Interim viz build: multi-visit return strip now GROUPS by pose. Each pose renders as a labeled box (Pose A = first observed frame, Pose B = mid observed frame) that LEADS with the Observed GT as the reference target on the left, followed by that method's Visit 1 / Visit 2 / Visit 3 of the SAME pose, each captioned 'Visit k'. Added the caption 'Each Observed GT is the target its same-pose visits should reproduce (GT-PSNR = visit vs this GT; self-PSNR = visit vs Visit 1)', so the obs<->visits correspondence is now unmistakable. Preserves the 倍速 speed control, lockstep sync, native-res grids, the moving-back single-pose strips, the 'Why explicit caching' motivation section, and all prior sections. Deferred (render gracefully, not yet landed): dynamic-region mover-only PSNR (n/a) and the DiT+VACE-full ablation arm (pending). [root]
4774156 verified | <!-- BEGIN mechanism (motivation: explicit cache vs learned memory) --> | |
| <section class="block"> | |
| <section id="mechanism"> | |
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| <h2>Why explicit caching, not learned memory</h2> | |
| <p class="lede">The static warp+inpaint recipe that wins the <b>static</b> benchmarks cannot represent | |
| <b>movers</b> on revisit: it can only re-project a stale earlier observation, so a moving object is | |
| smeared or frozen when the camera returns. The obvious "just learn a memory" fix — a learned | |
| key/value attention memory (MemAttn) spliced into the generator — <span class="nogo">destabilises | |
| training and collapses to colored noise</span>. What actually works is an <b>explicit, geometry-grounded | |
| rolling 4D cache</b>: it stores per-time point clouds and re-renders the mover from the correct | |
| time, beating the static warp on the true mover region.</p> | |
| <div class="kpis"> | |
| <div class="kpi"><div class="v">+1.9 dB</div><div class="k">mover PSNR — standard revisit</div></div> | |
| <div class="kpi"><div class="v">+2.7 dB</div><div class="k">mover PSNR — drift / loop-closure</div></div> | |
| <div class="kpi"><div class="v">46/50</div><div class="k">clips cache > static warp</div></div> | |
| <div class="kpi"><div class="v">25/25</div><div class="k">drift clips cache wins</div></div> | |
| </div> | |
| <p class="lede" style="font-size:.82rem;color:#6b7480;">All deltas are on the <b>true-mover region only</b> | |
| (background id 0 and >35%-area static planes excluded). An earlier prototype reported a spurious | |
| +34 dB because a mask bug counted the Kubric background as a mover; the corrected mover mask gives | |
| the honest single-digit-dB win above.</p> | |
| <h3>1 · Static warp ghosts movers; the rolling cache renders them clean</h3> | |
| <div class="panelkey">Each panel: <b>top-left</b> GT · <b>top-right</b> static warp · | |
| <b>bottom-left</b> rolling 4D-cache render · <b>bottom-right</b> cache overlaid. The static warp | |
| smears / displaces the moving objects (it can only re-project the stale observation); the rolling | |
| cache re-renders each mover at the correct time and matches GT.</div> | |
| <div class="two"> | |
| <figure><img src="assets/mechanism/warp_vs_cache_1.png" alt="static warp vs rolling cache, mover ghosting (scene A)"> | |
| <figcaption>Kubric revisit A — the flying cans/discs are ghost-streaked by the static warp | |
| (top-right) but crisp in the rolling-cache render (bottom-left).</figcaption></figure> | |
| <figure><img src="assets/mechanism/warp_vs_cache_2.png" alt="static warp vs rolling cache, mover ghosting (scene B)"> | |
| <figcaption>Kubric revisit B — the sliding bottle/shoe are frozen at the stale pose by the | |
| static warp; the cache places them at their correct return-time location.</figcaption></figure> | |
| </div> | |
| <h3>2 · Learned KV-memory (MemAttn) is a NO-GO — it collapses to colored noise</h3> | |
| <div class="panelkey">Each strip left→right: GT · observed / early return · MemAttn | |
| attempt · <b>rightmost = MemAttn output</b>. Splicing a learned key/value memory into the generator | |
| destabilises the diffusion and the return frame collapses to <span class="nogo">colored noise</span> — | |
| the same failure across scenes and away-distances, i.e. not a tuning artifact.</div> | |
| <div class="four"> | |
| <figure><img src="assets/mechanism/memattn_collapse_1.png" alt="MemAttn collapse (scn02701 b60)"> | |
| <figcaption>scn02701, away-bin 60°</figcaption></figure> | |
| <figure><img src="assets/mechanism/memattn_collapse_2.png" alt="MemAttn collapse (scn02701 b90)"> | |
| <figcaption>scn02701, away-bin 90°</figcaption></figure> | |
| <figure><img src="assets/mechanism/memattn_collapse_3.png" alt="MemAttn collapse (scn02701 b120)"> | |
| <figcaption>scn02701, away-bin 120°</figcaption></figure> | |
| <figure><img src="assets/mechanism/memattn_collapse_4.png" alt="MemAttn collapse (scn02708 b60)"> | |
| <figcaption>scn02708, away-bin 60°</figcaption></figure> | |
| </div> | |
| <div class="concl"><b>Takeaway.</b> Static warp is memory-free and cannot represent movers (stale / | |
| ghost); a learned KV-memory is unstable (colored-noise collapse). An <b>explicit geometry-grounded | |
| rolling 4D cache</b> is what closes the loop on dynamic revisits — <span class="win">+1.9 dB | |
| standard / +2.7 dB drift on the true mover region, winning 46/50 clips and 25/25 drift clips</span>. | |
| This is the scientific reason we pivoted the dynamic method to explicit caching rather than learned | |
| memory.</div> | |
| </section> | |
| </section> | |
| <!-- END mechanism --> | |