Name

VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream

Synopsis

.. c:macro:: VIDIOC_G_ENC_INDEX

int ioctl(int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp)

Arguments

fd File descriptor returned by :c:func:open().

argp Pointer to struct :c:type:v4l2_enc_idx.

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 :c:type: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.

.. tabularcolumns:: |p{4.2cm}|p{6.2cm}|p{6.9cm}|

.. c:type:: v4l2_enc_idx

.. flat-table:: struct v4l2_enc_idx :header-rows: 0 :stub-columns: 0 :widths: 1 3 8

* - __u32
  - ``entries``
  - The number of entries the driver stored in the ``entry`` array.
* - __u32
  - ``entries_cap``
  - The number of entries the driver can buffer. Must be greater than
zero.
* - __u32
  - ``reserved``\ [4]
  - Reserved for future extensions. Drivers must set the
array to zero.
* - struct :c:type:`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``.

.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|

.. c:type:: v4l2_enc_idx_entry

.. flat-table:: struct v4l2_enc_idx_entry :header-rows: 0 :stub-columns: 0 :widths: 1 1 2

* - __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.
* - __u64
  - ``pts``
  - The 33 bit *Presentation Time Stamp* of this picture as defined in
:ref:`mpeg2part1`.
* - __u32
  - ``length``
  - The length of this picture in bytes.
* - __u32
  - ``flags``
  - Flags containing the coding type of this picture, see
:ref:`enc-idx-flags`.
* - __u32
  - ``reserved``\ [2]
  - Reserved for future extensions. Drivers must set the array to
zero.

.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|

.. _enc-idx-flags:

.. flat-table:: Index Entry Flags :header-rows: 0 :stub-columns: 0 :widths: 3 1 4

* - ``V4L2_ENC_IDX_FRAME_I``
  - 0x00
  - This is an Intra-coded picture.
* - ``V4L2_ENC_IDX_FRAME_P``
  - 0x01
  - This is a Predictive-coded picture.
* - ``V4L2_ENC_IDX_FRAME_B``
  - 0x02
  - This is a Bidirectionally predictive-coded picture.
* - ``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.