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Spec 11's first task: decide from the clip, not from assumptions, whether the
raw-tile scheme (no dictionary, tag + bitmap per changed tile) fits a 60 fps
frame. measure_wire.py extracts at 1280x960/60 fps with the hard threshold the
design requires, diffs each frame on the 40x30 picture grid, and totals the
payload a TILES_DELTA would carry:
4 + 3*count + 128*m
Full clip, 13,167 frames: mean 16,049 B/frame, p50 14,755, p95 33,353, max
51,523; 22.5% of frames exceed the 21 KB one-frame budget; 87% of changed tiles
are neither solid black nor white, so they carry a 128-byte bitmap (the design
assumed a third); mean 140 changed tiles/frame, max 1,173 at a cut. Link duty
at 60 fps would be 72% of the measured 1.27 MB/s.
Two consequences for the design, recorded here rather than discovered later:
the raw-tile scheme is borderline rather than comfortable, and the tile churn at
60 fps (140) is nearly the same as at 15 fps (165) -- motion between adjacent
60 fps frames is mostly sub-tile, so sending faster does not divide the wire by
four.