unslothai/unsloth · error · ValueError

A reference decoded to no data.

Error message

A reference decoded to no data.

What it means

The reference payload was syntactically valid base64 but decoded to zero bytes (e.g. the empty string is technically valid base64). _decode_b64_media treats a zero-length blob as an error distinct from 'invalid base64' and from 'empty input', catching data URLs like 'data:image/png;base64,' whose payload part is blank.

Source

Thrown at studio/backend/core/inference/video.py:423

_MAX_REFERENCE_MEDIA_BYTES = 96 * 1024 * 1024


def _decode_b64_media(data: Optional[str]) -> bytes:
    """Decode a base64 media payload, optionally wrapped in a data URL."""
    import base64
    import binascii

    raw = (data or "").strip()
    if not raw:
        raise ValueError("A reference was sent empty.")
    if raw.startswith("data:"):
        _, _, raw = raw.partition(",")
    try:
        blob = base64.b64decode(raw, validate = False)
    except (binascii.Error, ValueError) as exc:
        raise ValueError(f"Invalid base64 media data: {exc}") from exc
    if not blob:
        raise ValueError("A reference decoded to no data.")
    if len(blob) > _MAX_REFERENCE_MEDIA_BYTES:
        raise ValueError(
            f"A reference is too large ({len(blob) / 1e6:.0f} MB); the limit is "
            f"{_MAX_REFERENCE_MEDIA_BYTES / 1e6:.0f} MB."
        )
    return blob


class _VideoGenerationCancelled(Exception):
    """Unwinds a denoise loop that has no cooperative interrupt (no step callback);
    generate() maps it to the VIDEO_CANCELLED_MSG sentinel the routes 409 on."""


@contextlib.contextmanager
def _scheduler_step_progress(pipe: Any, on_step: Any):
    """Progress + cancellation for pipelines WITHOUT callback_on_step_end.

    HunyuanVideo15Pipeline exposes no per-step callback, but every denoise step

View on GitHub (pinned to 203007d190)

Solutions

1. Ensure the media blob is actually read and non-empty before encoding it.
2. Skip sending the reference entirely when the source file/blob is zero-length.
3. If the field is optional, omit the key rather than sending an empty wrapper.

Example fix

# before
ref = f'data:image/png;base64,{b64}'  # b64 == '' for a missing file

# after
ref = f'data:image/png;base64,{b64}' if b64 else None
# and omit the field when ref is None

import base64

def decodes_to_data(ref: str | None) -> bool:
    if not ref or not ref.strip():
        return False
    raw = ref.strip()
    if raw.startswith('data:'):
        raw = raw.partition(',')[2]
    try:
        return len(base64.b64decode(raw)) > 0
    except Exception:
        return False

def nonempty_b64_payload(value: str) -> bool:
    raw = value.strip()
    if raw.startswith('data:'):
        raw = raw.partition(',')[2]
    return len(raw) > 0 and base64.b64decode(raw, validate=False) != b''

try:
    blob = _decode_b64_media(ref)
except ValueError as e:
    if 'decoded to no data' in str(e):
        ref = capture_fallback_or_none()  # re-capture the source media
    else:
        raise

When it happens

Trigger: Sending a data URL whose comma-separated payload is empty, or a bare base64 of b'' (empty string). The earlier empty check only fires on whitespace-only input, so a well-formed wrapper around nothing reaches this branch.

Common situations: A UI that always emits the data-URL wrapper even for a missing file; canvas/ImageBlob.toDataURL() on an unrendered element; a truncated upload where the encoder produced the header but no body.

Related errors

• each reference must be at most 32 MiB (base64)
• A reference was sent empty.
• Invalid base64 media data: {exc}
• Invalid base64 image data: {exc}
• Unknown model_kind '{model_kind}'. Expected one of {sorted(_

AI-assisted analysis of unslothai/unsloth@203007d190 (2026-08-15). Data as JSON: /api/errors/fc1573319a89d36e. Report an issue: GitHub.