29/49/59, depending on the type of
|
|
timecode.
|
|
* - __u8
|
|
- ``seconds``
|
|
- Seconds count, 0 ... 59. This is a binary, not BCD number.
|
|
* - __u8
|
|
- ``minutes``
|
|
- Minutes count, 0 ... 59. This is a binary, not BCD number.
|
|
* - __u8
|
|
- ``hours``
|
|
- Hours count, 0 ... 29. This is a binary, not BCD number.
|
|
* - __u8
|
|
- ``userbits``\ [4]
|
|
- The "user group" bits from the timecode.
|
|
|
|
|
|
|
|
.. _timecode-type:
|
|
|
|
Timecode Types
|
|
--------------
|
|
|
|
.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 3 1 4
|
|
|
|
* - ``V4L2_TC_TYPE_24FPS``
|
|
- 1
|
|
- 24 frames per second, i. e. film.
|
|
* - ``V4L2_TC_TYPE_25FPS``
|
|
- 2
|
|
- 25 frames per second, i. e. PAL or SECAM video.
|
|
* - ``V4L2_TC_TYPE_30FPS``
|
|
- 3
|
|
- 30 frames per second, i. e. NTSC video.
|
|
* - ``V4L2_TC_TYPE_50FPS``
|
|
- 4
|
|
-
|
|
* - ``V4L2_TC_TYPE_60FPS``
|
|
- 5
|
|
-
|
|
|
|
|
|
|
|
.. _timecode-flags:
|
|
|
|
Timecode Flags
|
|
--------------
|
|
|
|
.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}|
|
|
|
|
.. flat-table::
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 3 1 4
|
|
|
|
* - ``V4L2_TC_FLAG_DROPFRAME``
|
|
- 0x0001
|
|
- Indicates "drop frame" semantics for counting frames in 29.97 fps
|
|
material. When set, frame numbers 0 and 1 at the start of each
|
|
minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the
|
|
count.
|
|
* - ``V4L2_TC_FLAG_COLORFRAME``
|
|
- 0x0002
|
|
- The "color frame" flag.
|
|
* - ``V4L2_TC_USERBITS_field``
|
|
- 0x000C
|
|
- Field mask for the "binary group flags".
|
|
* - ``V4L2_TC_USERBITS_USERDEFINED``
|
|
- 0x0000
|
|
- Unspecified format.
|
|
* - ``V4L2_TC_USERBITS_8BITCHARS``
|
|
- 0x0008
|
|
- 8-bit ISO characters.
|