2.6.25. V4L2_PIX_FMT_NV12MT (‘TM12’)

Formats with ½ horizontal and vertical chroma resolution. This format has two planes - one for luminance and one for chrominance. Chroma samples are interleaved. The difference to V4L2_PIX_FMT_NV12 is the memory layout. Pixels are grouped in macroblocks of 64x32 size. The order of macroblocks in memory is also not standard.

2.6.25.1. Description

This is the two-plane versions of the YUV 4:2:0 format where data is grouped into 64x32 macroblocks. The three components are separated into two sub-images or planes. The Y plane has one byte per pixel and pixels are grouped into 64x32 macroblocks. The CbCr plane has the same width, in bytes, as the Y plane (and the image), but is half as tall in pixels. The chroma plane is also grouped into 64x32 macroblocks.

Width of the buffer has to be aligned to the multiple of 128, and height alignment is 32. Every four adjacent buffers - two horizontally and two vertically are grouped together and are located in memory in Z or flipped Z order.

Layout of macroblocks in memory is presented in the following figure.

V4L2_PIX_FMT_NV12MT macroblock Z shape memory layout

The requirement that width is multiple of 128 is implemented because, the Z shape cannot be cut in half horizontally. In case the vertical resolution of macroblocks is odd then the last row of macroblocks is arranged in a linear order.

In case of chroma the layout is identical. Cb and Cr samples are interleaved. Height of the buffer is aligned to 32.

Example V4L2_PIX_FMT_NV12MT memory layout of macroblocks

Memory layout of macroblocks of V4L2_PIX_FMT_NV12MT format in most extreme case.