FINDINGS 26 stopped the session-5 rate controller before it shipped: it built a
lam-ladder of independent whole-sequence encodes and picked frames off it, so
SKIP blocks referenced reconstructions the decoder never saw -- 111 of 120
frames drifted. The fix is the structural one 26.1 said it had to be.
vq_hybrid is now frame-drivable -- frame_ctx / decide / paint -- and encode() is
a thin loop over it. Rate control drives the same three calls, bisects lam per
frame under the leaky bucket, and feeds back the frame it actually emitted. The
desync has no way to occur, and 09_ratectl_drift.py goes 111/120 -> 0/120. That
test is now part of check.sh, which is ~2 min rather than ~40 s.
Both overshoots on the worst sustained window are closed for under 1 dB, totals
including audio: sasi 137.4 -> 109.5 KB/s (-0.60 dB), scsi 381.6 -> 280.0 KB/s
(-0.91 dB). Zero frames hit the lam=800 cliff, so nothing was destroyed to get
there. Rate control also makes the display path cheaper -- scsi's median drops
53.6% -> 47.1% -- because raising lam moves blocks to SKIP and V1.
Two knobs measured rather than guessed. --rc-floor is worth 0.00 dB on that
window and defaults to the profile lam, so rate control cannot regress content
that already fits. --prefill defaults to 0 and is documented as a trap: it buys
a permission to overshoot of exactly bucket/nframes, and on a 14-frame clip it
disables the controller outright.
FINDINGS 26.5 was wrong in both halves and 27.6 records it. _paint was not the
bottleneck (14% of a frame, though vectorising it was still right at 17.1x) and
the ladder was never "minutes" -- those were k-means in build(). What makes
per-frame rate control affordable is that VQ.assign depends on neither lam nor
prev, so it is cached one frame deep: a 12-step search over 120 frames costs
0.31 s against 49.1 s.
Also caught: fixed-lam sasi was already 5% over target on 00020, the clip
everyone called easy. Nothing noticed because the profile table quotes PSNR and
not bitrate.
check.sh: ALL GREEN.
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
prosolis