SubtitleEdit/subtitleedit · error · RiffParserException

Element size mismatch for element {FromFourCc(fourCc)} need

Error message

Element size mismatch for element {FromFourCc(fourCc)} need {size} but have only {bytesleft}

What it means

While descending the RIFF tree, RiffParser computed the remaining bytes in the current scope, then compared them to the chunk/list size just read. If the declared size exceeds the bytes remaining, the data is inconsistent; the parser skips the remaining bytes (to resync) and throws RiffParserException. This is the canonical 'file lies about chunk size' guard.

Source

Thrown at src/libse/ContainerFormats/RiffParser.cs:240

                return false;
            }

            // We have enough bytes, read
            int fourCc;
            int size;

            ReadTwoInts(out fourCc, out size);

            // Reduce bytes left
            bytesleft -= TwoDWordSize;

            // Do we have enough bytes?
            if (bytesleft < size)
            {
                // Skip the bad data and throw an exception
                SkipData(bytesleft);
                bytesleft = 0;
                throw new RiffParserException("Element size mismatch for element " + FromFourCc(fourCc)
                + " need " + size + " but have only " + bytesleft);
            }

            // Examine the element, is it a list or a chunk
            string type = FromFourCc(fourCc);
            if (type == List4Cc)
            {
                // We have a list
                ReadOneInt(out fourCc);

                if (null == list)
                {
                    SkipData(size - 4);
                }
                else
                {
                    // Invoke the list method
                    list(this, fourCc, size - 4);

View on GitHub (pinned to 17a9f07487)

Solutions

1. Re-acquire the file from source; an inconsistent RIFF tree cannot be safely parsed.
2. Catch RiffParserException at the format-detection level and try alternate container formats.
3. Pre-validate by reading the top-level RIFF size and comparing to file length.
4. Use a tolerant parser that skips the bad chunk if salvage is required.

Example fix

// before
if (bytesleft < size) { SkipData(bytesleft); bytesleft = 0; throw new RiffParserException("Element size mismatch..."); }

// after
if (bytesleft < size) { SkipData(bytesleft); bytesleft = 0; throw new RiffParserException($"Element {FromFourCc(fourCc)} declared {size}B but only {bytesleft}B remain in scope"); }

if (size > bytesleft) throw new InvalidDataException($"Chunk {FromFourCc(fourCc)} size {size} exceeds remaining {bytesleft}");

try { rp.ReadElement(...); }
catch (RiffParserException ex) when (ex.Message.Contains("size mismatch")) { /* corrupt RIFF; abort */ }

When it happens

Trigger: A RIFF chunk/list declares a size larger than the enclosing scope; nested LIST size inconsistent with parent; truncated file where the final chunk's size header was written but data was cut.

Common situations: AVI/WAV produced by a buggy muxer; file partially overwritten; concatenated RIFF fragments without size fixup.

Related errors

• Problem reading AVI header.
• Unable to read. Corrupt RIFF file {FileName}
• Problem accessing RIFF file {FileName}
• Problem seeking in file {FileName}
• Problem reading data in file {FileName}

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/d0ed3baafad48b4b. Report an issue: GitHub.