feat(mining): cache remote media windows during card creation

- Reuse one temporary download for timing review, audio, and screenshots
- Expire cached windows after inactivity and clean them up on exit

src/core/services/media-timing-preview.test.ts

@@ -23,6 +23,21 @@ describe('buildMediaTimingPreviewArgs', () => {
     assert.equal(args.at(-1), '/video/show.mkv');
   });
 
+  test('keeps source timestamps for cached remote windows', () => {
+    const args = buildMediaTimingPreviewArgs('/tmp/review.sock', {
+      mediaPath: '/tmp/window.mkv',
+      absoluteTimestamps: true,
+    });
+
+    assert.ok(args.includes('--rebase-start-time=no'));
+    assert.equal(
+      buildMediaTimingPreviewArgs('/tmp/review.sock', { mediaPath: '/video/show.mkv' }).includes(
+        '--rebase-start-time=no',
+      ),
+      false,
+    );
+  });
+
   test('separates an option-like media path without adding optional audio arguments', () => {
     const args = buildMediaTimingPreviewArgs('/tmp/review.sock', {
       mediaPath: '--fullscreen',

src/core/services/media-timing-preview.ts

@@ -14,6 +14,8 @@ export interface MediaTimingPreviewStartOptions {
   executablePath?: string;
   audioTrackId?: number;
   volume?: number;
+  /** The file keeps source timestamps (a cached remote window); seek with the original times. */
+  absoluteTimestamps?: boolean;
 }
 
 type PreviewProcess = Pick<ChildProcess, 'kill' | 'once'>;
@@ -51,6 +53,9 @@ export function buildMediaTimingPreviewArgs(
   if (typeof options.volume === 'number' && Number.isFinite(options.volume)) {
     args.push(`--volume=${Math.max(0, options.volume)}`);
   }
+  if (options.absoluteTimestamps) {
+    args.push('--rebase-start-time=no');
+  }
   args.push('--', options.mediaPath);
   return args;
 }

src/core/services/media-timing-waveform.test.ts

@@ -35,6 +35,29 @@ test('speech waveform maps the selected FFmpeg stream and visible range', () =>
   assert.match(args[args.indexOf('-af') + 1] ?? '', /c0=FC/);
 });
 
+test('speech waveform seeks cached windows by source timestamps', () => {
+  const args = buildSpeechWaveformArgs(
+    {
+      mediaPath: { path: '/tmp/window.mkv', absoluteTimestamps: true, singleResolvedStream: true },
+      startTime: 8,
+      endTime: 15,
+    },
+    'downmix',
+  );
+
+  assert.deepEqual(args.slice(args.indexOf('-ss'), args.indexOf('-t') + 2), [
+    '-ss',
+    '8',
+    '-seek_timestamp',
+    '1',
+    '-i',
+    '/tmp/window.mkv',
+    '-t',
+    '7',
+  ]);
+  assert.equal(args.includes('-map'), false);
+});
+
 test('waveform peaks are normalized without flattening quieter sections', () => {
   const peaks = computeWaveformPeaks(pcm([0, 1_000, -2_000, 4_000, -8_000, 16_000]), 3);
 

src/core/services/media-timing-waveform.ts

@@ -1,4 +1,5 @@
 import { spawn } from 'node:child_process';
+import { normalizeMediaInput, type MediaInput } from '../../media-input';
 
 const WAVEFORM_SAMPLE_RATE = 8_000;
 const WAVEFORM_POINT_COUNT = 480;
@@ -9,7 +10,7 @@ const CENTER_CHANNEL_FILTER = `pan=mono|c0=FC,${SPEECH_FILTER}`;
 const DOWNMIX_FILTER = `aformat=channel_layouts=mono,${SPEECH_FILTER}`;
 
