What causes "Unknown strategy: {strategy}" in Comfy-Org/ComfyUI?

Set strategy to 'uniform' (evenly spaced frames) or 'random' (seeded random selection).

Comfy-Org/ComfyUI · error · ValueError

Unknown strategy: {strategy}

Error message

Unknown strategy: {strategy}

What it means

Thrown by the video frame-sampling node when the 'strategy' input is neither 'uniform' nor 'random'. The node dispatches on an if/elif chain over the strategy string and treats anything else as a programming/validation error. In practice only a mismatched frontend enum, a hand-edited workflow JSON, or a custom node sending a raw string reaches it.

Source

Thrown at comfy_extras/nodes_dataset.py:1266

            return io.NodeOutput(
                video.as_trimmed(0.0, num_frames / fps, strict_duration=False)
            )
        if strategy == "tail":
            start_t = (total_frames - num_frames) / fps
            return io.NodeOutput(
                video.as_trimmed(start_t, num_frames / fps, strict_duration=False)
            )

        if strategy == "uniform":
            if num_frames == 1:
                indices = [total_frames // 2]
            else:
                indices = [round(i * (total_frames - 1) / (num_frames - 1)) for i in range(num_frames)]
        elif strategy == "random":
            rng = np.random.RandomState(seed % (2**32 - 1))
            indices = sorted(rng.choice(total_frames, size=num_frames, replace=False).tolist())
        else:
            raise ValueError(f"Unknown strategy: {strategy}")

        return io.NodeOutput(_decode_selected_frames(video, indices))


class VideoTemporalCropNode(io.ComfyNode):
    """Crop a continuous range of frames from a video (fully lazy)."""

    @classmethod
    def define_schema(cls):
        return io.Schema(
            node_id="VideoTemporalCrop",
            search_aliases=["crop", "crop video", "temporal crop", "truncate video"],
            display_name="Crop Video (Temporal)",
            category="video/transform",
            description="Crop a continuous range of frames from a video.",
            is_experimental=True,
            inputs=[
                io.Video.Input("video", tooltip="Input video."),

View on GitHub (pinned to 1c6d8d45b3)

Solutions

Set strategy to 'uniform' (evenly spaced frames) or 'random' (seeded random selection).
Open the node in the ComfyUI UI and re-pick the strategy from the dropdown, then re-save the workflow.
If you are generating the prompt programmatically, validate strategy against ['uniform','random'] before queueing.

Example fix

// before (workflow JSON)
"inputs": { "strategy": "evenly", ... }
// after
"inputs": { "strategy": "uniform", ... }

Defensive patterns

Strategy: validation

Validate before calling

VALID_STRATEGIES = {'uniform', 'random'}
assert strategy in VALID_STRATEGIES, f'strategy must be one of {sorted(VALID_STRATEGIES)}, got {strategy!r}'

Type guard

def is_valid_strategy(s: str) -> bool:
    return s in {'uniform', 'random'}

Prevention

Always pick enum inputs from the node dropdown rather than typing them into workflow JSON.
When generating prompts programmatically, validate enum fields against the node's advertised options before queueing.
Avoid hand-porting strategy names from other sampler nodes.

When it happens

Trigger: Calling the node with strategy set to a value outside {'uniform','random'}: e.g. a workflow file saved with 'evenly', 'stride', or a typo like 'unifrom', or a script constructing the prompt dict with an arbitrary strategy string.

Common situations: Hand-edited or LLM-generated workflow JSON with a wrong enum value; workflows migrated from another sampler node whose strategy names differ ('first', 'last', 'evenly'); custom frontends that do not enforce the combo options.

Related errors

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/9224ec0427f1f095. Report an issue: GitHub.