diff --git a/src/servers/api/tasks/task-executor.ts b/src/servers/api/tasks/task-executor.ts
index ed951787..e6544e11 100644
--- a/src/servers/api/tasks/task-executor.ts
+++ b/src/servers/api/tasks/task-executor.ts
@@ -235,6 +235,13 @@ async function handleRun(ws: ServerWebSocket<WSData>, msg: RunMessage) {
       },
     });
 
+    // Keep the WebSocket alive during long silent phases (e.g. ffmpeg's faststart pass rewrites a huge
+    // file for minutes with no output). Bun's default 120s idle timeout would otherwise close the
+    // socket → close(ws) → killTree kills the task mid-run. A ping resets the idle timer.
+    const keepAlive = setInterval(() => {
+      try { ws.ping(); } catch { /* socket gone */ }
+    }, 30_000);
+
     const stdoutReader = proc.stdout.getReader();
     const stderrReader = proc.stderr.getReader();
     const decoder = new TextDecoder();
@@ -257,6 +264,7 @@ async function handleRun(ws: ServerWebSocket<WSData>, msg: RunMessage) {
       proc.exited,
     ]);
 
+    clearInterval(keepAlive);
     activeProcs.delete(ws);
     cleanup();
     send(ws, { type: 'exit', code: exitCode });