 export interface SpeechWaveformOptions {
-  mediaPath: string;
+  mediaPath: MediaInput;
   startTime: number;
   endTime: number;
   audioStreamIndex?: number;
@@ -22,6 +23,7 @@ export function buildSpeechWaveformArgs(
   mode: 'center' | 'downmix',
 ): string[] {
   const duration = options.endTime - options.startTime;
+  const input = normalizeMediaInput(options.mediaPath);
   const args = [
     '-hide_banner',
     '-nostdin',
@@ -29,8 +31,9 @@ export function buildSpeechWaveformArgs(
     'error',
     '-ss',
     String(options.startTime),
+    ...input.inputArgs,
     '-i',
-    options.mediaPath,
+    input.path,
     '-t',
     String(duration),
   ];

src/core/services/remote-media-window-cache.test.ts

@@ -0,0 +1,253 @@
+import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import test from 'node:test';
+import {
+  buildRemoteMediaWindowArgs,
+  RemoteMediaWindowCache,
+  REMOTE_MEDIA_WINDOW_MAX_SECONDS,
+  type RemoteMediaWindowCacheOptions,
+} from './remote-media-window-cache';
+
+const SOURCE = {
+  path: 'https://jellyfin.example/Videos/abc/stream?static=true',
+  audioStreamIndex: 2,
+};
+
+type ExecFileStub = NonNullable<RemoteMediaWindowCacheOptions['execFile']>;
+
+function createStub(options: { fail?: boolean; empty?: boolean; defer?: boolean } = {}) {
+  const calls: string[][] = [];
+  const pendingCallbacks: Array<() => void> = [];
+  const execFile: ExecFileStub = (_file, args, _options, callback) => {
+    calls.push([...args]);
+    const finish = (): void => {
+      const outputPath = args.at(-1);
+      assert.ok(outputPath);
+      if (options.fail) {
+        callback(Object.assign(new Error('boom'), { code: 1 }));
+        return;
+      }
+      if (!options.empty) {
+        fs.writeFileSync(outputPath, 'mkv', 'utf8');
+      }
+      callback(null);
+    };
+    if (options.defer) {
+      pendingCallbacks.push(finish);
+    } else {
+      queueMicrotask(finish);
+    }
+  };
+  return {
+    calls,
+    execFile,
+    flush: () => {
+      for (const finish of pendingCallbacks.splice(0)) finish();
+    },
+  };
+}
+
+async function withCache(
+  stubOptions: Parameters<typeof createStub>[0],
+  cacheOptions: Omit<RemoteMediaWindowCacheOptions, 'execFile' | 'tempDir'>,
+  run: (cache: RemoteMediaWindowCache, stub: ReturnType<typeof createStub>) => Promise<void>,
+): Promise<void> {
+  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'subminer-media-window-test-'));
+  const stub = createStub(stubOptions);
+  const cache = new RemoteMediaWindowCache({
+    tempDir,
+    execFile: stub.execFile,
+    idleTtlMs: 0,
+    logDebug: () => undefined,
+    ...cacheOptions,
+  });
+  try {
+    await run(cache, stub);
+  } finally {
+    cache.cleanup();
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  }
+}
+
+function argValue(args: string[], flag: string): string | undefined {
+  const index = args.indexOf(flag);
+  return index === -1 ? undefined : args[index + 1];
+}
+
+test('buildRemoteMediaWindowArgs stream-copies the window with source timestamps intact', () => {
+  const args = buildRemoteMediaWindowArgs(
+    { ...SOURCE, inputOptions: { reconnect: true, headers: { Referer: 'https://a.example/' } } },
