Speed up transcoding without overloading the VM, add bulk retry

- nice level 19 -> 10 (was the absolute lowest CPU priority) and cap
  ffmpeg to 6 threads on this 8-core host, leaving headroom for Mongo,
  the *arr stack, and the API itself instead of an unbounded encode.
- Add POST /transcode/queue/retry-failed to re-queue every failed/
  cancelled job at once; label the per-job Retry button with text
  (was icon-only) and clarify in the page copy that failed/cancelled
  jobs never delete the movie — retry just re-queues the same file.

backend/server.py

@@ -707,6 +707,16 @@ async def retry_job(job_id: str, user: dict = Depends(require_admin)):
     return {"ok": True, "job_id": new_job["id"]}
 
 
+@api.post("/transcode/queue/retry-failed")
+async def retry_all_failed(user: dict = Depends(require_admin)):
+    jobs = await db.transcode_queue.find({"status": {"$in": ["failed", "cancelled"]}}, {"_id": 0}).to_list(500)
+    retried = 0
+    for job in jobs:
+        await _enqueue_transcode(job["movie_id"], job["quality"], triggered_by=job.get("triggered_by", "manual"), content_type=job.get("content_type", "movie"))
+        retried += 1
+    return {"ok": True, "retried": retried}
+
+
 @api.post("/transcode/queue/clear")
 async def clear_finished(user: dict = Depends(require_admin)):
     res = await db.transcode_queue.delete_many({"status": {"$in": ["done", "failed", "cancelled"]}})

backend/transcode.py

@@ -13,6 +13,11 @@ from typing import Optional, List, Tuple, Callable, Awaitable
 
 logger = logging.getLogger("kino.transcode")
 
+# Moderate priority (was 19, the absolute lowest) and a thread cap so an ABR encode can't
+# starve the rest of the stack (Mongo, *arr apps, the API itself) on this 8-core host.
+TRANSCODE_NICE = 10
+TRANSCODE_THREADS = 6
+
 
 async def probe_video(source: Path) -> Tuple[int, int]:
     """Return (width, height) using ffprobe; (0, 0) on failure."""
@@ -58,7 +63,7 @@ async def transcode_quick(source: Path, out_dir: Path, on_status: Callable[...,
         return
     out_dir.mkdir(parents=True, exist_ok=True)
     cmd = [
-        "nice", "-n", "19",
+        "nice", "-n", str(TRANSCODE_NICE),
         "ffmpeg", "-y", "-i", str(source),
         "-c:v", "copy", "-c:a", "copy",
         "-bsf:v", "h264_mp4toannexb",
@@ -88,13 +93,14 @@ async def transcode_abr(source: Path, out_dir: Path, on_status: Callable[..., Aw
         fc_parts.append(f"[v{i}]scale=w=-2:h={h}[v{i}out]")
     filter_complex = ";".join(fc_parts)
 
-    cmd: List[str] = ["nice", "-n", "19", "ffmpeg", "-y", "-i", str(source), "-filter_complex", filter_complex]
+    cmd: List[str] = ["nice", "-n", str(TRANSCODE_NICE), "ffmpeg", "-y", "-threads", str(TRANSCODE_THREADS), "-i", str(source), "-filter_complex", filter_complex]
 
     for i, (_h, vb, maxr, buf, _ab) in enumerate(variants):
         cmd += [
             "-map", f"[v{i}out]",
             f"-c:v:{i}", "libx264",
             f"-preset:v:{i}", "veryfast",
+            f"-threads:v:{i}", str(TRANSCODE_THREADS),
             f"-profile:v:{i}", "main",
             f"-pix_fmt:v:{i}", "yuv420p",
             f"-b:v:{i}", vb,

frontend/src/pages/TranscodeQueue.jsx

@@ -44,6 +44,14 @@ export default function TranscodeQueue() {
     catch (err) { toast.error(err.response?.data?.detail || "Could not retry"); }
   };
 
+  const retryAllFailed = async () => {
+    try {
+      const { data } = await api.post("/transcode/queue/retry-failed");
+      toast.success(`Re-queued ${data.retried} job(s)`);
+      load();
+    } catch (err) { toast.error(err.response?.data?.detail || "Could not retry"); }
+  };
+
   const togglePause = async () => {
     try {
       const { data } = await api.post("/transcode/queue/pause", { paused: !stats.paused });
@@ -64,9 +72,9 @@ export default function TranscodeQueue() {
         <span className="text-xs uppercase tracking-[0.3em] text-[#D9381E]">Background</span>
         <h1 className="font-display text-5xl md:text-6xl font-black tracking-tighter text-white mt-3">Transcode Queue</h1>
         <p className="text-[#8A8A8A] mt-4 max-w-2xl">
-          One job runs at a time at low CPU priority. Auto-transcode is currently:{" "}
+          One job runs at a time, moderate CPU priority, capped threads so it can't starve the rest of the stack. Auto-transcode is currently:{" "}
           <span className="text-white">{stats.auto_transcode === "off" ? "off" : `auto · ${stats.auto_transcode}`}</span>
-          {" — "}<a href="/admin/settings" className="text-[#D9381E] hover:text-[#ED4B32]">change in Settings</a>
+          {" — "}<a href="/admin/settings" className="text-[#D9381E] hover:text-[#ED4B32]">change in Settings</a>. Failed and cancelled jobs never delete the movie — retry re-queues the same file.
         </p>
 
         <div className="mt-8 grid grid-cols-2 sm:grid-cols-5 gap-3">
@@ -86,6 +94,9 @@ export default function TranscodeQueue() {
             {stats.paused ? <PlayIcon size={14} strokeWidth={1.5} /> : <Pause size={14} strokeWidth={1.5} />}
             {stats.paused ? "Resume" : "Pause"}
           </button>
+          <button onClick={retryAllFailed} disabled={!stats.failed && !stats.cancelled} className="flex items-center gap-2 border border-[#222] hover:border-[#D9381E] hover:text-[#D9381E] text-[#8A8A8A] px-4 py-2 text-xs uppercase tracking-[0.2em] transition-colors disabled:opacity-50" data-testid="queue-retry-all">
+            <RotateCcw size={14} strokeWidth={1.5} /> Retry All Failed
+          </button>
           <button onClick={clearFinished} className="flex items-center gap-2 border border-[#222] hover:border-[#fca5a5] hover:text-[#fca5a5] text-[#8A8A8A] px-4 py-2 text-xs uppercase tracking-[0.2em] transition-colors" data-testid="queue-clear">
             <Trash2 size={14} strokeWidth={1.5} /> Clear Finished
           </button>
@@ -124,8 +135,8 @@ export default function TranscodeQueue() {
                   </button>
                 )}
                 {(j.status === "failed" || j.status === "cancelled") && (
-                  <button onClick={() => retry(j.id)} className="text-[#8A8A8A] hover:text-[#D9381E]" data-testid={`retry-${j.id}`} aria-label="Retry">
-                    <RotateCcw size={14} strokeWidth={1.5} />
+                  <button onClick={() => retry(j.id)} className="flex items-center gap-1 text-[10px] uppercase tracking-[0.2em] text-[#8A8A8A] hover:text-[#D9381E]" data-testid={`retry-${j.id}`}>
+                    <RotateCcw size={13} strokeWidth={1.5} /> Retry
                   </button>
                 )}
               </div>