fix(bilibili): keep long videos playing when the CDN drops the stream (#161)

Long B站 videos (2-3 h) still stopped ~15-20 min in, the same symptom as
#89. Reconnecting to the same URL is not enough once the CDN session is
gone, so:

- Prefer an upos/cos mirror from baseUrl + backupUrl over PCDN hosts
  (*.mcdn.bilivideo.cn, *.szbdyd.com), which are the ones that cut off.
- When a B站 track ends more than 30 s before its known duration, fetch
  a fresh URL and resume at the current position instead of advancing.
  Up to 3 attempts without real progress, then advance as before; a
  track the user started meanwhile is never clobbered.
- Seek B站 URLs input-side (-ss before -i). Their CDN serves Range, so a
  resume jumps to the byte offset instead of re-downloading everything
  before it (measured locally: 0.2 s vs a full-file download at 1.5 h
  into a 2 h fMP4), which would otherwise trip the 60 s stall watchdog.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/audio/player.test.ts

@@ -64,6 +64,14 @@ describe("buildFfmpegArgs", () => {
     expect(ssIdx).toBeGreaterThan(iIdx);
   });
 
+  it("seeks B站 streams input-side (before -i) so a resume jumps via Range instead of re-downloading (#161)", () => {
+    const args = buildFfmpegArgs("https://upos-sz-mirrorcos.bilivideo.com/audio.m4s", 3600);
+    const ssIdx = args.indexOf("-ss");
+    expect(args[ssIdx + 1]).toBe("3600");
+    expect(ssIdx).toBeLessThan(args.indexOf("-i"));
+    expect(args.lastIndexOf("-ss")).toBe(ssIdx); // only one -ss
+  });
+
   it("does not insert -ss when seekSeconds is 0", () => {
     const args = buildFfmpegArgs("https://example.com/song.mp3", 0);
     expect(args).not.toContain("-ss");

src/audio/player.ts

@@ -76,8 +76,9 @@ export function cleanupTempDir(dir: string): void {
 export function buildFfmpegArgs(url: string, seekSeconds: number): string[] {
   const args: string[] = [];
   const isHttp = /^https?:\/\//i.test(url);
+  const isBilibili = isHttp && (url.includes("bilivideo") || url.includes("bilibili"));
 
-  if (isHttp && (url.includes("bilivideo") || url.includes("bilibili"))) {
+  if (isBilibili) {
     args.push(
       "-headers",
       `Referer: https://www.bilibili.com\r\nUser-Agent: ${BROWSER_UA}\r\n`,
@@ -103,9 +104,15 @@ export function buildFfmpegArgs(url: string, seekSeconds: number): string[] {
       "-reconnect_on_http_error", "4xx,5xx",
     );
   }
+  // B站's CDN serves Range requests, so seek input-side: FFmpeg jumps straight
+  // to the byte offset. Output-side seek would download and decode everything
+  // before the target first — minutes for a resume deep into a 3-hour video
+  // (#161), long enough to trip the stall watchdog.
+  const inputSideSeek = isBilibili;
+  if (seekSeconds > 0 && inputSideSeek) args.push("-ss", String(seekSeconds));
   args.push("-i", url);
   // Output-side seek (after -i): works on CDNs that reject Range/keyframe seeks (NetEase music.126.net).
-  if (seekSeconds > 0) args.push("-ss", String(seekSeconds));
+  if (seekSeconds > 0 && !inputSideSeek) args.push("-ss", String(seekSeconds));
   args.push("-f", "s16le", "-ar", "48000", "-ac", "2", "-acodec", "pcm_s16le", "-");
 
   return args;

src/bot/instance.test.ts

@@ -1590,3 +1590,97 @@ describe("BotInstance Bilibili multi-P resolution", () => {
   });
 });
 