+    { startTime: 22.75, endTime: 33 },
+    '/tmp/window.mkv',
+  );
+
+  const inputIndex = args.indexOf('-i');
+  assert.equal(args[inputIndex + 1], SOURCE.path);
+  assert.ok(args.indexOf('-reconnect') < inputIndex);
+  assert.ok(args.indexOf('-headers') < inputIndex);
+  assert.equal(argValue(args, '-ss'), '22.75');
+  assert.equal(argValue(args, '-t'), '10.25');
+  assert.ok(args.indexOf('-t') < inputIndex);
+  assert.deepEqual(args.slice(args.indexOf('-map'), args.indexOf('-map') + 4), [
+    '-map',
+    '0:v:0?',
+    '-map',
+    '0:2',
+  ]);
+  assert.equal(argValue(args, '-c'), 'copy');
+  assert.ok(args.includes('-copyts'));
+  assert.ok(args.includes('-start_at_zero'));
+  assert.equal(argValue(args, '-f'), 'matroska');
+  assert.equal(args.at(-1), '/tmp/window.mkv');
+});
+
+test('buildRemoteMediaWindowArgs keeps every audio stream when none is selected', () => {
+  const args = buildRemoteMediaWindowArgs(
+    { path: SOURCE.path, audioStreamIndex: null },
+    { startTime: 0, endTime: 5 },
+    '/tmp/window.mkv',
+  );
+
+  assert.equal(args[args.lastIndexOf('-map') + 1], '0:a');
+});
+
+test('acquire downloads once and reuses the window for covered ranges', async () => {
+  await withCache({}, {}, async (cache, stub) => {
+    const window = await cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+
+    assert.equal(stub.calls.length, 1);
+    assert.equal(argValue(stub.calls[0]!, '-ss'), '9.75');
+    assert.equal(argValue(stub.calls[0]!, '-t'), '5.25');
+    assert.equal(window.startTime, 9.75);
+    assert.equal(window.endTime, 15);
+    assert.equal(window.audioStreamIndex, 2);
+    assert.ok(fs.existsSync(window.path));
+    assert.deepEqual(window.media, {
+      path: window.path,
+      source: 'remote-window',
+      singleResolvedStream: true,
+      absoluteTimestamps: true,
+    });
+
+    assert.equal(await cache.acquire(SOURCE, { startTime: 11, endTime: 15 }), window);
+    assert.equal(await cache.lookup(SOURCE, { startTime: 12, endTime: 12 }), window);
+    assert.equal(
+      await cache.lookup(
+        { path: SOURCE.path, audioStreamIndex: null },
+        { startTime: 12, endTime: 13 },
+      ),
+      window,
+    );
+    assert.equal(stub.calls.length, 1);
+  });
+});
+
+test('lookup never downloads and misses on other ranges, sources, or audio streams', async () => {
+  await withCache({}, {}, async (cache, stub) => {
+    assert.equal(await cache.lookup(SOURCE, { startTime: 10, endTime: 14 }), null);
+    assert.equal(stub.calls.length, 0);
+
+    await cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+    assert.equal(await cache.lookup(SOURCE, { startTime: 14, endTime: 16 }), null);
+    assert.equal(
+      await cache.lookup(
+        { path: 'https://other.example/stream', audioStreamIndex: 2 },
+        {
+          startTime: 11,
+          endTime: 12,
+        },
+      ),
+      null,
+    );
+    assert.equal(
+      await cache.lookup(
+        { path: SOURCE.path, audioStreamIndex: 3 },
+        { startTime: 11, endTime: 12 },
+      ),
+      null,
+    );
+    assert.equal(stub.calls.length, 1);
+  });
+});
+
+test('acquire widens to the union of the old window and replaces the old file', async () => {
