128 lines
3.0 KiB
ReStructuredText
128 lines
3.0 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_G_JPEGCOMP:
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******************************************
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ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP
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******************************************
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Name
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====
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VIDIOC_G_JPEGCOMP - VIDIOC_S_JPEGCOMP
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_G_JPEGCOMP, v4l2_jpegcompression *argp )
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:name: VIDIOC_G_JPEGCOMP
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.. c:function:: int ioctl( int fd, VIDIOC_S_JPEGCOMP, const v4l2_jpegcompression *argp )
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:name: VIDIOC_S_JPEGCOMP
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_jpegcompression`.
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Description
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===========
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These ioctls are **deprecated**. New drivers and applications should use
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:ref:`JPEG class controls <jpeg-controls>` for image quality and JPEG
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markers control.
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[to do]
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Ronald Bultje elaborates:
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APP is some application-specific information. The application can set it
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itself, and it'll be stored in the JPEG-encoded fields (eg; interlacing
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information for in an AVI or so). COM is the same, but it's comments,
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like 'encoded by me' or so.
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jpeg_markers describes whether the huffman tables, quantization tables
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and the restart interval information (all JPEG-specific stuff) should be
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stored in the JPEG-encoded fields. These define how the JPEG field is
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encoded. If you omit them, applications assume you've used standard
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encoding. You usually do want to add them.
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.. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{13.3cm}|
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.. c:type:: v4l2_jpegcompression
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.. flat-table:: struct v4l2_jpegcompression
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - int
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- ``quality``
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- Deprecated. If
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:ref:`V4L2_CID_JPEG_COMPRESSION_QUALITY <jpeg-quality-control>`
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control is exposed by a driver applications should use it instead
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and ignore this field.
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* - int
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- ``APPn``
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-
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* - int
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- ``APP_len``
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-
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* - char
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- ``APP_data``\ [60]
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-
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* - int
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- ``COM_len``
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-
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* - char
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- ``COM_data``\ [60]
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-
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* - __u32
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- ``jpeg_markers``
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- See :ref:`jpeg-markers`. Deprecated. If
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:ref:`V4L2_CID_JPEG_ACTIVE_MARKER <jpeg-active-marker-control>`
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control is exposed by a driver applications should use it instead
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and ignore this field.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _jpeg-markers:
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.. flat-table:: JPEG Markers Flags
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_JPEG_MARKER_DHT``
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- (1<<3)
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- Define Huffman Tables
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* - ``V4L2_JPEG_MARKER_DQT``
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- (1<<4)
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- Define Quantization Tables
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* - ``V4L2_JPEG_MARKER_DRI``
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- (1<<5)
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- Define Restart Interval
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* - ``V4L2_JPEG_MARKER_COM``
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- (1<<6)
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- Comment segment
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* - ``V4L2_JPEG_MARKER_APP``
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- (1<<7)
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- App segment, driver will always use APP0
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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