SubtitleEdit/subtitleedit · error · InvalidOperationException

Translate engine ' ' is not supported. Use one of: .

Error message

Translate engine '{options.TranslateEngine}' is not supported. Use one of: {string.Join(", ", SupportedEngines)}.

What it means

InvalidOperationException from the engine-name switch in AutoTranslateRunner: the value of options.TranslateEngine did not match any case (the supported set like 'libretranslate', 'nllb-serve', 'nllb-api', 'llamacpp', etc.). The message lists SupportedEngines so the user sees the accepted values.

Solutions

Print SupportedEngines (it is in the error message) and use one of those exact strings.
If you need a deprecated engine, check the runner's SupportedEngines constant for the canonical name.
Normalize input: trim and lowercase the engine name before the switch.

Example fix

// before
default:
    throw new InvalidOperationException($"Translate engine '{options.TranslateEngine}' is not supported. Use one of: {string.Join(", ", SupportedEngines)}.");

// after — case-insensitive dispatch so 'LLAMACPP' matches
var key = (options.TranslateEngine ?? string.Empty).Trim().ToLowerInvariant();
switch (key) { /* ... */ default: throw new InvalidOperationException(...); }

Defensive patterns

Strategy: validation

Validate before calling

if (!SupportedEngines.Contains((options.TranslateEngine ?? "").Trim(), StringComparer.OrdinalIgnoreCase))
    throw new InvalidOperationException($"Unsupported engine. Valid: {string.Join(", ", SupportedEngines)}");

Type guard

static bool IsSupportedEngine(string? name) => name != null && SupportedEngines.Contains(name.Trim(), StringComparer.OrdinalIgnoreCase);

Try / catch

null

Prevention

Validate the engine name against SupportedEngines before constructing the runner.
Normalize (trim + lowercase) the CLI input at parse time.
Document supported engine strings in --help.

When it happens

Trigger: Invoking the runner with a TranslateEngine string not present in SupportedEngines — typo, wrong casing, deprecated name, or a custom value the switch does not know.

Common situations: CLI flag --translate-engine misspelled ('llama' instead of 'llamacpp'); pipeline upgraded and an old engine name was removed; case sensitivity ('NLLB' vs 'nllb-api').

Related errors

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/67f8c433bbd15c43. Report an issue: GitHub.

Appendix: source

Thrown at src/seconv/Core/AutoTranslateRunner.cs:113

                    tools.AutoTranslateLibreUrl = url;
                }
                break;
            case "nllb-serve":
                translator = new NoLanguageLeftBehindServe();
                if (!string.IsNullOrEmpty(url))
                {
                    tools.AutoTranslateNllbServeUrl = url;
                }
                break;
            case "nllb-api":
                translator = new NoLanguageLeftBehindApi();
                if (!string.IsNullOrEmpty(url))
                {
                    tools.AutoTranslateNllbApiUrl = url;
                }
                break;
            default:
                throw new InvalidOperationException(
                    $"Translate engine '{options.TranslateEngine}' is not supported. Use one of: {string.Join(", ", SupportedEngines)}.");
        }

        return new AutoTranslateRunner(options, translator, llamaCppModel);
    }

    /// <summary>
    /// Translates all paragraphs in place. Reuses the already-running llama-server across
    /// files in the same run (the server manager is a no-op when the model matches).
    /// </summary>
    public async Task TranslateAsync(Subtitle subtitle, CancellationToken cancellationToken)
    {
        if (_llamaCppModel != null && !LlamaCppServerManager.IsServerRunning)
        {
            if (!_options.Quiet)
            {
                Console.WriteLine($"  Starting llama-server with model {Path.GetFileName(_llamaCppModel.FileName)} (stops at exit)...");
            }

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