SubtitleEdit/subtitleedit · error · FileNotFoundException

nOCR database not found

Error message

nOCR database not found: {nOcrDbPath}. Use --ocr-db to point to a .nocr file (typically %AppData%\Subtitle Edit\OCR\Latin.nocr or similar).

What it means

Thrown by the NOcrOcrEngine constructor when the supplied nOCR database path does not exist on disk. nOCR is a lightweight, image-template OCR engine bundled with Subtitle Edit that needs a prebuilt .nocr database file to recognize glyphs. Without that file the engine has no character definitions and cannot function, so construction fails fast rather than producing garbage output.

Solutions

Supply a valid .nocr file via `--ocr-db=/path/to/Latin.nocr`.
Download or copy `Latin.nocr` from a Subtitle Edit installation (GUI: Options -> Settings -> OCR) into the project and point --ocr-db at it.
If you do not need nOCR, switch engines with `--ocr-engine tesseract` (default, no db required).
Verify the path resolves from the working directory seconv runs in; use an absolute path to remove ambiguity.

Example fix

// before
seconv in.sup out.srt --ocr-engine nocr
// after
seconv in.sup out.srt --ocr-engine nocr --ocr-db=/home/user/SE/OCR/Latin.nocr

Defensive patterns

Strategy: validation

Validate before calling

string db = options.OcrDb;
if (options.OcrEngine == "nocr")
{
    if (string.IsNullOrWhiteSpace(db))
        throw new InvalidOperationException("--ocr-db is required for nocr");
    if (!File.Exists(db.EndsWith(".nocr", StringComparison.OrdinalIgnoreCase) ? db : db + ".nocr"))
        throw new FileNotFoundException("nOCR db not found: " + db);
}

Type guard

static bool IsNocrDbReady(string? path) =>
    !string.IsNullOrWhiteSpace(path) && File.Exists(path) && path.EndsWith(".nocr", StringComparison.OrdinalIgnoreCase);

Try / catch

try { var engine = new NOcrOcrEngine(dbPath); }
catch (FileNotFoundException ex) when (ex.FileName == dbPath)
{
    // report missing db, prompt user for path, abort this input
}

Prevention

Validate --ocr-db with File.Exists before constructing the engine.
Ship a known-good Latin.nocr with your deployment and reference it by absolute path.
Fail fast in CLI arg parsing: if engine is nocr, require a non-empty --ocr-db.

When it happens

Trigger: Constructing `new NOcrOcrEngine(nOcrDbPath)` (directly, or via OcrEngineFactory when `--ocr-engine nocr` is passed) with a path that fails `File.Exists`. Also triggered if `ResolveOcrDbPath` appends `.nocr` to a base path whose full form does not exist.

Common situations: Passing `--ocr-engine nocr` without `--ocr-db`; typoing the db path; the file living under `%AppData%\Subtitle Edit\OCR\Latin.nocr` which is absent on a fresh non-Windows install; copying a project to a machine that never had the Subtitle Edit GUI install its OCR assets.

Related errors

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/de35f2e2c4d3cdc0. Report an issue: GitHub.

Appendix: source

Thrown at src/seconv/Core/NOcrOcrEngine.cs:23

/// <summary>
/// In-process OCR via Subtitle Edit's nOCR matcher. Requires a <c>.nocr</c> database file
/// (typically shipped with SE under <c>%AppData%\Subtitle Edit\OCR\</c>; pass the path
/// via <c>--ocr-db</c>).
/// </summary>
internal sealed class NOcrOcrEngine : IOcrEngine
{
    public string Name => "nocr";
    private readonly NOcrDb _db;
    private readonly NOcrCaseFixer _caseFixer = new();
    private const int MaxWrongPixels = 25;
    private const int PixelsAreSpaceDefault = 12;

    public NOcrOcrEngine(string nOcrDbPath)
    {
        if (!File.Exists(nOcrDbPath))
        {
            throw new FileNotFoundException(
                $"nOCR database not found: {nOcrDbPath}. Use --ocr-db to point to a .nocr file " +
                "(typically %AppData%\\Subtitle Edit\\OCR\\Latin.nocr or similar).", nOcrDbPath);
        }
        _db = new NOcrDb(nOcrDbPath);
        if (_db.TotalCharacterCount == 0)
        {
            throw new InvalidOperationException($"nOCR database is empty: {nOcrDbPath}");
        }
    }

    public string Recognize(SKBitmap bitmap)
    {
        if (bitmap is null || bitmap.Width == 0 || bitmap.Height == 0)
        {
            return string.Empty;
        }

        var parent = new NikseBitmap2(bitmap);

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