mast-aigv-detection-snn

name: mast-aigv-detection-snn description: "MAST (Multi-channel pseudo-event SNN with Adaptive Spiking Temporal integrators) — first SNN-based detector for AI-generated videos. Converts inter-frame residuals into pseudo-events processed by spike-driven temporal branch with learnable per-channel time constants, fused with frozen X-CLIP semantic trajectory encoder. Achieves 93.14% cross-generator accuracy on GenVideo. Activation: AI-generated video detection, SNN video detection, temporal artifact detection, pseudo-event conversion, cross-generator generalization, MAST, spike-driven temporal integration, AIGV detection, boundary-localized firing, SDT-V3."

MAST: Multi-channel pseudo-event SNN with Adaptive Spiking Temporal integrators for AIGV Detection

First SNN-based detector for AI-generated video detection, leveraging the natural alignment between SNN event-driven sparse dynamics and the sparse, boundary-localized temporal artifacts in AI-generated videos.

Metadata

• Source: arXiv:2605.05895
• Authors: Minsuk Jang, Yujin Yang, Heeseon Kim, Minseok Son, Younghun Kim, Changick Kim
• Published: 2026-05-07
• Category: cs.CV, cs.AI
• Institution: KAIST

Core Problem

Modern AI-generated videos are photorealistic at the single-frame level. Detection must rely on temporal structure — whether motion, change, and semantic evolution remain natural over time. Prior detectors degrade sharply under cross-generator evaluation, where artifact type and timescale vary across generators.

Key Insight

AI-generated videos exhibit two complementary temporal signatures:

1. Pixel level: Smoother frame-to-frame temporal residuals with late-accumulating residual dynamics

   • Spectral centroid f_c is 3× to 13× lower for generators than real videos
   • Gap widens in later frames due to error accumulation under conditional generation

2. Semantic level: More compact trajectories in feature space

   • X-CLIP trajectory convex-hull volume is 2× to 6× smaller for generators
   • Angular curvature θ significantly reduced

3. Boundary-localized SNN firing: When raw video is fed to SNNs, fake clips elicit firing predominantly at object and motion boundaries (unlike real clips), suggesting SNN responds to temporal artifacts localized at edges

   • Boundary Fire (BF) rate is 1.3×+ higher for fakes across all generators
   • Interior Fire (IF) stays close to real — additional firing concentrates on boundary ring

This makes SNNs a natural choice for AIGV detection: their event-driven, sparsely-activated dynamics align with the structure of the residual signal in a way that dense ANN backbones do not.

MAST Architecture

Overview

MAST combines two complementary pathways:

1. Spike-Driven Temporal Branch (SDTB) — processes multi-channel temporal residuals as pseudo-events with learnable per-channel time constants
2. Frozen Semantic Encoder — X-CLIP trajectory encoder for semantic-level temporal coherence

1. Pseudo-Event Front-End

Converts inter-frame residuals into spike-like events:

ΔHF_t = |Lap(Y_t) - Lap(Y_{t-1})|          # High-frequency Laplacian residual
ΔSobel_t = |Sobel(Y_t) - Sobel(Y_{t-1})|    # Sobel edge residual
ΔAbsDiff_t = |Y_t - Y_{t-1}|                 # Absolute difference
ΔDiff2_t = |Y_t - 2Y_{t-1} + Y_{t-2}|       # Second-order difference

Each channel is converted to pseudo-events via soft thresholding:

E_{t,c} = σ((|ΔF_{t,c}| - c_th) / β)

where c_th = 0.10 (contrast threshold) and β = 0.025 (temperature), matching physical event camera semantics.

Note: Chroma channel was tested but excluded — provided no additional signal for detection.

