remotion-dev/remotion · error · Error

`webFileReader` cannot create adjacent file sources.

Error message

`webFileReader` cannot create adjacent file sources.

What it means

Thrown unconditionally by webFileCreateAdjacentFileSource. The webFileReader cannot resolve adjacent file sources because a File/Blob has no associated base URL or directory; only the single blob is available. Any attempt to compute a companion resource path under this reader fails by design.

Source

Thrown at packages/media-parser/src/readers/from-web-file.ts:57

				} catch {}

				return Promise.resolve();
			},
		},
		contentLength: src.size,
		name: src instanceof File ? src.name : src.toString(),
		supportsContentRange: true,
		contentType: src.type,
		needsContentRange: true,
	});
};

export const webFileReadWholeAsText: ReadWholeAsText = () => {
	throw new Error('`webFileReader` cannot read auxiliary files.');
};

export const webFileCreateAdjacentFileSource: CreateAdjacentFileSource = () => {
	throw new Error('`webFileReader` cannot create adjacent file sources.');
};

export const webFileReader: MediaParserReaderInterface = {
	read: webFileReadContent,
	readWholeAsText: webFileReadWholeAsText,
	createAdjacentFileSource: webFileCreateAdjacentFileSource,
	preload: () => {
		// doing nothing, it's just for when fetching over the network
	},
};

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Use fetchReader with the media's URL so adjacent sources can be resolved relative to that URL.
2. On the server, use nodeReader so adjacent files resolve relative to dirname(src).
3. Re-encode the media to be self-contained (inline tracks/moov) so no adjacent source is needed.

Example fix

// before
await parseMedia({ src: fileBlob, fields: {...} }); // needs adjacent file

// after
await parseMedia({ src: mediaUrl, srcType: 'fetch', fields: {...} });

// webFileReader cannot create adjacent sources - pre-check container needs
if (needsAdjacentSources(format) && src instanceof Blob) throw new TypeError('webFileReader cannot create adjacent sources; use fetchReader');

const readerSupportsAdjacent = (reader: string) => reader !== 'web-file';

try { await parseMedia({ src: file, fields }); } catch (e) { if (/cannot create adjacent file sources/.test(String((e as Error).message))) { await parseMedia({ src: url, srcType: 'fetch', fields }); } else throw e; }

When it happens

Trigger: Parsing with webFileReader when the container format requests an adjacent/external file source (e.g. external moov atom, alternate track, sidecar asset). createAdjacentFileSource is invoked and always throws.

Common situations: Browser upload-and-parse flows where the container references external assets. Moov-relocation or fragmented-mp4 variants that point to sibling files. Using webFileReader for a media type that fundamentally needs companion files.

Related errors

• `webFileReader` cannot read auxiliary files.
• `inputTypeFileReader` only supports `File` objects
• Not enough bytes left to parse EBML - this should not happen
• has no bytes
• `reader` should not be provided to `${apiName}`. If you want

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/99278ed3d189917c. Report an issue: GitHub.