+  await withCache({}, {}, async (cache, stub) => {
+    const first = await cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+    const second = await cache.acquire(SOURCE, { startTime: 8, endTime: 12 });
+
+    assert.equal(stub.calls.length, 2);
+    assert.equal(argValue(stub.calls[1]!, '-ss'), '7.75');
+    assert.equal(second.startTime, 7.75);
+    assert.equal(second.endTime, 15);
+    assert.notEqual(second.path, first.path);
+    assert.equal(fs.existsSync(first.path), false);
+    assert.ok(fs.existsSync(second.path));
+    assert.equal(cache.currentWindow, second);
+  });
+});
+
+test('acquire shares an in-flight download between concurrent callers', async () => {
+  await withCache({ defer: true }, {}, async (cache, stub) => {
+    const first = cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+    await Promise.resolve();
+    const second = cache.acquire(SOURCE, { startTime: 11, endTime: 13 });
+    const lookup = cache.lookup(SOURCE, { startTime: 12, endTime: 12 });
+    await Promise.resolve();
+    assert.equal(stub.calls.length, 1);
+
+    stub.flush();
+    const [a, b, c] = await Promise.all([first, second, lookup]);
+    assert.equal(a, b);
+    assert.equal(a, c);
+    assert.equal(stub.calls.length, 1);
+  });
+});
+
+test('acquire rejects on ffmpeg failure, leaves no file, and can retry', async () => {
+  await withCache({ fail: true }, {}, async (cache, stub) => {
+    await assert.rejects(
+      cache.acquire(SOURCE, { startTime: 10, endTime: 14 }),
+      /FFmpeg media window failed: boom/,
+    );
+    assert.equal(cache.currentWindow, null);
+    assert.equal(await cache.lookup(SOURCE, { startTime: 10, endTime: 14 }), null);
+
+    await assert.rejects(cache.acquire(SOURCE, { startTime: 10, endTime: 14 }));
+    assert.equal(stub.calls.length, 2);
+  });
+  await withCache({ empty: true }, {}, async (cache) => {
+    await assert.rejects(
+      cache.acquire(SOURCE, { startTime: 10, endTime: 14 }),
+      /exited without creating a media window/,
+    );
+  });
+});
+
+test('acquire refuses invalid and oversized ranges without spawning ffmpeg', async () => {
+  await withCache({}, {}, async (cache, stub) => {
+    await assert.rejects(cache.acquire(SOURCE, { startTime: 10, endTime: 10 }), /invalid/);
+    await assert.rejects(cache.acquire(SOURCE, { startTime: -1, endTime: 10 }), /invalid/);
+    await assert.rejects(
+      cache.acquire(SOURCE, { startTime: 0, endTime: REMOTE_MEDIA_WINDOW_MAX_SECONDS + 1 }),
+      /too long/,
+    );
+    assert.equal(stub.calls.length, 0);
+  });
+});
+
+test('the window is deleted after the idle timeout and on cleanup', async () => {
+  await withCache({}, { idleTtlMs: 20 }, async (cache) => {
+    const window = await cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+    await new Promise((resolve) => setTimeout(resolve, 60));
+
+    assert.equal(cache.currentWindow, null);
+    assert.equal(fs.existsSync(window.path), false);
+
+    const again = await cache.acquire(SOURCE, { startTime: 10, endTime: 14 });
+    cache.cleanup();
+    assert.equal(fs.existsSync(again.path), false);
+    assert.equal(fs.existsSync(path.dirname(again.path)), false);
+  });
+});

