145 lines
4.1 KiB
ReStructuredText
145 lines
4.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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.. _VIDIOC_G_ENC_INDEX:
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************************
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ioctl VIDIOC_G_ENC_INDEX
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************************
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Name
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====
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VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream
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Synopsis
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========
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.. c:macro:: VIDIOC_G_ENC_INDEX
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``int ioctl(int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp)``
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open()`.
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``argp``
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Pointer to struct :c:type:`v4l2_enc_idx`.
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Description
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===========
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The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed
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video stream the same or another application currently reads from the
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driver, which is useful for random access into the stream without
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decoding it.
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To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a
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pointer to a struct :c:type:`v4l2_enc_idx`. On success
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the driver fills the ``entry`` array, stores the number of elements
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written in the ``entries`` field, and initializes the ``entries_cap``
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field.
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Each element of the ``entry`` array contains meta data about one
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picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to
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``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up
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to ``entries_cap`` entries. This number can be lower or higher than
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``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to
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read the meta data in time the oldest entries will be lost. When the
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buffer is empty or no capturing/encoding is in progress, ``entries``
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will be zero.
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Currently this ioctl is only defined for MPEG-2 program streams and
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video elementary streams.
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.. tabularcolumns:: |p{4.2cm}|p{6.2cm}|p{6.9cm}|
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.. c:type:: v4l2_enc_idx
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.. flat-table:: struct v4l2_enc_idx
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 3 8
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* - __u32
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- ``entries``
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- The number of entries the driver stored in the ``entry`` array.
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* - __u32
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- ``entries_cap``
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- The number of entries the driver can buffer. Must be greater than
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zero.
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* - __u32
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- ``reserved``\ [4]
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- Reserved for future extensions. Drivers must set the
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array to zero.
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* - struct :c:type:`v4l2_enc_idx_entry`
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- ``entry``\ [``V4L2_ENC_IDX_ENTRIES``]
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- Meta data about a compressed video stream. Each element of the
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array corresponds to one picture, sorted in ascending order by
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their ``offset``.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
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.. c:type:: v4l2_enc_idx_entry
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.. flat-table:: struct v4l2_enc_idx_entry
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u64
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- ``offset``
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- The offset in bytes from the beginning of the compressed video
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stream to the beginning of this picture, that is a *PES packet
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header* as defined in :ref:`mpeg2part1` or a *picture header* as
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defined in :ref:`mpeg2part2`. When the encoder is stopped, the
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driver resets the offset to zero.
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* - __u64
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- ``pts``
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- The 33 bit *Presentation Time Stamp* of this picture as defined in
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:ref:`mpeg2part1`.
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* - __u32
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- ``length``
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- The length of this picture in bytes.
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* - __u32
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- ``flags``
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- Flags containing the coding type of this picture, see
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:ref:`enc-idx-flags`.
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* - __u32
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- ``reserved``\ [2]
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- Reserved for future extensions. Drivers must set the array to
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zero.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
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.. _enc-idx-flags:
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.. flat-table:: Index Entry Flags
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_ENC_IDX_FRAME_I``
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- 0x00
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- This is an Intra-coded picture.
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* - ``V4L2_ENC_IDX_FRAME_P``
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- 0x01
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- This is a Predictive-coded picture.
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* - ``V4L2_ENC_IDX_FRAME_B``
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- 0x02
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- This is a Bidirectionally predictive-coded picture.
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* - ``V4L2_ENC_IDX_FRAME_MASK``
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- 0x0F
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- *AND* the flags field with this mask to obtain the picture coding
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type.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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