SubtitleEdit/subtitleedit · error · InvalidOperationException

File is not a valid MCC subtitle: {filePath}

Error message

File is not a valid MCC subtitle: {filePath}

What it means

Thrown by LoadMcc when MacCaption10.IsMine(null, filePath) returns false — the file's content does not match the MacCaption (MCC, SCTE-104 caption) format signature. The .mcc extension alone is not trusted; the format sniffer must recognise the header.

Source

Thrown at src/seconv/Core/ContainerSubtitleLoader.cs:388

            subtitle.Paragraphs.AddRange(paragraphs);
            subtitle.Renumber();
            var lang = LanguageAutoDetect.AutoDetectGoogleLanguageOrNull(subtitle) ?? string.Empty;
            tracks.Add(new LoadedTrack(subtitle, new SubRip(), lang, trackId));
        }

        if (tracks.Count == 0)
        {
            throw new InvalidOperationException($"No subtitle tracks in MP4 file: {filePath}");
        }
        return tracks;
    }

    private static List<LoadedTrack> LoadMcc(string filePath)
    {
        var mcc = new MacCaption10();
        if (!mcc.IsMine(null, filePath))
        {
            throw new InvalidOperationException($"File is not a valid MCC subtitle: {filePath}");
        }
        var subtitle = new Subtitle();
        mcc.LoadSubtitle(subtitle, null, filePath);
        subtitle.Renumber();
        return [new LoadedTrack(subtitle, mcc, string.Empty, null)];
    }

    private static List<LoadedTrack> LoadBluRaySup(string filePath, ConversionOptions options)
    {
        var subtitle = ImageOcrLoader.LoadBluRaySup(filePath, options);
        if (subtitle.Paragraphs.Count == 0)
        {
            throw new InvalidOperationException($"No subtitles recognised in Blu-Ray sup file: {filePath}");
        }
        return [new LoadedTrack(subtitle, new SubRip(), string.Empty, null)];
    }

    private static List<LoadedTrack> LoadVobSub(string subPath, string idxPath, ConversionOptions options)

View on GitHub (pinned to 17a9f07487)

Solutions

1. Open the file in a text editor and verify it starts with the MCC header (e.g. 'SCC_Caption' / FILE_FORMAT markers).
2. If it is a different caption format (SCC, SRT), rename it correctly so the loader routes to the right parser.
3. Re-export the MCC from the original captioning tool if it is corrupt.

// Use the format sniffer directly before the loader.
var mcc = new MacCaption10();
if (!mcc.IsMine(null, filePath))
    return Error($"Not an MCC file: {filePath}");

try { tracks = ContainerSubtitleLoader.TryLoadTracks(filePath, options); }
catch (InvalidOperationException ex) when (ex.Message.Contains("valid MCC subtitle"))
{ Console.Error.WriteLine(ex.Message); return; }

When it happens

Trigger: Passing a .mcc path whose contents are not a real MacCaption 1.0 file (ContainerSubtitleLoader.cs:386). The IsMine check inspects the file header/magic; a mismatch triggers the throw before any parsing.

Common situations: A non-MCC file given a .mcc extension; a truncated/garbled MCC; an MCC in an unsupported variant the sniffer rejects; a file that is actually another caption format (e.g. SCC) mis-named.

Related errors

• Unable to access bitmap pixel data.
• Too many bytes for CCData!
• Dvd language {code} not found!
• NameList: Unable to read name list file: {fileNameOrUrl}
• No VobSub subtitles in MKV track #{track.TrackNumber}.

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/ec74568206fcd19f. Report an issue: GitHub.