Bilibili 下载助手 (Bilibili Download Helper)

A Chrome/Edge extension that downloads videos from bilibili.com — including copyright-restricted 番剧 (anime), movies, and TV dramas that can be watched but not cached offline. Built with SvelteKit, Svelte 5, Skeleton 3, Tailwind 4, and Vite.

Built from the SvelteKit Chrome Extension template by Luke Hagar.

Features

• Downloads UGC videos (/video/BV...) and bangumi episodes (/bangumi/play/ep...)
• Fetches separate DASH audio + video streams and merges them with in-browser WASM FFmpeg
• WBI-signed playurl requests (required by Bilibili's current API)
• Automatic quality selection from the Bilibili player
• Normal mode (browser default download) and Advanced mode (auto-merge + rename)

Stack

• Svelte 5 (runes), Skeleton 3, Tailwind 4
• TypeScript, Zod schemas
• @ffmpeg/ffmpeg (WASM) for audio/video merging
• Vitest for unit tests
• Bun as the package manager

Developing

bun install
bun run dev

Building

Content scripts are built separately from the SvelteKit extension because they run in Bilibili's page context (injected via a seed script).

# Build content scripts only (outputs to static/)
bun run build:content

# Build the SvelteKit extension (outputs to build/)
bun run build

# Build everything in the right order
bun run build:all

Load build/ as an unpacked Chrome extension — see Extension Development Basics.

Testing

bun run test:unit   # vitest unit tests

Tests live alongside their modules in src/lib/*.test.ts. The WBI signing module (src/lib/wbi.test.ts) verifies the documented Bilibili mixin-key and w_rid test vectors.

Architecture

Path	Purpose
src/routes/	SvelteKit pages (extension popup/options)
src/content-script/seed.ts	Isolated-world MV3 content script — injects main.ts into the page
src/content-script/main.ts	Page-world logic: XHR interception, page-state parsing, playurl fetch, UI render
src/lib/wbi.ts	WBI parameter signing (mixin key + w_rid/wts)
src/lib/bilibili-api.ts	UGC + bangumi playurl API clients
src/lib/download.ts	Normal + advanced (merge) download flows
src/lib/ffmpeg.ts	WASM FFmpeg audio/video merge
src/lib/host.ts	Shadow-DOM helper UI
src/lib/schemas.ts	Zod schemas (DashData, DurlSegment, ErrorCode, etc.)
vite.content.config.ts	Vite config for the content-script bundle
tsconfig.content.json	Standalone tsconfig for content-script type-checking
static/manifest.json	MV3 manifest
build/	Built extension output (load as unpacked)

See AGENTS.md for the full agent development guide.