ChatApp/apps/desktop/electron/modules/screen-audio.ts

// System-audio loopback — renderer-driven. Chromium's
// `chromeMediaSource: 'desktop'` constraint on getUserMedia accepts a
// source id and returns a MediaStream that contains the OS mixer output.
// Main's only job is to resolve which source id the renderer should feed
// to getUserMedia (typically the primary screen). See the display-media
// handler in main.ts which grants the request automatically.

import { desktopCapturer, ipcMain } from 'electron';

import { CHANNELS } from '../ipc-types';

export interface ResolveLoopbackSourceResult {
  sourceId: string;
}

export function register(): void {
  ipcMain.handle(
    CHANNELS.AUDIO_LOOPBACK_RESOLVE_SOURCE,
    async (): Promise<ResolveLoopbackSourceResult | null> => {
      // Enumerate only screens; windows don't expose audio loopback on
      // Windows and there's no meaningful "system audio" tied to a
      // single window anyway. Primary screen is the first entry — the
      // id is stable across calls as long as the display config doesn't
      // change mid-session.
      const sources = await desktopCapturer.getSources({
        types: ['screen'],
        fetchWindowIcons: false,
      });
      const first = sources[0];
      if (!first) return null;
      return { sourceId: first.id };
    },
  );

  // The legacy start/stop channels are left unregistered on purpose —
  // their constants still exist in ipc-types.ts for backwards compatible
  // import paths, but there is no corresponding handler.
}