Based on kernel version 6.13. Page generated on 2025-01-21 08:21 EST.
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L
.. _VIDIOC_G_JPEGCOMP:
******************************************
ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP
******************************************
Name
====
VIDIOC_G_JPEGCOMP - VIDIOC_S_JPEGCOMP
Synopsis
========
.. c:macro:: VIDIOC_G_JPEGCOMP
``int ioctl(int fd, VIDIOC_G_JPEGCOMP, v4l2_jpegcompression *argp)``
.. c:macro:: VIDIOC_S_JPEGCOMP
``int ioctl(int fd, VIDIOC_S_JPEGCOMP, const v4l2_jpegcompression *argp)``
Arguments
=========
``fd``
File descriptor returned by :c:func:`open()`.
``argp``
Pointer to struct :c:type:`v4l2_jpegcompression`.
Description
===========
These ioctls are **deprecated**. New drivers and applications should use
:ref:`JPEG class controls <jpeg-controls>` for image quality and JPEG
markers control.
[to do]
Ronald Bultje elaborates:
APP is some application-specific information. The application can set it
itself, and it'll be stored in the JPEG-encoded fields (eg; interlacing
information for in an AVI or so). COM is the same, but it's comments,
like 'encoded by me' or so.
jpeg_markers describes whether the huffman tables, quantization tables
and the restart interval information (all JPEG-specific stuff) should be
stored in the JPEG-encoded fields. These define how the JPEG field is
encoded. If you omit them, applications assume you've used standard
encoding. You usually do want to add them.
.. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{13.1cm}|
.. c:type:: v4l2_jpegcompression
.. flat-table:: struct v4l2_jpegcompression
:header-rows: 0
:stub-columns: 0
:widths: 1 1 2
* - int
- ``quality``
- Deprecated. If
:ref:`V4L2_CID_JPEG_COMPRESSION_QUALITY <jpeg-quality-control>`
control is exposed by a driver applications should use it instead
and ignore this field.
* - int
- ``APPn``
-
* - int
- ``APP_len``
-
* - char
- ``APP_data``\ [60]
-
* - int
- ``COM_len``
-
* - char
- ``COM_data``\ [60]
-
* - __u32
- ``jpeg_markers``
- See :ref:`jpeg-markers`. Deprecated. If
:ref:`V4L2_CID_JPEG_ACTIVE_MARKER <jpeg-active-marker-control>`
control is exposed by a driver applications should use it instead
and ignore this field.
.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
.. _jpeg-markers:
.. flat-table:: JPEG Markers Flags
:header-rows: 0
:stub-columns: 0
:widths: 3 1 4
* - ``V4L2_JPEG_MARKER_DHT``
- (1<<3)
- Define Huffman Tables
* - ``V4L2_JPEG_MARKER_DQT``
- (1<<4)
- Define Quantization Tables
* - ``V4L2_JPEG_MARKER_DRI``
- (1<<5)
- Define Restart Interval
* - ``V4L2_JPEG_MARKER_COM``
- (1<<6)
- Comment segment
* - ``V4L2_JPEG_MARKER_APP``
- (1<<7)
- App segment, driver will always use APP0
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.
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