remotion-dev/remotion · error

language must be a non-empty string.

Error message

language must be a non-empty string.

What it means

Validation inside the WebMcp transcription tool. The language parameter (defaulting to 'en') must be a non-empty string after input coercion; an empty, null-like, or non-string language value is rejected before transcription begins. This is an input-validation guard on the caller-supplied language field.

Source

Thrown at packages/studio/src/components/WebMcp.tsx:535

						const model = whisper
							.getAvailableModels()
							.find((candidate) => candidate.name === modelName);
						if (!model) {
							throw new Error(`Unknown Whisper model: ${modelName}.`);
						}

						const task = input.task ?? 'transcribe';
						if (task !== 'transcribe' && task !== 'translate') {
							throw new Error('task must be transcribe or translate.');
						}

						if (task === 'translate' && !model.supportsTranslation) {
							throw new Error(`${model.name} does not support translation.`);
						}

						const language = input.language ?? 'en';
						if (typeof language !== 'string' || language.length === 0) {
							throw new Error('language must be a non-empty string.');
						}

						const chunkLengthInSeconds = input.chunkLengthInSeconds ?? 30;
						const strideLengthInSeconds = input.strideLengthInSeconds ?? 5;
						const temperature = input.temperature ?? 1;
						const topK = input.topK ?? 50;
						const repetitionPenalty = input.repetitionPenalty ?? 1;
						const noRepeatNgramSize = input.noRepeatNgramSize ?? 0;
						if (
							typeof chunkLengthInSeconds !== 'number' ||
							!Number.isFinite(chunkLengthInSeconds) ||
							chunkLengthInSeconds < 1 ||
							chunkLengthInSeconds > 30
						) {
							throw new Error('chunkLengthInSeconds must be between 1 and 30.');
						}

						if (

View on GitHub (pinned to b2f4e34732)

Solutions

1. Omit input.language to use the default "en"
2. Pass a non-empty language code string such as "en", "de", "zh"
3. Trim whitespace before sending to avoid effectively empty values

Example fix

// before
{ "language": "" }
// after
{ "language": "de" } // or omit to default to "en"

if (input.language !== undefined && (typeof input.language !== 'string' || input.language.trim() === '')) {
  throw new Error('language must be a non-empty string');
}

const isValidLanguage = (v: unknown): v is string =>
  typeof v === 'string' && v.length > 0;

try {
  await callWhisperTool({ language: input.language });
} catch (err) {
  if (err instanceof Error && err.message.startsWith('language must be')) {
    delete input.language; // use default 'en'
  }
}

When it happens

Trigger: Passing input.language as "", null combined with explicit undefined handling, a number, an array, or any non-string value.

Common situations: Clearing a language field in a UI and submitting an empty string; passing a locale object instead of an ISO-639-1 code string.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• forceFullSequences and doSample must be booleans.
• "${name}" must be a [number, number] tuple
• Invalid whisper model ${model}. Available: ${models.join(',
• outputRange tuples must contain only finite numbers, but got
• ${name} must contain only numbers

AI-assisted analysis of remotion-dev/remotion@b2f4e34732 (2026-09-09). Data as JSON: /api/errors/f67680f85882bba5. Report an issue: GitHub.