2. Spike-Driven Temporal Branch (SDTB)

Architecture:

• PerChannelLIF — per-channel LIF with learnable τ_c and V_{th,c}
• SDT-V3 Gate — Spiking Transformer with spike separable convolutions
• MultiSpike (L=4) — output values in {0, 1, 2, 3, 4} for richer spike communication
• Spike Anomaly Gate — adaptive spike integration with learnable timescales
• Linear attention (O(N D²)) instead of full attention (O(N² D)) for efficiency

PerChannelLIF dynamics:

v_t^{(c)} = (1 - 1/τ_c) * v_{t-1}^{(c)} + x_t^{(c)}
s_t^{(c)} = Spike(v_t^{(c)}, V_{th,c})
v_t^{(c)} ← v_t^{(c)} - s_t^{(c)} * V_{th,c}  # soft reset

Parameters:

• τ_c ∈ [0.5, 20.0] — learnable time constant per channel
• V_{th,c} ∈ [0.05, 10.0] — learnable firing threshold per channel
• Both stored in log space and recovered via exp() to keep strictly positive
• Initialized at base values (τ_0 = 2.0, V_{th,0} = 1.0)

3. Semantic Trajectory Encoder

• X-CLIP-B/16 (frozen) — text-aligned video encoder
• Extracts per-frame embeddings from video encoder
• Computes trajectory curvature as auxiliary cue
• Cross-frame attention provides temporal coherence at semantic level

Why X-CLIP? Its cross-frame attention mechanism computes each embedding in temporal context of the entire clip, encoding short-range temporal coherence at semantic level — complementary to pixel-level residual dynamics of SDTB.

4. Fusion & Classification

final_logit = σ(W_t * z_t + W_s * z_s + b)

where z_t is SDTB output and z_s is semantic trajectory output.

Training Details

Auxiliary Objectives

Critical Training Pitfall

Under "Main BCE only" (without auxiliary losses), the SDTB goes silent in the first epoch:

• Gate bias keeps sigmoid output below 0.15
• L=4 Multispike requires v/V_th > 0.5 to fire
• Xavier-initialized convolutions don't produce this
• Leaky integrator accumulates membrane potentials → NaN logits → training collapse
• Under DDP with find_unused_parameters=true → extra ALLREDUCE on NaN tensor → NCCL watchdog deadlock

Solution: The spike-rate regularizer (L_rate) forces non-zero firing rate from the first epoch, keeping SDTB gradient alive.

Results

GenVideo Cross-Generator (Pika-trained)

This matches or surpasses the strongest ANN-based detectors.

Energy Efficiency

SNN gate adds only +0.10% on top of backbone; matched ANN gate adds +6.62%. 69× energy savings for the gate at parameter parity.

GenVidBench Main Task

Underperforms on flow-based generators (MuseV, SVD) — pseudo-event residuals align better with diffusion-style temporal artifacts.

SEINE Configuration

MAST achieves 77.41% mACC under SEINE training — significantly below Pika-trained (93.14%) due to:

1. SEINE is frame-interpolation generator → spike gate adapts to low spike density
2. Training/test clips sit at opposite ends of temporal-smoothness axis
3. Temporal subsampling shortcut doesn't transfer to 24 fps test generators

Implementation Guide

Prerequisites

• PyTorch
• Pre-trained X-CLIP-B/16 (frozen)
• GenVidBench or GenVideo dataset
• 4× NVIDIA RTX 3090 GPUs (recommended)

Pseudo-Event Conversion

def compute_pseudo_events(frames):
    """Convert video frames to pseudo-event tensor.
    
    frames: [B, T, C, H, W] normalized to [0, 1]
    returns: [B, T, C_events, H', W'] pseudo-event tensor
    """
    T = frames.shape[1]
    events = []
    
    for t in range(1, T):
        # High-frequency Laplacian residual
        lap_t = laplacian(frames[:, t])
        lap_tm1 = laplacian(frames[:, t-1])
        hf = torch.abs(lap_t - lap_tm1)
        
        # Sobel edge residual
        sobel_t = sobel(frames[:, t])
        sobel_tm1 = sobel(frames[:, t-1])
        sobel_res = torch.abs(sobel_t - sobel_tm1)
        
        # Absolute difference
        abs_diff = torch.abs(frames[:, t] - frames[:, t-1])
        
        # Second-order difference
        if t >= 2:
            diff2 = torch.abs(frames[:, t] - 2*frames[:, t-1] + frames[:, t-2])
        else:
            diff2 = abs_diff  # fallback
        
