nx_mp4_es.nx

nx_mp4_es.nx -- ISO-BMFF -> H.264 elementary-stream helpers, the mp4 counterpart of nx_ts_es.nx. WHY: the full mp4-to-pixels chain already existed inside nx_h264_decode_frame (proven FULL-FRAME Y+U+V BIT-EXACT vs ffmpeg on a real 45MB corpus recording), but it was reachable only through that one organ. In the corpus poster sweep the refusals were 386 unsupported_container vs 121 cabac_skipped, so the container share is the LARGER unblocked half and it needs no normative tables -- only a callable entry point. mes_find_tag -- locate a box by 4CC, returning the box start mes_spspps -- SPS/PPS from avcC, unescaped, ready for the h264 parsers mes_first_idr -- the first IDR NAL of sample 0, ready for nx_h264_decode_iframe license_tier: ORIGINAL