LykosAI/StabilityMatrix · error · InvalidDataException

Invalid WEBP header

Error message

Invalid WEBP header

What it means

WebpReader.ReadHeader validates the WEBP signature at bytes 8-11 (after the RIFF marker and size field). If those bytes are not 'WEBP' it throws InvalidDataException: the stream is a RIFF container but not a WEBP file (e.g. a WAV or AVI), or the header is corrupt.

Solutions

1. Check bytes 8-11 equal 'WEBP' (and bytes 0-3 equal 'RIFF') before parsing
2. Only feed WebpReader streams known to be actual WEBP files
3. Catch InvalidDataException and classify the file as unsupported
4. Re-download/reconvert the file if it is genuinely meant to be WEBP

Example fix

// before
var animated = new WebpReader(stream).GetIsAnimatedFlag();
// after
var bytes = new byte[12];
stream.ReadExactly(bytes);
stream.Position = 0;
bool isWebp = bytes.AsSpan(0, 4).SequenceEqual("RIFF"u8)
           && bytes.AsSpan(8, 4).SequenceEqual("WEBP"u8);
var animated = isWebp ? new WebpReader(stream).GetIsAnimatedFlag() : false;

byte[] head = new byte[12];
using (var fs = File.OpenRead(path)) { if (fs.Length < 12) return false; fs.ReadExactly(head); }
bool isWebp = head.AsSpan(0,4).SequenceEqual("RIFF"u8) && head.AsSpan(8,4).SequenceEqual("WEBP"u8);

static bool IsWebpFile(Stream s) { var b = new byte[12]; long pos = s.Position; if (s.Length - pos < 12) return false; s.ReadExactly(b); s.Position = pos; return b.AsSpan(0,4).SequenceEqual("RIFF"u8) && b.AsSpan(8,4).SequenceEqual("WEBP"u8); }

try { animated = new WebpReader(stream).GetIsAnimatedFlag(); }
catch (InvalidDataException ex) { Logger.Debug("Not a WEBP: {Msg}", ex.Message); animated = false; }

When it happens

Trigger: Calling GetIsAnimatedFlag on a non-WEBP RIFF file (WAV/AVI), a file with a corrupted or tampered header, or a stream shorter than 12 bytes so the WEBP read pulls garbage.

Common situations: Files renamed to .webp without conversion; truncated downloads where the size field parsed but format bytes are wrong; batch metadata scans over mixed image/audio directories.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Invalid RIFF header
• Fields line not found
• Unable to locate starting marker of last line
• Invalid Token
• Service type is not assignable to

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/98e0bbda12c26105. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Helper/Webp/WebpReader.cs:40

    }

    private void ReadHeader()
    {
        // RIFF
        var riff = ReadBytes(4);
        if (!riff.SequenceEqual([.."RIFF"u8]))
        {
            throw new InvalidDataException("Invalid RIFF header");
        }

        // Size: uint32
        headerFileSize = ReadUInt32();

        // WEBP
        var webp = ReadBytes(4);
        if (!webp.SequenceEqual([.."WEBP"u8]))
        {
            throw new InvalidDataException("Invalid WEBP header");
        }
    }

    // Read a single chunk and discard its contents
    private string ReadVoidChunk()
    {
        // FourCC: 4 bytes in ASCII
        var result = ReadBytes(4);

        // Size: uint32
        var size = ReadUInt32();

        BaseStream.Seek(size, SeekOrigin.Current);

        return Encoding.ASCII.GetString(result);
    }
}

View on GitHub (pinned to af93d6ef57)