        # Stack channels
        event_t = torch.stack([hf, sobel_res, abs_diff, diff2], dim=1)
        
        # Soft threshold to pseudo-events
        c_th = 0.10
        beta = 0.025
        event_t = torch.sigmoid((event_t - c_th) / beta)
        
        events.append(event_t)
    
    return torch.stack(events, dim=1)

PerChannelLIF

class PerChannelLIF(nn.Module):
    def __init__(self, n_channels, tau_base=2.0, vth_base=1.0):
        super().__init__()
        # Stored in log space for positivity
        self.log_tau = nn.Parameter(torch.zeros(n_channels))
        self.log_vth = nn.Parameter(torch.zeros(n_channels))
        
        # Initialize at base values
        nn.init.constant_(self.log_tau, math.log(tau_base))
        nn.init.constant_(self.log_vth, math.log(vth_base))
    
    def forward(self, x):
        """x: [B, C, T] input tensor"""
        tau = torch.exp(self.log_tau).clamp(0.5, 20.0)
        vth = torch.exp(self.log_vth).clamp(0.05, 10.0)
        
        B, C, T = x.shape
        v = torch.zeros(B, C, device=x.device)
        spikes = []
        
        for t in range(T):
            # LIF dynamics per channel
            v = (1 - 1/tau.unsqueeze(0)) * v + x[:, :, t]
            # MultiSpike (L=4)
            s = torch.clamp(v / vth.unsqueeze(0), 0, 4.5).round()
            spikes.append(s)
            v = v - s * vth.unsqueeze(0)  # soft reset
        
        return torch.stack(spikes, dim=2)

ATan Surrogate Gradient

class MultiSpikeATan(torch.autograd.Function):
    @staticmethod
    def forward(ctx, v, vth, L=4, alpha=2.0):
        ctx.save_for_backward(v, torch.tensor(vth), torch.tensor(L), torch.tensor(alpha))
        return torch.clamp(v / vth, 0, L + 0.5).round()
    
    @staticmethod
    def backward(ctx, grad_output):
        v, vth, L, alpha = ctx.saved_tensors
        L = int(L)
        
        # Sum ATan kernels at each integer threshold
        grad = torch.zeros_like(grad_output)
        for k in range(L):
            threshold = k + 0.5
            grad += alpha / (2 * (1 + ((v - threshold) * alpha / 2) ** 2))
        
        # Clip: zero gradient outside saturating range
        mask = (v > 0) & (v < L)
        grad = grad_output * grad * mask.float()
        
        return grad, None, None, None

Applications

• AI-generated video detection: Cross-generator generalization across 10+ unseen generators
• Deepfake detection: Temporal artifact detection in synthetic media
• Content authentication: Verifying video provenance and authenticity
• Neuromorphic deployment: Energy-efficient detection on edge devices
• Temporal anomaly detection: Generalizable to any domain with temporal artifacts

Advantages Over ANN-Based Detectors

Pitfalls

1. Training silence/deadlock: Without spike-rate regularization, SDTB goes silent in epoch 1, leading to NaN and NCCL deadlock. Always include L_rate penalty.
2. SEINE training configuration: Underperforms (77.41% vs 93.14%) due to temporal-smoothness distribution mismatch. Train on generators with diverse temporal artifacts.
3. Flow-based generators: Underperforms on MuseV/SVD where ReStraV is stronger. Pseudo-event residuals align better with diffusion-style artifacts.
4. Chroma channel: Tested but excluded — provides no additional detection signal. Don't waste compute on color residuals.
5. X-CLIP choice: Other text-aligned encoders (ViCLIP, InternVideo2) and generic video backbones (VideoMamba) underperform. X-CLIP's cross-frame attention is key.
6. Firing rate target: r* = 0.15 is critical — too high wastes energy, too low causes silence.
7. Soft vs hard reset: Soft reset is default; hard reset available as option but not used in experiments.

Related Skills

• spiking-neural-network-analysis
• snn-learning-survey
• spiking-oscillation-mapping
• edgespike-edge-iot-snn
• snn-performance-analysis
• spike-sparsity-deployment-cost
• quantization-spiking-neural-networks-beyond-accuracy
• sd-tv3-spike-driven-transformer