feat: add opt-in save-before-playing setting backed by server-compiled single-file downloads

server/server.js

@@ -24,7 +24,9 @@ import { serveStatic }  from 'hono/bun';
 import { logger }       from 'hono/logger';
 import { spawn }        from 'node:child_process';
 import { createServer } from 'node:http';
-import { readFileSync, readdirSync, statSync } from 'node:fs';
+import { readFileSync, readdirSync, statSync, openSync, unlinkSync, createReadStream } from 'node:fs';
+import { Readable }      from 'node:stream';
+import { tmpdir }        from 'node:os';
 import { createHash }    from 'node:crypto';
 import { initDb, upsertUser, recordVideoAccess, getUserData } from './db.js';
 
@@ -305,6 +307,53 @@ app.get('/api/download/:videoId', async (c) => {
 
   try {
     const url = `https://www.youtube.com/watch?v=${videoId}`;
+
+    // ?mux=1 — "Save before playing" path: let yt-dlp download bestvideo up
+    // to 720p PLUS bestaudio and compile them into one mp4 with ffmpeg on
+    // the server, then stream the finished file. Default saves (no mux)
+    // keep the progressive single-stream behavior below, unchanged.
+    if (c.req.query('mux') === '1') {
+      const tmp = `${tmpdir()}/ytp-mux-${videoId}-${Date.now()}.mp4`;
+      try {
+        await runYtdlp([
+          url,
+          '--no-warnings', '--no-playlist',
+          '-f', 'bv*[height<=720][ext=mp4]+ba[ext=m4a]/bv*[height<=720]+ba/b[ext=mp4]/b',
+          '--merge-output-format', 'mp4',
+          '-N', '4',
+          '-o', tmp,
+        ]);
+        const size = statSync(tmp).size;
+        // Open the fd first, then unlink: on Linux the data stays readable
+        // until the fd closes, so the temp file cleans itself up even if the
+        // client disconnects mid-transfer.
+        const fd = openSync(tmp, 'r');
+        unlinkSync(tmp);
+        const stream = createReadStream('', { fd });
+
+        const fp = c.req.query('fp');
+        if (fp) recordVideoAccess(fp, { id: videoId }).catch(() => {});
+
+        return new Response(Readable.toWeb(stream), {
+          status: 200,
+          headers: {
+            'Content-Type':        'video/mp4',
+            'Content-Length':      String(size),
+            'Content-Disposition': `attachment; filename="${videoId}.mp4"`,
+            'Cache-Control':       'no-store',
+            'Access-Control-Allow-Origin': '*',
+          },
+        });
+      } catch (err) {
+        // ffmpeg missing or extraction failed — clean up any partial output
+        // and fall through to the progressive proxy below.
+        for (const leftover of [tmp, tmp + '.part']) {
+          try { unlinkSync(leftover); } catch { /* not created */ }
+        }
+        console.warn(`[ytplayer] mux download failed for ${videoId}, falling back to progressive:`, err.message);
+      }
+    }
+
     // --get-url with bestvideo+bestaudio/best format is not what we want
     // here — we need a SINGLE FILE so no ffmpeg muxing is required in the
     // browser. Use -f "bestvideo[ext=mp4][acodec!=none]/best[ext=mp4]/best"