Inside each MCU, every component contributes a fixed number of 8-by-8 blocks in a fixed order. Today you work out that count per component, the interleave pattern the scan decoder walks.
Compute how many 8-by-8 blocks each component contributes to one MCU, and the total blocks per MCU.
Within one MCU, a component contributes exactly H*V blocks - its horizontal factor times its vertical factor - arranged as an H-by-V grid. For 4:2:0 luma (2x2) that is four 8-by-8 blocks covering the MCU’s 16-by-16 luma area, while each chroma component (1x1) contributes a single block covering the whole MCU at half resolution. That makes six blocks per MCU: four Y, one Cb, one Cr.
The order matters enormously for the scan decoder. Blocks are interleaved component by component, each in row-major order: all of component 1’s blocks first (top-left, top-right, bottom-left, bottom-right for a 2x2), then component 2’s, then component 3’s, then the next MCU. That fixed sequence is the exact order the entropy decoder will read blocks in, and each component keeps its own DC predictor across the whole scan. With the block layout pinned down, the frame is fully understood and you are ready to crack open the entropy scan.
// a component contributes H*V blocks to each MCU, laid out// in row-major order within its H-by-V grid.// total = sum over components of H*V.func blocksPerMCU(comps []Component) (perComp []int, total int) { }