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authorAndré Fabian Silva Delgado <emulatorman@parabola.nu>2016-10-20 00:10:27 -0300
committerAndré Fabian Silva Delgado <emulatorman@parabola.nu>2016-10-20 00:10:27 -0300
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tree7fee4ab0509879c373c4f2cbd5b8a5be5b4041ee /Documentation/media/uapi/v4l/vidioc-g-enc-index.rst
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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_G_ENC_INDEX:
+
+************************
+ioctl VIDIOC_G_ENC_INDEX
+************************
+
+Name
+====
+
+VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_enc_idx *argp )
+
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+ VIDIOC_G_ENC_INDEX
+
+``argp``
+
+
+Description
+===========
+
+The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed
+video stream the same or another application currently reads from the
+driver, which is useful for random access into the stream without
+decoding it.
+
+To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a
+pointer to a struct :ref:`v4l2_enc_idx <v4l2-enc-idx>`. On success
+the driver fills the ``entry`` array, stores the number of elements
+written in the ``entries`` field, and initializes the ``entries_cap``
+field.
+
+Each element of the ``entry`` array contains meta data about one
+picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to
+``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up
+to ``entries_cap`` entries. This number can be lower or higher than
+``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to
+read the meta data in time the oldest entries will be lost. When the
+buffer is empty or no capturing/encoding is in progress, ``entries``
+will be zero.
+
+Currently this ioctl is only defined for MPEG-2 program streams and
+video elementary streams.
+
+
+.. _v4l2-enc-idx:
+
+.. flat-table:: struct v4l2_enc_idx
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2 1 1
+
+
+ - .. row 1
+
+ - __u32
+
+ - ``entries``
+
+ - The number of entries the driver stored in the ``entry`` array.
+
+ - .. row 2
+
+ - __u32
+
+ - ``entries_cap``
+
+ - The number of entries the driver can buffer. Must be greater than
+ zero.
+
+ - .. row 3
+
+ - __u32
+
+ - ``reserved``\ [4]
+
+ - :cspan:`2` Reserved for future extensions. Drivers must set the
+ array to zero.
+
+ - .. row 4
+
+ - struct :ref:`v4l2_enc_idx_entry <v4l2-enc-idx-entry>`
+
+ - ``entry``\ [``V4L2_ENC_IDX_ENTRIES``]
+
+ - Meta data about a compressed video stream. Each element of the
+ array corresponds to one picture, sorted in ascending order by
+ their ``offset``.
+
+
+
+.. _v4l2-enc-idx-entry:
+
+.. flat-table:: struct v4l2_enc_idx_entry
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+
+ - .. row 1
+
+ - __u64
+
+ - ``offset``
+
+ - The offset in bytes from the beginning of the compressed video
+ stream to the beginning of this picture, that is a *PES packet
+ header* as defined in :ref:`mpeg2part1` or a *picture header* as
+ defined in :ref:`mpeg2part2`. When the encoder is stopped, the
+ driver resets the offset to zero.
+
+ - .. row 2
+
+ - __u64
+
+ - ``pts``
+
+ - The 33 bit *Presentation Time Stamp* of this picture as defined in
+ :ref:`mpeg2part1`.
+
+ - .. row 3
+
+ - __u32
+
+ - ``length``
+
+ - The length of this picture in bytes.
+
+ - .. row 4
+
+ - __u32
+
+ - ``flags``
+
+ - Flags containing the coding type of this picture, see
+ :ref:`enc-idx-flags`.
+
+ - .. row 5
+
+ - __u32
+
+ - ``reserved``\ [2]
+
+ - Reserved for future extensions. Drivers must set the array to
+ zero.
+
+
+
+.. _enc-idx-flags:
+
+.. flat-table:: Index Entry Flags
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+
+ - .. row 1
+
+ - ``V4L2_ENC_IDX_FRAME_I``
+
+ - 0x00
+
+ - This is an Intra-coded picture.
+
+ - .. row 2
+
+ - ``V4L2_ENC_IDX_FRAME_P``
+
+ - 0x01
+
+ - This is a Predictive-coded picture.
+
+ - .. row 3
+
+ - ``V4L2_ENC_IDX_FRAME_B``
+
+ - 0x02
+
+ - This is a Bidirectionally predictive-coded picture.
+
+ - .. row 4
+
+ - ``V4L2_ENC_IDX_FRAME_MASK``
+
+ - 0x0F
+
+ - *AND* the flags field with this mask to obtain the picture coding
+ type.
+
+
+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.