 NV12M

NV12M is the non-contiguous-memory variant of NV12 in the Linux video API. It stores eight-bit luma separately from an interleaved Cb, Cr plane, using 4:2:0 chroma subsampling. Its two image memory planes can occupy independent allocations; the second plane's address is not inferred by adding the first plane's size.^[ref]

For an original address example, stipulate an accepted width-six, height-four layout. Let the luma base be 1000 with framebuffer stride eight bytes, and the colour-difference base be 8000 with stride 12 bytes. The allocations occupy $4(8)=32$ and $2(12)=24$ bytes, respectively. Their 56 allocated bytes contain 36 active samples, with padding accounting for the difference.

At zero-based luma position $(r,c)=(3,5)$, the address is $1000+3(8)+5=1029$. In the declared subsampling grid, its associated colour-difference cell is $(1,2)$. The Cb address is $8000+1(12)+2(2)=8016$, and Cr is at 8017. Substituting 1032 for the second base would access an unrelated region under these stipulated allocations.

The V4L2 multi-planar API describes each memory plane explicitly. It also supports single-planar formats, so using that API does not itself prove that a buffer is NV12M. The negotiated pixel format, plane addresses, sizes and strides must agree.^[ref]

This separation changes buffer organization, not the YCbCr matrix, code ranges or chroma sample location. Those remain additional information needed for colour interpretation and chroma reconstruction.