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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
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Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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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{13.3cm}|
+
+.. 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{8.7cm}|
+
+.. _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.