Pure-Rust H.264 (Constrained Baseline) decoder.
Parses SPS/PPS/IDR-slice headers and reconstructs I_16x16 (DC-predicted) macroblocks: CAVLC residual decode, inverse transform (incl. luma/chroma DC Hadamard), intra DC prediction. The reconstruction path is shared with the encoder so the two agree bit-for-bit. Inter prediction and deblocking land in later generations behind this same API.