The open risk since session 2 was "a sustained action sequence could still
break the bitrate", with every clip measured so far being 1.2-1.7 s. Closed by
measurement rather than by sampling clips by hand.
07_motion_survey.py scans a whole stream at 96x72 for the hottest sliding
window of inter-frame difference. On 00223 the spread between the quietest and
hottest sustained 10 s windows is 10.6x, which is the argument for not eyeballing
it. Hottest is t=539.4s, the Singe endgame.
There, with the fixed lam the CLI uses, sasi overshoots 110 -> 129.6 KB/s (+18%)
and scsi 280 -> 373.8 KB/s (+34%). Rate control moves from "insurance, not a
fix" to required, and is promoted above the full-disc survey. The bus is not
broken -- 381.6 KB/s still fits the 488 KB/s figure -- so FINDINGS 21 survives,
at 78% of the pipe instead of a comfortable margin.
Three further corrections fall out:
- The two largest streams on the disc are bonus material. 00216 is the feature
with a burned-in commentary PiP; 00215 is the commentary. 00223 is the clean
9.4 min. A size-ranked survey would have encoded live action.
- On hard content the 256-colour scene palette (31.33 dB) binds well before the
X68000 display (40.81 dB); scsi is already within 0.51 dB of it.
- FINDINGS 24.5's architecture question resolves to "both paths, chosen per
frame": 30-53% of frames sit above the 70% crossover. Picking per frame costs
a median 37.0% of the frame budget and caps at 53.6%. Reporting for this is
wired into encode.py, which previously only printed a mean over all frames --
the one statistic that cannot answer a per-frame question.
extract.py takes optional start/dur; 08_mode_map.py renders source | decoded |
block-mode map to .webm.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
Prepares session 4 for handoff. No new measurements; this reconciles the docs
with what session 4 changed and makes the next session's entry point cheaper.
- tools/bench/check.sh re-runs both display regression tests from the Blu-ray in
~40 s and prints ALL GREEN. Verified green cold, after wiping tmp/ and
re-extracting. STATUS and README both open with it, because everything
downstream assumes the display path is pixel-exact and nothing previously
checked that in one command.
- Reconciled the figures session 4 invalidated. Session 3's 38.88 dB ceiling is
struck through in STATUS with a pointer to 40.81; the "three facts the player
must honour" table no longer quotes R20 = 0x0116, which was the 768-wide IPL
timing and would have been copied into the player as if it were the shipping
value. crtc_mode.lua is now named as the single source of truth for CRTC
registers, in both STATUS and README.
The 38.88 dB in the session-3 reproduce section is left alone and annotated
instead: it is correct for that test, which still packs I = 1. The two numbers
disagree for a reason and a reader should be able to see which is which.
- Next-step 2 now leads with something smaller than "write the decoder": a dumb
full-frame RAM->GVRAM blit in 68000 code, timed. That number alone confirms or
kills the 38% estimate, and needs no bitstream, codebooks, or DLX1 parsing.
The reference image and its checker already exist.
- Parked the user's Cliff Hanger / Lupin III follow-on in STATUS so it is not
lost and not mistaken for scheduled work. Cheaper than this project on every
axis except media prep, which is where it would actually stall.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
Session 2 reversed several of its own conclusions. The docs are append-only, so
a reader could land on a superseded section and act on it. This pass makes the
repo internally consistent.
Defects found and fixed in STATUS.md:
- claimed "Hybrid VQ with k=1024: no" as the answer to the linework question,
directly contradicting FINDINGS 14, which rejected k=1024. Both profiles are
k=256.
- malformed profile table (six column separators, five columns).
- next-steps list had two items numbered 3 and listed the full-disc survey
twice.
- the disk-benchmark section still read CRITICAL-PATH with "if SCSI sustains
>=800 KB/s, ship pixel-exact". That was written while the bandwidth figure
was misread as 4 MB/s. At 4 Mbps pixel-exact needs 92-97% of the pipe and is
not available, and the ring-buffer result means the design no longer hangs on
the benchmark at all. Rewritten with what it IS still worth doing: confirming
the 4 Mbps provenance, and confirming DMA is used rather than PIO.