+
+describe("resumeInterruptedStream — long B站 streams dying mid-play (#161)", () => {
+  const resumeInterruptedStream = (BotInstance.prototype as any).resumeInterruptedStream as (
+    this: unknown,
+  ) => Promise<boolean>;
+
+  function makeCtx(opts: { platform?: string; elapsed?: number; duration?: number; url?: string | null } = {}) {
+    const song: any = {
+      id: "BV1abc", name: "Long", artist: "A", album: "", coverUrl: "",
+      platform: opts.platform ?? "bilibili", duration: opts.duration ?? 10_000, url: "old",
+    };
+    let elapsed = opts.elapsed ?? 1000;
+    let state: "idle" | "playing" = "idle";
+    const provider = {
+      getSongUrl: vi.fn(async () => (opts.url === null ? null : { url: opts.url ?? "https://fresh.test/a.m4s" })),
+    };
+    const ctx: any = {
+      song,
+      provider,
+      connected: true,
+      effectiveDuration: song.duration,
+      streamRecovery: null,
+      queue: { current: vi.fn(() => song) },
+      player: {
+        getElapsed: vi.fn(() => elapsed),
+        getState: vi.fn(() => state),
+        play: vi.fn(() => { state = "playing"; }),
+      },
+      getProviderFor: vi.fn(() => provider),
+      logger: { warn: vi.fn(), info: vi.fn() },
+      emit: vi.fn(),
+      setElapsed: (v: number) => { elapsed = v; state = "idle"; },
+    };
+    return ctx;
+  }
+
+  it("re-resolves the URL and resumes at the current position when a B站 stream ends early", async () => {
+    const ctx = makeCtx({ elapsed: 1000, duration: 10_000 });
+    expect(await resumeInterruptedStream.call(ctx)).toBe(true);
+    expect(ctx.provider.getSongUrl).toHaveBeenCalledWith("BV1abc");
+    expect(ctx.player.play).toHaveBeenCalledWith("https://fresh.test/a.m4s", 1000, 10_000);
+    expect(ctx.song.url).toBe("https://fresh.test/a.m4s");
+  });
+
+  it("does nothing near the real end of the track (normal EOF)", async () => {
+    const ctx = makeCtx({ elapsed: 9_990, duration: 10_000 });
+    expect(await resumeInterruptedStream.call(ctx)).toBe(false);
+    expect(ctx.provider.getSongUrl).not.toHaveBeenCalled();
+  });
+
+  it("does nothing for other platforms or an unknown duration", async () => {
+    expect(await resumeInterruptedStream.call(makeCtx({ platform: "netease" }))).toBe(false);
+    const unknown = makeCtx({ duration: 0 });
+    unknown.effectiveDuration = 0;
+    expect(await resumeInterruptedStream.call(unknown)).toBe(false);
+  });
+
+  it("gives up after 3 attempts that make no progress, then lets the queue advance", async () => {
+    const ctx = makeCtx({ elapsed: 1000 });
+    for (let i = 0; i < 3; i++) {
+      ctx.setElapsed(1000);
+      expect(await resumeInterruptedStream.call(ctx)).toBe(true);
+    }
+    ctx.setElapsed(1000);
+    expect(await resumeInterruptedStream.call(ctx)).toBe(false);
+    expect(ctx.player.play).toHaveBeenCalledTimes(3);
+  });
+
+  it("resets the attempt budget once a resume actually plays on for a while", async () => {
+    const ctx = makeCtx({ elapsed: 1000 });
+    for (let i = 0; i < 3; i++) {
+      ctx.setElapsed(1000);
+      await resumeInterruptedStream.call(ctx);
+    }
+    ctx.setElapsed(2000); // the last resume played ~16 more minutes
+    expect(await resumeInterruptedStream.call(ctx)).toBe(true);
+  });
+
+  it("falls through to advancing when no fresh URL can be fetched", async () => {
+    const ctx = makeCtx({ url: null });
+    expect(await resumeInterruptedStream.call(ctx)).toBe(false);
+    expect(ctx.player.play).not.toHaveBeenCalled();
+  });
+
+  it("does not clobber a different track the user started while the URL was resolving", async () => {
+    const ctx = makeCtx();
+    ctx.provider.getSongUrl.mockImplementation(async () => {
+      ctx.queue.current.mockReturnValue({ id: "other" }); // user ran !next meanwhile
+      return { url: "https://fresh.test/a.m4s" };
+    });
+    expect(await resumeInterruptedStream.call(ctx)).toBe(true); // handled: don't advance again
+    expect(ctx.player.play).not.toHaveBeenCalled();
+  });
+});

src/bot/instance.ts

@@ -193,6 +193,8 @@ export class BotInstance extends EventEmitter {
   private lastSearchResults: Song[] = [];
   /** 当前曲实际播放时长（试听片段秒数或完整 duration）；resolveAndPlay 赋值。 */
   private effectiveDuration: number | undefined;
+  /** Resume attempts for the current song's stream (#161); see resumeInterruptedStream. */
+  private streamRecovery: { song: QueuedSong; attempts: number; position: number } | null = null;
   private playGate: Promise<unknown> = Promise.resolve();
   /** Per-bot Jellyfin playback-report session (start / ~10s progress / stop).
    *  null when the wired provider has no reporting capability. */
@@ -322,10 +324,19 @@ export class BotInstance extends EventEmitter {
     });
 