src/core/services/remote-media-window-cache.ts

@@ -0,0 +1,377 @@
+import { execFile as nodeExecFile, type ExecFileException } from 'child_process';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { createLogger } from '../../logger';
+import { normalizeMediaInput, type MediaInput, type MediaInputOptions } from '../../media-input';
+
+const log = createLogger('media-window');
+
+export const REMOTE_MEDIA_WINDOW_TIMEOUT_MS = 120_000;
+export const REMOTE_MEDIA_WINDOW_MAX_SECONDS = 180;
+const HEAD_SLACK_SECONDS = 0.25;
+const TAIL_SLACK_SECONDS = 1;
+const DEFAULT_IDLE_TTL_MS = 10 * 60_000;
+const COVERAGE_EPSILON_SECONDS = 0.01;
+
+export interface RemoteMediaWindowSource {
+  path: string;
+  inputOptions?: MediaInputOptions;
+  /** FFmpeg stream index to keep; `null`/undefined keeps every audio stream. */
+  audioStreamIndex?: number | null;
+}
+
+export interface RemoteMediaWindowRange {
+  startTime: number;
+  endTime: number;
+}
+
+export interface RemoteMediaWindow {
+  path: string;
+  startTime: number;
+  endTime: number;
+  sourcePath: string;
+  audioStreamIndex: number | null;
+  /** Input descriptor for FFmpeg reads; timestamps stay absolute so callers keep source times. */
+  media: MediaInput;
+}
+
+type WindowExecFile = (
+  file: string,
+  args: readonly string[],
+  options: { timeout: number },
+  callback: (error: ExecFileException | null) => void,
+) => void;
+
+export interface RemoteMediaWindowCacheOptions {
+  tempDir?: string;
+  execFile?: WindowExecFile;
+  idleTtlMs?: number;
+  logDebug?: (message: string) => void;
+}
+
+interface PendingFetch extends RemoteMediaWindowRange {
+  sourcePath: string;
+  audioStreamIndex: number | null;
+  promise: Promise<RemoteMediaWindow>;
+}
+
+export function isRemoteMediaWindowSourcePath(value: string): boolean {
+  return /^https?:\/\//i.test(value.trim());
+}
+
+function describeSourceForDebugLog(sourcePath: string): string {
+  try {
+    return `remote:${new URL(sourcePath).hostname.toLowerCase() || 'unknown'}`;
+  } catch {
+    return 'remote:unknown';
+  }
+}
+
+function isUsableRange(range: RemoteMediaWindowRange, allowEmpty: boolean): boolean {
+  return (
+    Number.isFinite(range.startTime) &&
+    Number.isFinite(range.endTime) &&
+    range.startTime >= 0 &&
+    (allowEmpty ? range.endTime >= range.startTime : range.endTime > range.startTime)
+  );
+}
+
+function audioStreamMatches(
+  windowIndex: number | null,
+  requested: number | null | undefined,
+): boolean {
+  return requested == null || windowIndex === requested;
+}
+
+function covers(
+  candidate: RemoteMediaWindowRange & { sourcePath: string; audioStreamIndex: number | null },
+  source: RemoteMediaWindowSource,
+  range: RemoteMediaWindowRange,
+): boolean {
+  return (
+    candidate.sourcePath === source.path &&
+    audioStreamMatches(candidate.audioStreamIndex, source.audioStreamIndex) &&
+    candidate.startTime <= range.startTime + COVERAGE_EPSILON_SECONDS &&
+    candidate.endTime >= range.endTime - COVERAGE_EPSILON_SECONDS
+  );
+}
+
+/**
+ * Stream-copies `[startTime, endTime]` of a remote source into a local Matroska file.
+ * `-copyts -start_at_zero` keeps the source timestamps, so later reads seek with the
+ * original times via `-seek_timestamp 1` (see `MediaInput.absoluteTimestamps`).
+ */
+export function buildRemoteMediaWindowArgs(
+  source: RemoteMediaWindowSource,
+  range: RemoteMediaWindowRange,
+  outputPath: string,
+): string[] {
+  const input = normalizeMediaInput({ path: source.path, inputOptions: source.inputOptions });
+  const audioMap =
+    typeof source.audioStreamIndex === 'number' && Number.isInteger(source.audioStreamIndex)
+      ? `0:${source.audioStreamIndex}`
+      : '0:a';
+  return [
+    '-hide_banner',
+    '-nostdin',
+    '-loglevel',
+    'error',
+    '-ss',
+    String(range.startTime),
+    '-t',
+    String(range.endTime - range.startTime),
+    ...input.inputArgs,
+    '-i',
+    input.path,
+    '-map',
+    '0:v:0?',
+    '-map',
+    audioMap,
+    '-c',
+    'copy',
+    '-sn',
+    '-dn',
