SubtitleEdit/subtitleedit · error · InvalidOperationException

OCR engine '{options.OcrEngine}' is not supported. Use one o

Error message

OCR engine '{options.OcrEngine}' is not supported. Use one of: tesseract, nocr, binaryocr, ollama, llamacpp, paddle.

What it means

Thrown by OcrEngineFactory.Create when the requested engine name (after trim + lowercase) matches none of the supported arms in its switch. The factory is the single dispatch point for the `--ocr-engine` CLI option; an unknown name is a user/CLI typo, not a recoverable runtime condition.

Source

Thrown at src/seconv/Core/OcrEngineFactory.cs:21

/// <summary>
/// Creates an <see cref="IOcrEngine"/> from CLI options. Throws with a clear message when
/// the requested engine is unsupported or its prerequisites (binary on PATH, database file)
/// aren't satisfied.
/// </summary>
internal static class OcrEngineFactory
{
    public static IOcrEngine Create(ConversionOptions options)
    {
        var engine = (options.OcrEngine ?? "tesseract").Trim().ToLowerInvariant();
        return engine switch
        {
            "tesseract" or "" => TesseractOcrEngine.Create(options.OcrLanguage),
            "nocr" => new NOcrOcrEngine(ResolveOcrDbPath(options, "nocr", ".nocr")),
            "binaryocr" or "binary" => new BinaryOcrOcrEngine(ResolveOcrDbPath(options, "binaryocr", ".db")),
            "ollama" => new OllamaOcrEngine(options.OllamaUrl, options.OllamaModel, options.OcrLanguage),
            "llamacpp" or "llama.cpp" or "llama" => LlamaCppOcrEngine.Create(options),
            "paddle" or "paddleocr" => PaddleOcrEngine.Create(options.OcrLanguage),
            _ => throw new InvalidOperationException(
                $"OCR engine '{options.OcrEngine}' is not supported. Use one of: tesseract, nocr, binaryocr, ollama, llamacpp, paddle.")
        };
    }

    private static string ResolveOcrDbPath(ConversionOptions options, string engineName, string requiredExtension)
    {
        if (string.IsNullOrWhiteSpace(options.OcrDb))
        {
            var displayExt = requiredExtension.TrimStart('.');
            throw new InvalidOperationException(
                $"{engineName} engine requires --ocr-db=<path-to-Latin{requiredExtension}> (or another {requiredExtension} file). " +
                $"Find them in `%AppData%\\Subtitle Edit\\OCR\\` or download from the SE UI.");
        }
        var path = options.OcrDb;
        if (!path.EndsWith(requiredExtension, StringComparison.OrdinalIgnoreCase))
        {
            path += requiredExtension;
        }

View on GitHub (pinned to 17a9f07487)

Solutions

Use one of the listed engines: tesseract, nocr, binaryocr, ollama, llamacpp, paddle.
Check for trailing whitespace or quotes around the --ocr-engine value.
If using a settings file, ensure the `ocrEngine` key uses a supported value.
Run `seconv --help` to confirm the engine list for your seconv version.

Example fix

// before
seconv in.sup out.srt --ocr-engine tessaract
// after
seconv in.sup out.srt --ocr-engine tesseract

Defensive patterns

Strategy: validation

Validate before calling

static readonly HashSet<string> ValidEngines = new(StringComparer.OrdinalIgnoreCase)
{ "tesseract", "", "nocr", "binaryocr", "binary", "ollama", "llamacpp", "llama.cpp", "llama", "paddle", "paddleocr" };
if (!ValidEngines.Contains(options.OcrEngine ?? "tesseract"))
    throw new ArgumentException("Unsupported OCR engine: " + options.OcrEngine);

Type guard

static bool IsValidOcrEngine(string? e) =>
    ValidEngines.Contains((e ?? "tesseract").Trim().ToLowerInvariant());

Try / catch

try { var engine = OcrEngineFactory.Create(options); }
catch (InvalidOperationException ex) when (ex.Message.Contains("is not supported"))
{
    // print supported list, exit usage error
}

Prevention

Whitelist OCR engine names at CLI parse time.
Document the canonical lower-case names and normalise input casing before dispatch.
Add a unit test enumerating each accepted alias.

When it happens

Trigger: Calling `OcrEngineFactory.Create(options)` with `options.OcrEngine` set to a value outside {tesseract, '', nocr, binaryocr, binary, ollama, llamacpp, llama.cpp, llama, paddle, paddleocr}. Example misspellings: 'tessaract', 'ocr', 'google', 'azure'.

Common situations: Typoing the engine name on the command line; copy-pasting a deprecated engine name from old docs; a wrapper script passing an uppercase or differently-cased name that should still work (it is lowercased, so this is rare).

Related errors

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/3ad1809d22e0a0ee. Report an issue: GitHub.