SNF-Bench: Separating Static Drift from Natural Flow in Long-Horizon Fixed-Camera Video Generation
Organizations: Sogang University Seoul, Korea
Abstract
Long-horizon video generation is evaluated with whole-frame metrics that reward motion and temporal consistency. For fixed-camera nature scenes this creates an ambiguity: motion of water, fire, smoke, or rain is desirable, whereas motion of the background is an error. A system can therefore score well on motion while its scene drifts, or on consistency while its flow stagnates. We introduce SNF-Bench, an evaluation framework for long-horizon fixed-camera generation that partitions each scene into static support and dynamic flow and reports static fidelity, flow persistence with absolute magnitude, and drift leakage separately, never as one score. Drift leakage is interpretive context rather than a headline measurement. Each factor is validated mechanistically rather than by correlation with preference: we inject global translation, rotation, and scale drift and progressive late freezing at known severity into real generations, and require each factor to respond in its stated direction and to remain selective against corruptions it does not target. Auditing publicly released long-horizon text-conditioned checkpoints under one recorded common inference configuration, plus an image-conditioned track with released-pipeline references and a deployment-sensitivity panel, we find that whole-frame motion and static-region drift induce near-opposite orderings of the same outputs. At maximum controlled translation, fBD and NBF rise to and baseline, but whole-frame Dynamic Degree reaches only ---rewarding the corruption. SNF-Bench measures where motion occurs and whether it persists; it does not measure physical realism. Project page: https://minar09.github.io/snfbench/.
Figures & tables
| Factor | target | off-target | admitted | ||
|---|---|---|---|---|---|
| fBD | drift | +1.00 | +0.70 | 14% | ✓ |
| NBF | drift | +1.00 | +0.60 | 6% | ✓ |
| MCFF-L | freeze | +1.00 | n/a | 14% | ✓ |
| FP | freeze | +0.80 | n/a | 21% | ✓ |
| DLR | translational leakage | +1.00 | -0.80 | 5% | ✓ |
| DAR | drift | +0.90 | +1.00 | 18% | ✓ |
| Check | result |
|---|---|
| Static-mask area | 0.614–0.663 |
| Area–fBD Spearman | , exact , |
| No precipitation: NBF order | identical |
| No precipitation: fBD extremes | unchanged |
| Boundary perturbation: max. response |
| Method | fBD | NBF | MCFF E L | FP |
|---|---|---|---|---|
| 60s horizon ( ) | ||||
| CausVid | 8.08 3.15 | 9.27 4.14 | 2.87 1.96 | 0.67 0.18 |
| Self-Forcing | 11.4 3.63 | 12.7 3.97 | 10.4 2.54 | 0.44 0.22 |
| Infinite-Forcing | 7.75 3.84 | 3.65 0.88 | 1.17 0.29 | 0.63 0.22 |
| Rolling-Forcing | 16.8 3.69 | 11.2 2.70 | 3.18 1.57 | 0.75 0.29 |
| Reward-Forcing | 14.8 3.71 | 8.51 2.79 | 3.81 0.80 | 0.49 0.18 |
| Method | fBD | NBF | MCFF E L | FP |
|---|---|---|---|---|
| 60s horizon ( ) | ||||
| Causal-Forcing++ (2-step) † | 9.18 | 5.97 | 0.85 0.60 | 0.86 |
| Causal-Forcing++ (1-step) † | 5.34 | 7.05 | 0.86 0.57 | 0.77 |
| Causal-Forcing (frame-wise) † | 21.1 | 36.4 | 2.80 2.69 | 0.89 |
| Causal-Forcing++ (2-step, frame-wise) | 9.94 | 6.91 | 1.30 0.78 | 1.02 |
| Self-Forcing † | 17.3 | 5.52 | 1.50 0.69 | 0.89 |
Appendix figures & tables23 assets
Supplementary material from the paper’s appendix.
