vidioc-g-jpegcomp.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_G_JPEGCOMP:
  5
  6******************************************
  7ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP
  8******************************************
  9
 10Name
 11====
 12
 13VIDIOC_G_JPEGCOMP - VIDIOC_S_JPEGCOMP
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_G_JPEGCOMP
 19
 20``int ioctl(int fd, VIDIOC_G_JPEGCOMP, v4l2_jpegcompression *argp)``
 21
 22.. c:macro:: VIDIOC_S_JPEGCOMP
 23
 24``int ioctl(int fd, VIDIOC_S_JPEGCOMP, const v4l2_jpegcompression *argp)``
 25
 26Arguments
 27=========
 28
 29``fd``
 30    File descriptor returned by :c:func:`open()`.
 31
 32``argp``
 33    Pointer to struct :c:type:`v4l2_jpegcompression`.
 34
 35Description
 36===========
 37
 38These ioctls are **deprecated**. New drivers and applications should use
 39:ref:`JPEG class controls <jpeg-controls>` for image quality and JPEG
 40markers control.
 41
 42[to do]
 43
 44Ronald Bultje elaborates:
 45
 46APP is some application-specific information. The application can set it
 47itself, and it'll be stored in the JPEG-encoded fields (eg; interlacing
 48information for in an AVI or so). COM is the same, but it's comments,
 49like 'encoded by me' or so.
 50
 51jpeg_markers describes whether the huffman tables, quantization tables
 52and the restart interval information (all JPEG-specific stuff) should be
 53stored in the JPEG-encoded fields. These define how the JPEG field is
 54encoded. If you omit them, applications assume you've used standard
 55encoding. You usually do want to add them.
 56
 57.. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{13.1cm}|
 58
 59.. c:type:: v4l2_jpegcompression
 60
 61.. flat-table:: struct v4l2_jpegcompression
 62    :header-rows:  0
 63    :stub-columns: 0
 64    :widths:       1 1 2
 65
 66    * - int
 67      - ``quality``
 68      - Deprecated. If
 69	:ref:`V4L2_CID_JPEG_COMPRESSION_QUALITY <jpeg-quality-control>`
 70	control is exposed by a driver applications should use it instead
 71	and ignore this field.
 72    * - int
 73      - ``APPn``
 74      -
 75    * - int
 76      - ``APP_len``
 77      -
 78    * - char
 79      - ``APP_data``\ [60]
 80      -
 81    * - int
 82      - ``COM_len``
 83      -
 84    * - char
 85      - ``COM_data``\ [60]
 86      -
 87    * - __u32
 88      - ``jpeg_markers``
 89      - See :ref:`jpeg-markers`. Deprecated. If
 90	:ref:`V4L2_CID_JPEG_ACTIVE_MARKER <jpeg-active-marker-control>`
 91	control is exposed by a driver applications should use it instead
 92	and ignore this field.
 93
 94.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
 95
 96.. _jpeg-markers:
 97
 98.. flat-table:: JPEG Markers Flags
 99    :header-rows:  0
100    :stub-columns: 0
101    :widths:       3 1 4
102
103    * - ``V4L2_JPEG_MARKER_DHT``
104      - (1<<3)
105      - Define Huffman Tables
106    * - ``V4L2_JPEG_MARKER_DQT``
107      - (1<<4)
108      - Define Quantization Tables
109    * - ``V4L2_JPEG_MARKER_DRI``
110      - (1<<5)
111      - Define Restart Interval
112    * - ``V4L2_JPEG_MARKER_COM``
113      - (1<<6)
114      - Comment segment
115    * - ``V4L2_JPEG_MARKER_APP``
116      - (1<<7)
117      - App segment, driver will always use APP0
118
119Return Value
120============
121
122On success 0 is returned, on error -1 and the ``errno`` variable is set
123appropriately. The generic error codes are described at the
124:ref:`Generic Error Codes <gen-errors>` chapter.