Comfy-Org/ComfyUI · error · ValueError

Failed to slice video:\nSource duration: {video.get_duration

Error message

Failed to slice video:\nSource duration: {video.get_duration()}\nStart time: {start_time}\nTarget duration: {duration}

What it means

The video trim node delegates to video.as_trimmed(start_time, duration, strict_duration=...); when that returns None the requested slice could not be produced (typically the requested window extends beyond the source). The node then raises with source duration, start time, and target duration for diagnosis.

Source

Thrown at comfy_extras/nodes_video.py:302

                    tooltip="Duration in seconds, or 0 for unlimited duration",
                ),
                io.Boolean.Input(
                    "strict_duration",
                    default=False,
                    tooltip="If True, when the specified duration is not possible, an error will be raised.",
                ),
            ],
            outputs=[
                io.Video.Output(),
            ],
        )

    @classmethod
    def execute(cls, video: io.Video.Type, start_time: float, duration: float, strict_duration: bool) -> io.NodeOutput:
        trimmed = video.as_trimmed(start_time, duration, strict_duration=strict_duration)
        if trimmed is not None:
            return io.NodeOutput(trimmed)
        raise ValueError(
            f"Failed to slice video:\nSource duration: {video.get_duration()}\nStart time: {start_time}\nTarget duration: {duration}"
        )


class VideoExtension(ComfyExtension):
    @override
    async def get_node_list(self) -> list[type[io.ComfyNode]]:
        return [
            SaveWEBM,
            SaveVideo,
            CreateVideo,
            GetVideoComponents,
            LoadVideo,
            VideoSlice,
        ]

async def comfy_entrypoint() -> VideoExtension:
    return VideoExtension()

View on GitHub (pinned to 1c6d8d45b3)

Solutions

Read the reported source duration and clamp start_time/duration so start_time + duration <= source duration
Set strict_duration=False to allow a shorter tail slice instead of failing
Compute trim parameters dynamically from video.get_duration()

Example fix

# before
trimmed = TrimVideo.execute(video, start_time=8.0, duration=5.0, strict_duration=True)

# after: clamp to source duration
dur = video.get_duration()
start = min(8.0, max(0.0, dur - 5.0))
trimmed = TrimVideo.execute(video, start_time=start, duration=min(5.0, dur - start), strict_duration=True)

Defensive patterns

Strategy: validation

Validate before calling

dur = video.get_duration()
start_time = max(0.0, min(start_time, dur))
if start_time + duration > dur:
    duration = dur - start_time  # or set strict_duration=False

Try / catch

try:
    out = TrimVideo.execute(video, start_time, duration, True)
except ValueError as e:
    if "Failed to slice" in str(e):
        duration = video.get_duration() - start_time
        out = TrimVideo.execute(video, start_time, duration, False)
    else:
        raise

Prevention

Derive trim windows from get_duration() instead of constants
Prefer strict_duration=False when tail shortening is acceptable

When it happens

Trigger: Requesting start_time + duration beyond the video's end with strict_duration=True (exact length required); start_time >= source duration; NaN/negative duration values; a source whose duration could not be determined so as_trimmed cannot guarantee the slice.

Common situations: Hardcoded trim values reused across videos of different lengths; off-by-one assumptions about inclusive end time; seeking near the tail of a clip with strict duration enforcement on.

Related errors

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/014db56b574a0a3b. Report an issue: GitHub.