2024-09-09 08:52:07 +00:00
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<refentry>
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<refmeta>
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<refentrytitle>V4L2_PIX_FMT_NV12MT ('TM12')</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname id="V4L2-PIX-FMT-NV12MT"><constant>V4L2_PIX_FMT_NV12MT
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</constant></refname>
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<refpurpose>Formats with ½ horizontal and vertical
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chroma resolution. This format has two planes - one for luminance and one for
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chrominance. Chroma samples are interleaved. The difference to
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<constant>V4L2_PIX_FMT_NV12</constant> is the memory layout. Pixels are
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grouped in macroblocks of 64x32 size. The order of macroblocks in memory is
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also not standard.
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<para>This is the two-plane versions of the YUV 4:2:0 format where data
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is grouped into 64x32 macroblocks. The three components are separated into two
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sub-images or planes. The Y plane has one byte per pixel and pixels are grouped
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into 64x32 macroblocks. The CbCr plane has the same width, in bytes, as the Y
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plane (and the image), but is half as tall in pixels. The chroma plane is also
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grouped into 64x32 macroblocks.</para>
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<para>Width of the buffer has to be aligned to the multiple of 128, and
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2024-09-09 08:57:42 +00:00
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height alignment is 32. Every four adjacent buffers - two horizontally and two
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2024-09-09 08:52:07 +00:00
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vertically are grouped together and are located in memory in Z or flipped Z
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order. </para>
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<para>Layout of macroblocks in memory is presented in the following
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figure.</para>
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<para><figure id="nv12mt">
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<title><constant>V4L2_PIX_FMT_NV12MT</constant> macroblock Z shape
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memory layout</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="nv12mt.gif" format="GIF" />
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</imageobject>
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</mediaobject>
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</figure>
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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 resolution
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of macroblocks is odd then the last row of macroblocks is arranged in a linear
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order. </para>
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<para>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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</para>
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<example>
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<title>Memory layout of macroblocks in <constant>V4L2_PIX_FMT_NV12
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</constant> format pixel image - extreme case</title>
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<para>
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<figure id="nv12mt_ex">
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<title>Example <constant>V4L2_PIX_FMT_NV12MT</constant> memory
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layout of macroblocks</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="nv12mt_example.gif" format="GIF" />
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</imageobject>
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</mediaobject>
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</figure>
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Memory layout of macroblocks of <constant>V4L2_PIX_FMT_NV12MT
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</constant> format in most extreme case.
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</para>
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</example>
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</refsect1>
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</refentry>
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