Appendix
| Factor | target | off-target | admitted | ||
|---|---|---|---|---|---|
| fBD | drift | +1.00 | +0.70 | 14% | ✓ |
| NBF | drift | +1.00 | +0.60 | 6% | ✓ |
| MCFF-L | freeze | +1.00 | n/a | 14% | ✓ |
| FP | freeze | +0.80 | n/a | 21% | ✓ |
| DLR | translational leakage | +1.00 | -0.80 | 5% | ✓ |
| DAR | drift | +0.90 | +1.00 | 18% | ✓ |
| System | static-region area |
|---|---|
| CausVid | 0.663 0.073 |
| Reward-Forcing | 0.661 0.060 |
| Self-Forcing | 0.651 0.087 |
| Infinite-Forcing | 0.650 0.090 |
| LongLive | 0.644 0.095 |
| Rolling-Forcing | 0.616 0.107 |
| Comparison | mean diff. | 95% CI | |
|---|---|---|---|
| Infinite-Forcing Causal-Forcing | 23 | -83.98 | |
| Infinite-Forcing LongLive | 23 | -10.22 | |
| Infinite-Forcing Self-Forcing | 23 | -9.07 | |
| Infinite-Forcing Rolling-Forcing | 23 | -7.58 | |
| Infinite-Forcing CausVid | 23 | -5.62 | |
| Infinite-Forcing Reward-Forcing | 23 | -4.86 |
| System | setting | resolution | fps | horizons |
|---|---|---|---|---|
| CausVid | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| Self-Forcing | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| Infinite-Forcing | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| Rolling-Forcing | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| Reward-Forcing | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| LongLive | common | 832 480 | 16 | 5s, 60s, 120s, 240s |
| System | setting | resolution | fps | horizons |
|---|---|---|---|---|
| Causal-Forcing++ (2-step, frame-wise) | released | 832 480 | 16 | 5s, 60s, 120s, 240s |
| Wan2.1-I2V-14B-480P | released | 832 464 | 16 | 5s |
| Wan2.2-I2V-A14B | released | 832 464 | 16 | 5s |
| LTX-Video 13B-0.9.8-distilled | released | 832 480 | 24 | 5s |
| Causal-Forcing++ (1-step, frame-wise) | released | 832 480 | 16 | 60s, 120s |
| Causal-Forcing++ (2-step) † | wrapper | 832 480 | 16 | 5s, 60s, 120s, 240s |
| track | horizon | measured | fBD abstained | rate |
|---|---|---|---|---|
| I2V | 120s | 140 | 0 | 0.0% |
| I2V | 240s | 30 | 0 | 0.0% |
| I2V | 5s | 90 | 0 | 0.0% |
| I2V | 60s | 210 | 2 | 1.0% |
| T2V | 120s | 42 | 0 | 0.0% |
| T2V | 240s | 28 | 0 | 0.0% |
| Method | status | setting | 5s | 60s | 120s | 240s |
|---|---|---|---|---|---|---|
| CausVid | public | common | V6 T6 B | V23 T23 B | V6 T6 B | V4 T4 B |
| Self-Forcing | public | common | V6 T6 B | V23 T23 B | V6 T6 B | V4 T4 B |
| Infinite-Forcing | public | common | V6 T6 B | V23 T23 B | V6 T6 B | V4 T4 B |
| Rolling-Forcing | public | common | V6 T6 B | V24 T24 B | V6 T6 B | V4 T4 B |
| Reward-Forcing | public | common | V12 T12 B | V23 T23 B | V6 T6 B | V4 T4 B |
| LongLive | public | common | V6 T6 B | V23 T23 B | V6 T6 B | V4 T4 B |
| Method | fBD | NBF | MCFF-E | MCFF-L | FP | DLR | DAR |
|---|---|---|---|---|---|---|---|
| 5s horizon ( ) | |||||||
| CausVid | 2.08 | 6.56 | 1.44 | 2.91 | 1.24 | 0.26 | 0.07 |
| Self-Forcing | 0.68 | 10.8 | 7.70 | 4.35 | 0.76 | 0.49 | 0.03 |
| Infinite-Forcing | 0.24 | 2.32 | 1.23 | 0.89 | 1.08 | 0.21 | 0.09 |
| Rolling-Forcing | 3.51 | 12.1 | 3.10 | 3.69 | 1.32 | 0.48 | 0.17 |
| Reward-Forcing | 1.10 | 5.21 | 0.63 | 0.58 | 1.37 | 0.44 | 0.28 |
| Method | setting | fBD | NBF | MCFF-E | MCFF-L | FP | DLR | DAR |
|---|---|---|---|---|---|---|---|---|
| 5s horizon ( ) | ||||||||
| Causal-Forcing++ (2-step) | wrapper | 3.69 | 10.0 | 1.06 | 0.61 | 0.78 | 0.67 | 0.32 |
