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54f38fcae5
Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("docs: Create a user-space API guide").
As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.
Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
68 lines
2.3 KiB
ReStructuredText
68 lines
2.3 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/userspace-api/media/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. _V4L2-PIX-FMT-NV12MT:
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****************************
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V4L2_PIX_FMT_NV12MT ('TM12')
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****************************
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Formats with ½ horizontal and vertical chroma resolution. This format
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has two planes - one for luminance and one for chrominance. Chroma
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samples are interleaved. The difference to ``V4L2_PIX_FMT_NV12`` is the
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memory layout. Pixels are grouped in macroblocks of 64x32 size. The
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order of macroblocks in memory is also not standard.
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Description
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===========
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This is the two-plane versions of the YUV 4:2:0 format where data is
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grouped into 64x32 macroblocks. The three components are separated into
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two sub-images or planes. The Y plane has one byte per pixel and pixels
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are grouped into 64x32 macroblocks. The CbCr plane has the same width,
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in bytes, as the Y plane (and the image), but is half as tall in pixels.
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The chroma plane is also grouped into 64x32 macroblocks.
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Width of the buffer has to be aligned to the multiple of 128, and height
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alignment is 32. Every four adjacent buffers - two horizontally and two
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vertically are grouped together and are located in memory in Z or
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flipped Z order.
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Layout of macroblocks in memory is presented in the following figure.
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.. _nv12mt:
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.. kernel-figure:: nv12mt.svg
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:alt: nv12mt.svg
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:align: center
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V4L2_PIX_FMT_NV12MT macroblock Z shape memory layout
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The requirement that width is multiple of 128 is implemented because,
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the Z shape cannot be cut in half horizontally. In case the vertical
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resolution of macroblocks is odd then the last row of macroblocks is
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arranged in a linear order.
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In case of chroma the layout is identical. Cb and Cr samples are
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interleaved. Height of the buffer is aligned to 32.
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.. _nv12mt_ex:
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.. kernel-figure:: nv12mt_example.svg
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:alt: nv12mt_example.svg
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:align: center
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Example V4L2_PIX_FMT_NV12MT memory layout of macroblocks
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Memory layout of macroblocks of ``V4L2_PIX_FMT_NV12MT`` format in most
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extreme case.
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