+    '-copyts',
+    '-start_at_zero',
+    '-f',
+    'matroska',
+    '-y',
+    outputPath,
+  ];
+}
+
+/**
+ * Holds one downloaded window of the current remote stream so the timing review,
+ * audio extraction, and screenshot all read the same local bytes instead of each
+ * re-fetching the clip over HTTP. A new window replaces the old one; the file is
+ * deleted after `idleTtlMs` without use, on `clear()`, or on `cleanup()`.
+ */
+export class RemoteMediaWindowCache {
+  private readonly tempDir: string;
+  private readonly execFile: WindowExecFile;
+  private readonly idleTtlMs: number;
+  private readonly logDebug: (message: string) => void;
+  private current: RemoteMediaWindow | null = null;
+  private pending: PendingFetch | null = null;
+  private idleTimer: ReturnType<typeof setTimeout> | null = null;
+  private sequence = 0;
+
+  constructor(options: RemoteMediaWindowCacheOptions = {}) {
+    this.tempDir = options.tempDir ?? path.join(os.tmpdir(), 'subminer-media-windows');
+    this.execFile = options.execFile ?? nodeExecFile;
+    this.idleTtlMs = options.idleTtlMs ?? DEFAULT_IDLE_TTL_MS;
+    this.logDebug = options.logDebug ?? ((message) => log.debug(message));
+  }
+
+  get currentWindow(): RemoteMediaWindow | null {
+    return this.current;
+  }
+
+  /** Returns a ready or in-flight window covering the range; never starts a download. */
+  async lookup(
+    source: RemoteMediaWindowSource,
+    range: RemoteMediaWindowRange,
+  ): Promise<RemoteMediaWindow | null> {
+    if (!isUsableRange(range, true)) return null;
+    if (this.current && covers(this.current, source, range)) {
+      this.touch();
+      return this.current;
+    }
+    const pending = this.pending;
+    if (pending && covers(pending, source, range)) {
+      try {
+        const window = await pending.promise;
+        this.touch();
+        return window;
+      } catch {
+        return null;
+      }
+    }
+    return null;
+  }
+
+  /** Returns a window covering the range, downloading (and widening) one when needed. */
+  async acquire(
+    source: RemoteMediaWindowSource,
+    range: RemoteMediaWindowRange,
+  ): Promise<RemoteMediaWindow> {
+    if (!isUsableRange(range, false)) {
+      throw new Error('Media window range is invalid.');
+    }
+    if (range.endTime - range.startTime > REMOTE_MEDIA_WINDOW_MAX_SECONDS) {
+      throw new Error('Media window range is too long to download.');
+    }
+
+    for (;;) {
+      const hit = await this.lookup(source, range);
+      if (hit) return hit;
+      const pending = this.pending;
+      if (!pending) break;
+      // Another caller is already downloading; wait for it, then re-check coverage.
+      await pending.promise.catch(() => null);
+    }
+
+    return this.fetch(source, this.planFetchRange(source, range));
+  }
+
+  clear(): void {
+    this.cancelIdleTimer();
+    const current = this.current;
+    this.current = null;
+    if (current) this.removeFile(current.path);
+  }
+
+  cleanup(): void {
+    this.clear();
+    try {
+      fs.rmSync(this.tempDir, { recursive: true, force: true });
+    } catch (error) {
+      log.error('Failed to cleanup media window directory:', error);
+    }
+  }
+
+  private planFetchRange(
+    source: RemoteMediaWindowSource,
+    range: RemoteMediaWindowRange,
+  ): RemoteMediaWindowRange {
+    let startTime = Math.max(0, range.startTime - HEAD_SLACK_SECONDS);
+    let endTime = range.endTime + TAIL_SLACK_SECONDS;
+    const current = this.current;
+    if (
+      current &&
+      current.sourcePath === source.path &&
+      audioStreamMatches(current.audioStreamIndex, source.audioStreamIndex)
+    ) {
+      // Keep what was already downloaded when the review timeline grows in one direction.
+      const unionStart = Math.min(startTime, current.startTime);
+      const unionEnd = Math.max(endTime, current.endTime);
+      if (unionEnd - unionStart <= REMOTE_MEDIA_WINDOW_MAX_SECONDS) {
+        startTime = unionStart;
+        endTime = unionEnd;
+      }
+    }
+    return { startTime, endTime };
+  }
+
