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

src/core/services/subtitle-generation-vad-model.ts

@@ -0,0 +1,63 @@
+import { access, stat } from 'node:fs/promises';
+import { constants } from 'node:fs';
+import path from 'node:path';
+import type {
+  SubtitleGenerationConfig,
+  SubtitleGenerationModelStatus,
+  SubtitleGenerationProgress,
+} from '../../shared/subtitle-generation';
+import { SUBTITLE_GENERATION_VAD_MODEL } from '../../shared/subtitle-generation-vad-model';
+import { expandSubtitleGenerationPath } from './subtitle-generation-files';
+import { isMissingFile } from './subtitle-generation-models';
+import { downloadSubtitleGenerationArtifact } from './subtitle-generation-download';
+
+export async function resolveSubtitleGenerationVadModel(
+  config: SubtitleGenerationConfig,
+  modelDirectory: string,
+): Promise<SubtitleGenerationModelStatus> {
+  const external = config.vadModelPath.trim();
+  const modelPath = external
+    ? path.resolve(expandSubtitleGenerationPath(external))
+    : path.resolve(modelDirectory, SUBTITLE_GENERATION_VAD_MODEL.filename);
+  try {
+    const info = await stat(modelPath);
+    if (
+      !info.isFile() ||
+      info.size === 0 ||
+      (!external && info.size !== SUBTITLE_GENERATION_VAD_MODEL.size)
+    )
+      return {
+        kind: 'invalid',
+        path: modelPath,
+        message: 'Speech detection model has an invalid size.',
+      };
+    await access(modelPath, constants.R_OK);
+    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 speech detection model: ${error instanceof Error ? error.message : String(error)}`,
+    };
+  }
+}
+
+export async function downloadSubtitleGenerationVadModel(input: {
+  config: SubtitleGenerationConfig;
+  modelDirectory: string;
+  onProgress?: (progress: SubtitleGenerationProgress) => void;
+  signal?: AbortSignal;
+}): Promise<string> {
+  input.signal?.throwIfAborted();
+  const current = await resolveSubtitleGenerationVadModel(input.config, input.modelDirectory);
+  if (current.kind === 'invalid') throw new Error(current.message);
+  if (current.kind !== 'missing') return current.path;
+  return downloadSubtitleGenerationArtifact({
+    ...SUBTITLE_GENERATION_VAD_MODEL,
+    destination: current.path,
+    label: 'Silero speech detection model',
+    onProgress: input.onProgress,
+    signal: input.signal,
+  });
+}