FINDINGS now carries supersession blockquotes on 5, 8, 11, 17 and 18 pointing
at the sections that correct them. 18 is the dangerous one -- its peak-vs-
sustained test is reversed by 21 -- so it is marked DO NOT ACT ON THIS SECTION
while noting the per-frame data itself remains valid.
profile_gen.py had the same problem in code: it defaulted to the superseded
peak sizing and returned lam=25 where the docs say lam=10. The buffered test is
now the default and peak sizing is behind --size-for-peak as a bound only. A
tool that contradicts the findings is worse than no tool.
Also preserves the five measurement scripts that produced this session's
numbers as tools/analysis/05-09, following the session 1 precedent, and adds an
"explicitly abandoned -- do not re-propose" list to STATUS covering entropy
coding, k=1024 codebooks and flat 4x4 VQ.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
Answers session 1's critical-path question. Flat 4x4 VQ at k=256 was prototyped
and REJECTED by eye: Dirk's face disintegrates and ink outlines break into
4-pixel stair-steps. The 256-colour palettised frame is excellent, so the
palette was never the problem -- block VQ was.
Replaced it with a Cinepak-style hybrid: each 4x4 block is SKIP, one 4x4
codeword, four 2x2 codewords, or RAW literal pixels, chosen per block by
rate-distortion. The RAW escape makes lam=0 pixel-exact (measured 0.00 dB loss),
so the quality knob spans lossless to heavily-compressed in one bitstream.
Per the user's decision, ships TWO quality profiles from that one codec, one
decoder and one bitstream -- only the rate knob differs:
sasi 45 KB/s lam=300 34.8 dB stock 10MHz ACE/EXPERT
scsi 75 KB/s lam=100 35.9 dB Super/XVI or CZ-6BS1
Three corrections to earlier numbers:
1. Session 1's "183 KB/s at 12fps" was a bad extrapolation. Halving the
framerate does not halve the bitrate -- decimation roughly doubles the
per-frame delta. Re-measured directly: 340 KB/s for session 1's own RLE,
247 KB/s for changed-spans+deflate. The lossless floor is 319 MB.
2. A FOURTH false-good result, same family as the three in FINDINGS 4:
k=1024 codebooks appeared to buy +2.4 dB free, because the rate model
charged 1 byte for a 10-bit index. Charging the true cost reverses the
verdict -- k=256 wins at every matched bitrate, and by 5 dB at the low end
where the SASI profile lives. k=256 ships.
3. Stream inventory: the ~3-5MB clips are 1.2-1.7s, not ~60s, and some 60s
streams are menus, not content. Any survey must classify before averaging.
Also cleared both candidate sources for the game-logic layer: the SNES project
is MIT and DirkSimple is zlib, so the arcade scene graph can be imported and
the two transcriptions diffed against each other.
Encoder is working end-to-end: extract.py -> vq/vq_hybrid/ratectl -> encode.py,
emitting a big-endian DLX1 container the 68000 can parse with plain moves.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
Verified GVRAM is one word-access per pixel in ALL color modes; chose 256-color
256x192 with movem.l bursts (page 1 sacrificed as double-buffer).
Measured 8 scenes from the Blu-ray source: blit costs under 8% of the 12fps
cycle budget, so I/O is the bottleneck, not CPU. Naive delta+RLE reaches only
3.2:1 (365 KB/s, 470MB) -> decision to use 4x4 vector quantization (~30 KB/s).
"Shot on twos" assumption failed: the transfer has zero duplicate frames, so
12fps requires explicit decimation.
Documents three false measurement results and their root causes (per-frame
Floyd-Steinberg dithering, temporal denoise, exact-match dedupe on noisy source).
MAME Lua injection harness works and is reusable for cycle-cost measurement;
the IOCS _B_READ disk benchmark is blocked returning -1.
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
prosolis