| Causal-Forcing++ (1-step) | wrapper | 5.28 | 11.4 | 1.05 | 0.47 | 0.64 | 0.66 | 0.29 |
| Causal-Forcing (frame-wise) | wrapper | 16.1 | 45.3 | 8.48 | 2.79 | 0.43 | 0.68 | 0.29 |
| Causal-Forcing++ (2-step, frame-wise) | released | 1.22 | 10.6 | 2.23 | 0.78 | 0.47 | 0.68 | 0.20 |
| Self-Forcing | wrapper | 9.66 | 5.74 | 0.69 | 0.26 | 0.70 | 0.74 | 0.21 |
| System | prompt mean | rank | macro mean | rank |
| NBF | ||||
| Infinite-Forcing | 3.65 | 1 | 4.12 | 1 |
| Reward-Forcing | 8.51 | 2 | 10.11 | 4 † |
| CausVid | 9.27 | 3 | 9.93 | 3 |
| Rolling-Forcing | 11.23 | 4 | 11.32 | 5 † |
| Self-Forcing | 12.72 | 5 | 8.98 | 2 † |
| generic metric | fBD | NBF | MCFF | DLR |
|---|---|---|---|---|
| VB-DD | +0.75 | +0.93 | +0.89 | +0.36 |
| VB-bg | -0.64 | -0.71 | -0.75 | -0.50 |
| VB-smooth / VB-flick | -0.96 | -0.82 | -0.61 | -0.64 |
| Method | Generic evidence | SNF-Bench evidence | Interpretation |
|---|---|---|---|
| CausVid | VB-DD rank 6/7 | NBF rank 3/7, MCFF-L rank 4/7 | stable sequence with decaying intended motion |
| Causal-Forcing | VB-DD rank 1/7 | NBF rank 7/7, MCFF-L rank 1/7 | high apparent motion accompanied by high static-region motion under the recorded common configuration |
| Infinite-Forcing | VB-DD rank 7/7 | NBF rank 1/7, MCFF-L rank 7/7 | stable sequence with decaying intended motion |
| LongLive | VB-DD rank 3/7 | NBF rank 6/7, MCFF-L rank 3/7 | high apparent motion accompanied by high static-region motion under the recorded common configuration |
| Reward-Forcing | VB-DD rank 5/7 | NBF rank 2/7, MCFF-L rank 6/7 | stable sequence with decaying intended motion |
| Self-Forcing | VB-DD rank 2/7 | NBF rank 5/7, MCFF-L rank 2/7 | high apparent motion accompanied by high static-region motion under the recorded common configuration |
| Checkpoint | horizon | fBD | NBF | MCFF-L | DLR |
|---|---|---|---|---|---|
| Causal-Forcing++ (2-step) | 5s | +2.47 | -0.61 | -0.17 | -0.01 |
| Causal-Forcing++ (2-step) | 60s | -0.76 | -0.95 | -0.17 | -0.08 |
| Causal-Forcing++ (2-step) | 120s | -1.71 | -8.46 | -0.73 | -0.17 |
| Causal-Forcing++ (2-step) | 240s | +4.06 | +0.88 | -0.09 | -0.28 |
| Causal-Forcing++ (1-step) | 60s | -5.05 | +1.80 | +0.05 | -0.20 |
| Causal-Forcing++ (1-step) | 120s | -6.34 | +2.00 | +0.31 | -0.14 |
| Method | track | dur | n | negative | rate | most negative |
|---|---|---|---|---|---|---|
| CausVid | i2v | 120s | 20 | 1 | 5.0% | -0.055 |
| CausVid | i2v | 5s | 10 | 5 | 50.0% | -1.076 |
| CausVid | i2v | 60s | 30 | 2 | 6.7% | -0.084 |
| Causal-Forcing++ (1-step) | i2v | 120s | 20 | 1 | 5.0% | -0.027 |
| Causal-Forcing (frame-wise) | i2v | 120s | 20 | 3 | 15.0% | -0.171 |
| Causal-Forcing++ (2-step) | i2v | 5s | 10 | 1 | 10.0% | -0.164 |
| track/duration | n | river_stream | ocean_waves | precipitation | fire_smoke | lava_volcanic | windborne | cats |
|---|---|---|---|---|---|---|---|---|
| i2v/5s | 10 | 2 | · | 3 | 2 | 1 | 2 | 5 |
| i2v/60s | 30 | 9 | 4 | 9 | 1 | 3 | 4 | 6 |
| i2v/120s | 20 | 6 | 3 | 3 | 3 | 1 | 4 | 6 |
| i2v/240s | 5 | 1 | 2 | 1 | · | 1 | · | 4 |
| t2v/5s | 6 | 3 | 1 | 1 | 1 | · | · | 4 |
| t2v/60s | 23 | 14 | 2 | 3 | 2 | · | 2 | 5 |
Video Generation Evaluation
Video generation evaluation measures visual quality, prompt adherence, temporal consistency, physical plausibility, and task-specific behavior in synthesized videos.
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