FunPack Hybrid Euler 2S Sampler

This node outputs a ComfyUI SAMPLER and can also take optional SIGMAS input and output modified SIGMAS for use with SamplerCustomAdvanced / CustomSamplerAdvanced.

Purpose

It is designed as a quality/speed compromise between:

euler_ancestral: fast, reliable, one model evaluation per step
deterministic 2S-style ODE refinement: higher quality, but more expensive because it needs extra evaluations

This sampler keeps classic Euler ancestral for the early "structure building" stage where motion, anatomy and main composition are forming. On the late denoise steps it switches to a deterministic Euler / DPM-Solver++(2S) ODE refinement path where fine detail and cleanup usually matter most.

It can also apply optional early/mid motion pulses for single-clip image-to-video workflows. These pulses add monotonic noise kicks at selected normal denoise steps instead of inserting upward sigma jumps. This is intended to push LTX2.3 away from stale frame-1 reference stiffness while avoiding the audio damage caused by Restart replay.

Recommended wiring

Use this node with SamplerCustomAdvanced or CustomSamplerAdvanced:

connect your base scheduler output into this node's optional sigmas input
connect this node's sampler output into the sampler input
connect this node's sigmas output into the sigmas input

Parameters

eta: Ancestral stochasticity at the start of sampling. 1.0 keeps normal ancestral behaviour.

eta_final: Eta value at the quality phase boundary. When set below eta, ancestral noise strength decays linearly toward this value as sigma approaches the quality phase. Lower values give a cleaner hand-off into deterministic refinement. Set equal to eta to disable decay.

s_noise: Noise multiplier for ancestral noise injection.

high_quality_pct: Fraction of the late denoise steps that switch from Euler ancestral into deterministic quality refinement. Example: 0.35 means the last 35% of steps use the ODE refinement path.

correction_blend: Blend between late-step Euler ODE and late-step 2S correction for the second half of quality-phase steps.

0.0 = pure late-step Euler ODE
1.0 = full late-step DPM++(2S)-style correction

motion_pulse_mode: Anti-stiffness motion pulse preset:

off: preserve legacy sampler behavior.
balanced: one moderate early/mid pulse.
aggressive: at least two stronger early/mid pulses for stale image-to-video generations.
custom: use the transition count, spacing, and strength exactly as configured.

motion_pulse_start_pct: Sampling progress point where the first motion pulse is applied.

motion_pulse_count: Number of requested early/mid motion pulses. Pulses that would land in the late quality phase are skipped.

motion_pulse_spacing_pct: Progress spacing between motion pulses.

motion_pulse_strength: Strength of the monotonic noise kick. Higher values push harder against stale image references, with more drift risk.

velocity_bias_mode: Experimental early velocity steering mode.

velocity_bias_strength: Strength for applying captured early velocity bias. Keep this low; 0.0 disables the applied delta.

velocity_refinement_key: In-memory key used to group captured velocity directions.

velocity_aspect_bucket: Optional grouping value such as landscape, portrait, square, ultrawide, or vertical.

sigmas: Optional incoming sigma schedule. If connected, the node returns the same schedule plus sampler-side metadata for motion pulses.

Recommended starting values

eta = 1.0, eta_final = 1.0
s_noise = 1.0
high_quality_pct = 0.30 to 0.40
correction_blend = 1.0
motion_pulse_mode = off for baseline testing
velocity_bias_mode = off

To smooth the transition into the quality phase, try eta_final = 0.5. This decays ancestral noise from 1.0 at the start toward 0.5 as sigma approaches the quality boundary.

For an aggressive LTX2.3 image-to-video motion test:

high_quality_pct = 0.35
correction_blend = 1.0
motion_pulse_mode = aggressive
motion_pulse_start_pct = 0.30
motion_pulse_count = 2
motion_pulse_spacing_pct = 0.22
motion_pulse_strength = 0.85

Expected behavior

Compared to plain euler_ancestral, this sampler should usually:

preserve more late-stage detail
clean up texture and edge quality better
keep the early motion/anatomy formation more lively
cost less than running a heavier deterministic solver for the whole schedule

The early phase uses a second-order denoised extrapolation (Adams-Bashforth 2-step) that reuses the previous step's denoised estimate to improve the score direction at no extra model-call cost. The quality phase uses progressive correction blending: the first half of quality steps use single-eval Euler ODE, the second half use the full configured 2S correction, concentrating the expensive second model call where sigma is lowest.

Motion pulse state resets after any pulse fires because the pulse modifies the latent and invalidates the previous denoised estimate.

The outgoing SIGMAS remain monotonic. Motion pulses happen inside the sampler at selected denoise steps rather than by expanding the schedule.

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