feat(subtitles): add local Japanese subtitle generation (#240)

src/core/services/subtitle-generation-models.ts

@@ -0,0 +1,90 @@
+import { access, open, stat } from 'node:fs/promises';
+import { constants } from 'node:fs';
+import path from 'node:path';
+import { getSubtitleGenerationModel } from '../../shared/subtitle-generation-model-catalog';
+import { expandSubtitleGenerationPath } from './subtitle-generation-files';
+import { downloadSubtitleGenerationArtifact } from './subtitle-generation-download';
+import type {
+  SubtitleGenerationConfig,
+  SubtitleGenerationModelStatus,
+  SubtitleGenerationProgress,
+} from '../../shared/subtitle-generation';
+
+export function isMissingFile(error: unknown): boolean {
+  return error instanceof Error && 'code' in error && error.code === 'ENOENT';
+}
+
+async function modelCompatibilityError(modelPath: string): Promise<string | undefined> {
+  const file = await open(modelPath, 'r');
+  try {
+    // whisper_model_load reads GGML magic, then n_vocab. is_multilingual uses n_vocab >= 51865.
+    const header = Buffer.alloc(8);
+    const { bytesRead } = await file.read(header, 0, header.length, 0);
+    if (
+      bytesRead !== header.length ||
+      header.readUInt32LE(0) !== 0x67676d6c ||
+      header.readInt32LE(4) <= 0
+    ) {
+      return 'Unsupported model format. Choose a whisper.cpp GGML .bin model.';
+    }
+    if (header.readInt32LE(4) < 51865) {
+      return 'This Whisper model is English-only. Japanese subtitle generation requires a multilingual model.';
+    }
+    return undefined;
+  } finally {
+    await file.close();
+  }
+}
+
+export async function resolveSubtitleGenerationModel(
+  config: SubtitleGenerationConfig,
+  modelDirectory: string,
+): Promise<SubtitleGenerationModelStatus> {
+  const external = config.modelPath.trim();
+  const modelPath = external
+    ? path.resolve(expandSubtitleGenerationPath(external))
+    : path.resolve(modelDirectory, `ggml-${config.managedModel}.bin`);
+  try {
+    const info = await stat(modelPath);
+    if (!info.isFile() || info.size === 0) {
+      return { kind: 'invalid', path: modelPath, message: 'Model must be a nonempty file.' };
+    }
+    await access(modelPath, constants.R_OK);
+    if (!external && info.size !== getSubtitleGenerationModel(config.managedModel).size) {
+      return { kind: 'invalid', path: modelPath, message: 'Managed model has an unexpected size.' };
+    }
+    const compatibilityError = await modelCompatibilityError(modelPath);
+    if (compatibilityError)
+      return { kind: 'invalid', path: modelPath, message: compatibilityError };
+    return { kind: external ? 'external' : 'managed', path: modelPath };
+  } catch (error) {
+    if (!external && isMissingFile(error)) return { kind: 'missing', path: modelPath };
+    return {
+      kind: 'invalid',
+      path: modelPath,
+      message: `Cannot read model: ${error instanceof Error ? error.message : String(error)}`,
+    };
+  }
+}
+
+export async function downloadSubtitleGenerationModel(input: {
+  config: SubtitleGenerationConfig;
+  modelDirectory: string;
+  onProgress?: (progress: SubtitleGenerationProgress) => void;
+  signal?: AbortSignal;
+}): Promise<string> {
+  input.signal?.throwIfAborted();
+  const current = await resolveSubtitleGenerationModel(input.config, input.modelDirectory);
+  if (current.kind === 'external' || current.kind === 'managed') return current.path;
+  if (current.kind === 'invalid') throw new Error(current.message);
+  const model = getSubtitleGenerationModel(input.config.managedModel);
+  return downloadSubtitleGenerationArtifact({
+    url: `https://huggingface.co/ggerganov/whisper.cpp/resolve/5359861c739e955e79d9a303bcbc70fb988958b1/ggml-${input.config.managedModel}.bin`,
+    size: model.size,
+    sha256: model.sha256,
+    destination: current.path,
+    label: 'Whisper model',
+    onProgress: input.onProgress,
+    signal: input.signal,
+  });
+}