+  private fetch(
+    source: RemoteMediaWindowSource,
+    range: RemoteMediaWindowRange,
+  ): Promise<RemoteMediaWindow> {
+    fs.mkdirSync(this.tempDir, { recursive: true });
+    this.sequence += 1;
+    const outputPath = path.join(this.tempDir, `window_${Date.now()}_${this.sequence}.mkv`);
+    const audioStreamIndex =
+      typeof source.audioStreamIndex === 'number' ? source.audioStreamIndex : null;
+    const description = describeSourceForDebugLog(source.path);
+    const startedAt = Date.now();
+    this.logDebug(
+      `[media-window] fetch start ${description} start=${range.startTime} end=${range.endTime} audioStream=${audioStreamIndex ?? 'all'}`,
+    );
+
+    const promise = new Promise<RemoteMediaWindow>((resolve, reject) => {
+      this.execFile(
+        'ffmpeg',
+        buildRemoteMediaWindowArgs(source, range, outputPath),
+        { timeout: REMOTE_MEDIA_WINDOW_TIMEOUT_MS },
+        (error) => {
+          const elapsedMs = Math.max(0, Date.now() - startedAt);
+          const size = error ? 0 : this.fileSize(outputPath);
+          if (error || size === 0) {
+            this.removeFile(outputPath);
+            const reason = error
+              ? error.code === 'ENOENT'
+                ? 'FFmpeg not found. Install FFmpeg to enable media generation.'
+                : `FFmpeg media window failed: ${error.message}`
+              : 'FFmpeg exited without creating a media window.';
+            this.logDebug(`[media-window] fetch failed ${description} elapsedMs=${elapsedMs}`);
+            reject(new Error(reason));
+            return;
+          }
+          const window: RemoteMediaWindow = {
+            path: outputPath,
+            startTime: range.startTime,
+            endTime: range.endTime,
+            sourcePath: source.path,
+            audioStreamIndex,
+            media: {
+              path: outputPath,
+              source: 'remote-window',
+              singleResolvedStream: true,
+              absoluteTimestamps: true,
+            },
+          };
+          this.logDebug(
+            `[media-window] fetch complete ${description} elapsedMs=${elapsedMs} bytes=${size}`,
+          );
+          this.replaceCurrent(window);
+          resolve(window);
+        },
+      );
+    });
+
+    const pending: PendingFetch = {
+      sourcePath: source.path,
+      audioStreamIndex,
+      startTime: range.startTime,
+      endTime: range.endTime,
+      promise,
+    };
+    this.pending = pending;
+    promise
+      .catch(() => undefined)
+      .then(() => {
+        if (this.pending === pending) this.pending = null;
+      });
+    return promise;
+  }
+
+  private replaceCurrent(window: RemoteMediaWindow): void {
+    const previous = this.current;
+    this.current = window;
+    if (previous && previous.path !== window.path) this.removeFile(previous.path);
+    this.touch();
+  }
+
+  private touch(): void {
+    this.cancelIdleTimer();
+    if (this.idleTtlMs <= 0 || !this.current) return;
+    const timer = setTimeout(() => {
+      if (this.idleTimer === timer) this.idleTimer = null;
+      this.clear();
+    }, this.idleTtlMs);
+    timer.unref?.();
+    this.idleTimer = timer;
+  }
+
+  private cancelIdleTimer(): void {
+    if (this.idleTimer) clearTimeout(this.idleTimer);
+    this.idleTimer = null;
+  }
+
+  private fileSize(filePath: string): number {
+    try {
+      return fs.statSync(filePath).size;
+    } catch {
+      return 0;
+    }
+  }
+
+  private removeFile(filePath: string): void {
+    try {
+      fs.unlinkSync(filePath);
+    } catch (error) {
+      if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
+        log.debug(`Failed to remove media window ${filePath}:`, (error as Error).message);
+      }
+    }
+  }
+}
+
+let sharedCache: RemoteMediaWindowCache | null = null;
+
+/** Process-wide cache so the review modal and card media generation share one download. */
+export function getSharedRemoteMediaWindowCache(): RemoteMediaWindowCache {
+  sharedCache ??= new RemoteMediaWindowCache();
+  return sharedCache;
+}