     this.player.on("trackEnd", () => {
-      this.logger.debug("Track ended, advancing queue");
-      this.playNext().catch((err) => {
-        this.logger.error({ err }, "playNext failed after trackEnd");
-      });
+      this.resumeInterruptedStream()
+        .catch((err) => {
+          this.logger.warn({ err }, "Stream resume failed");
+          return false;
+        })
+        .then((resumed) => {
+          if (resumed) return;
+          this.logger.debug("Track ended, advancing queue");
+          return this.playNext();
+        })
+        .catch((err) => {
+          this.logger.error({ err }, "playNext failed after trackEnd");
+        });
     });
 
     this.player.on("error", (err: Error) => {
@@ -1116,6 +1127,69 @@ export class BotInstance extends EventEmitter {
     }
   }
 
+  /** Platforms whose CDN stream can die mid-file on long content (#89, #161). */
+  private static readonly RESUMABLE_PLATFORMS: ReadonlySet<Platform> = new Set(["bilibili"]);
+  /** A track that ends within this many seconds of its duration ended normally. */
+  private static readonly STREAM_END_TOLERANCE_S = 30;
+  private static readonly MAX_STREAM_RESUMES = 3;
+
+  /**
+   * Called when the player reports a track end. If a B站 stream ended long
+   * before its known duration, the CDN dropped it (#161): fetch a fresh URL
+   * and continue from where it stopped instead of skipping the rest of a
+   * 2-3 hour video. Gives up after MAX_STREAM_RESUMES attempts that make no
+   * real progress, so a truly broken stream still advances the queue.
+   *
+   * Returns true when it handled the end (resumed, or a newer track has
+   * already taken over), false when the caller should advance the queue.
+   */
+  private async resumeInterruptedStream(): Promise<boolean> {
+    const song = this.queue.current();
+    if (!song || !this.connected || !BotInstance.RESUMABLE_PLATFORMS.has(song.platform)) {
+      return false;
+    }
+    const duration = this.effectiveDuration ?? song.duration;
+    const position = Math.floor(this.player.getElapsed());
+    if (!(duration > 0) || duration - position <= BotInstance.STREAM_END_TOLERANCE_S) {
+      return false;
+    }
+
+    const recovery = this.streamRecovery;
+    if (
+      !recovery ||
+      recovery.song !== song ||
+      position - recovery.position > BotInstance.STREAM_END_TOLERANCE_S
+    ) {
+      this.streamRecovery = { song, attempts: 0, position };
+    }
+    const state = this.streamRecovery!;
+    if (state.attempts >= BotInstance.MAX_STREAM_RESUMES) {
+      this.logger.warn(
+        { songId: song.id, position, duration, attempts: state.attempts },
+        "Stream keeps ending early — giving up and advancing",
+      );
+      this.streamRecovery = null;
+      return false;
+    }
+    state.attempts++;
+    state.position = position;
+
+    this.logger.warn(
+      { songId: song.id, position, duration, attempt: state.attempts },
+      "Stream ended before the track did — resuming with a fresh URL",
+    );
+    const result = await this.getProviderFor(song.platform).getSongUrl(song.id);
+    // The user may have skipped/stopped while we were resolving; never
+    // clobber whatever is playing now.
+    if (this.queue.current() !== song || this.player.getState() !== "idle") return true;
+    if (!result?.url || !this.connected) return false;
+
+    song.url = result.url;
+    this.player.play(result.url, position, duration);
+    this.emit("stateChange");
+    return true;
+  }
+
   private async syncProfileToSong(song: QueuedSong | null): Promise<void> {
     try {
       await this.profileManager.onSongChange(song);

src/music/bilibili.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi } from "vitest";
-import { BiliBiliProvider } from "./bilibili.js";
+import { BiliBiliProvider, pickStableAudioUrl } from "./bilibili.js";
 
 describe("BiliBiliProvider.search pagination", () => {
   function mockProvider() {
@@ -162,3 +162,44 @@ describe("BiliBiliProvider multi-P support", () => {
     expect(playurlCall![1].params.bvid).toBe("BV1multiP"); // 纯净 bvid
   });
 });
+
+describe("pickStableAudioUrl (#161 long streams dying mid-play)", () => {
+  const pcdn = "https://xy1x2x3x4xy.mcdn.bilivideo.cn:4483/upgcxcode/1/2/3/3-1-30280.m4s?e=x&deadline=1";
+  const szbdyd = "https://cn-hk-eq-01-01.szbdyd.com/upgcxcode/1/2/3/3-1-30280.m4s?deadline=1";
+  const upos = "https://upos-sz-mirrorcos.bilivideo.com/upgcxcode/1/2/3/3-1-30280.m4s?deadline=1";
+  const upos2 = "https://upos-sz-mirror08c.bilivideo.com/upgcxcode/1/2/3/3-1-30280.m4s?deadline=1";
+
+  it("prefers an upos/cos mirror over a PCDN baseUrl", () => {
+    expect(pickStableAudioUrl({ baseUrl: pcdn, backupUrl: [szbdyd, upos] })).toBe(upos);
+  });
+
+  it("keeps the baseUrl when it is already a stable host", () => {
+    expect(pickStableAudioUrl({ baseUrl: upos, backupUrl: [upos2] })).toBe(upos);
+  });
+
+  it("accepts the snake_case field names", () => {
+    expect(pickStableAudioUrl({ base_url: pcdn, backup_url: [upos2] })).toBe(upos2);
+  });
+
+  it("falls back to the baseUrl when every candidate is PCDN", () => {
+    expect(pickStableAudioUrl({ baseUrl: pcdn, backupUrl: [szbdyd] })).toBe(pcdn);
+  });
+
+  it("returns undefined when there is no url at all", () => {
+    expect(pickStableAudioUrl({})).toBeUndefined();
+  });
+
+  it("getSongUrl returns the stable mirror of the best stream", async () => {
+    const p = new BiliBiliProvider();
+    (p as any).cidCache.set("BV1abc", 42);
+    (p as any).api = {
+      get: vi.fn().mockResolvedValue({
+        data: { data: { dash: { audio: [
+          { bandwidth: 64000, baseUrl: "https://upos-sz-mirrorcos.bilivideo.com/low.m4s" },
+          { bandwidth: 320000, baseUrl: pcdn, backupUrl: [upos] },
+        ] } } },
+      }),
+    };
+    expect((await p.getSongUrl("BV1abc"))?.url).toBe(upos);
+  });
+});

src/music/bilibili.ts

@@ -42,6 +42,37 @@ export interface BiliVideoPartsResult {
   parts: BiliVideoPart[];
 }
 
+/**
+ * PCDN / P2P edge hosts (xy*.mcdn.bilivideo.cn:<port>, *.szbdyd.com). Their
+ * sessions get cut mid-file, which kills long streams partway (#89, #161),
+ * and a reconnect to the same host rarely recovers.
+ */
+const BILI_PCDN_HOST = /\.mcdn\.bilivideo\.cn$|\.szbdyd\.com$/i;
+
+/**
+ * Pick the audio URL least likely to die mid-stream: the first upos/cos
+ * mirror among baseUrl + backupUrl, else the baseUrl as before.
+ */
+export function pickStableAudioUrl(stream: {
+  baseUrl?: string;
+  base_url?: string;
+  backupUrl?: string[];
+  backup_url?: string[];
+}): string | undefined {
+  const primary = stream.baseUrl ?? stream.base_url;
+  const candidates = [primary, ...(stream.backupUrl ?? stream.backup_url ?? [])].filter(
+    (u): u is string => typeof u === "string" && u.length > 0,
+  );
+  const stable = candidates.find((u) => {
+    try {
+      return !BILI_PCDN_HOST.test(new URL(u).hostname);
+    } catch {
+      return false;
+    }
+  });
+  return stable ?? primary;
+}
+
 /**
  * 解析带有分P信息的 B站 ID 或 URL。
  * 支持形如 "BVxxxx", "BVxxxx?p=2", "BVxxxx:p2" 以及完整 URL 等格式，默认 page 为 1。
@@ -353,7 +384,7 @@ export class BiliBiliProvider implements MusicProvider {
         (b.bandwidth ?? 0) > (a.bandwidth ?? 0) ? b : a
       );
 
-      const biliUrl = best.baseUrl ?? best.base_url;
+      const biliUrl = pickStableAudioUrl(best);
       return biliUrl ? { url: biliUrl } : null;
     } catch {
       return null;