diff --git a/internal/subtitles/ai/service.go b/internal/subtitles/ai/service.go
index e7d773f9..ffbacf49 100644
--- a/internal/subtitles/ai/service.go
+++ b/internal/subtitles/ai/service.go
@@ -279,6 +279,14 @@ func (s *Service) dispatch(job Job) {
 			cancel()
 		}()
 
+		// Heartbeat for the whole lifetime — crucially including while queued
+		// behind the semaphore — so the stale-job reaper never reaps a job that is
+		// alive but merely waiting for a slot (which would otherwise mark it failed
+		// and let it resurrect itself on acquire, or admit a duplicate).
+		stopHeartbeat := make(chan struct{})
+		defer close(stopHeartbeat)
+		go s.heartbeatLoop(runCtx, job.ID, stopHeartbeat)
+
 		// Bound concurrency so translation never starves transcodes.
 		select {
 		case s.sem <- struct{}{}:
@@ -292,27 +300,25 @@ func (s *Service) dispatch(job Job) {
 	}()
 }
 
-func (s *Service) run(ctx context.Context, job *Job) {
-	// Keep heartbeat_at fresh while the job runs (progress updates also bump it),
-	// so the stale-job reaper never resets a job that is still alive during a long
-	// single LLM call.
-	stopHeartbeat := make(chan struct{})
-	defer close(stopHeartbeat)
-	go func() {
-		ticker := time.NewTicker(heartbeatInterval)
-		defer ticker.Stop()
-		for {
-			select {
-			case <-stopHeartbeat:
-				return
-			case <-ctx.Done():
-				return
-			case <-ticker.C:
-				_ = s.repo.Heartbeat(context.WithoutCancel(ctx), job.ID)
-			}
+// heartbeatLoop keeps a job's heartbeat_at fresh until the job ends or the
+// context is cancelled, so the stale-job reaper only ever reaps jobs orphaned by
+// a crashed worker.
+func (s *Service) heartbeatLoop(ctx context.Context, jobID int64, stop <-chan struct{}) {
+	ticker := time.NewTicker(heartbeatInterval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-stop:
+			return
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			_ = s.repo.Heartbeat(context.WithoutCancel(ctx), jobID)
 		}
-	}()
+	}
+}
 
+func (s *Service) run(ctx context.Context, job *Job) {
 	if err := s.repo.UpdateProgress(ctx, job.ID, JobStatusRunning, 0, "Loading subtitle"); err != nil {
 		s.logger.Warn("failed to mark subtitle ai job running", "job", job.ID, "error", err)
 	}
diff --git a/web/src/pages/admin-settings/IntegrationsSettings.tsx b/web/src/pages/admin-settings/IntegrationsSettings.tsx
index 2088e3e7..ce49d782 100644
--- a/web/src/pages/admin-settings/IntegrationsSettings.tsx
+++ b/web/src/pages/admin-settings/IntegrationsSettings.tsx
@@ -536,6 +536,9 @@ function AISubtitleTranslationCard() {
         <Button type="button" onClick={save} disabled={updateSetting.isPending}>
           {updateSetting.isPending ? "Saving..." : "Save AI Translation Settings"}
         </Button>
+        <p className="text-muted-foreground mt-2 text-xs">
+          Changes take effect after a server restart.
+        </p>
       </div>
     </div>
   );
diff --git a/web/src/player/components/SubtitleTranslateModal.test.ts b/web/src/player/components/SubtitleTranslateModal.test.ts
new file mode 100644
index 00000000..a1510887
--- /dev/null
+++ b/web/src/player/components/SubtitleTranslateModal.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { isTranslatableSource } from "./SubtitleTranslateModal";
+import type { PlayerSubtitleInfo } from "../types";
+
+function track(p: Partial<PlayerSubtitleInfo>): PlayerSubtitleInfo {
+  return { index: 0, language: "en", label: "", url: "", ...p };
+}
+
+describe("isTranslatableSource", () => {
+  it("accepts text external/downloaded subtitles", () => {
+    expect(isTranslatableSource(track({ source: "external", codec: "srt" }))).toBe(true);
+    expect(isTranslatableSource(track({ source: "downloaded", codec: "subrip" }))).toBe(true);
+    expect(isTranslatableSource(track({ source: "external", codec: "vtt" }))).toBe(true);
+  });
+
+  it("rejects ASS/SSA external/downloaded subtitles the server can't parse", () => {
+    expect(isTranslatableSource(track({ source: "external", codec: "ass" }))).toBe(false);
+    expect(isTranslatableSource(track({ source: "downloaded", codec: "ssa" }))).toBe(false);
+  });
+
+  it("accepts non-bitmap embedded tracks (extracted via ffmpeg, incl. ASS)", () => {
+    expect(isTranslatableSource(track({ source: "embedded", codec: "ass" }))).toBe(true);
+    expect(isTranslatableSource(track({ source: "embedded", codec: "subrip" }))).toBe(true);
+  });
+
+  it("rejects bitmap embedded tracks", () => {
+    expect(isTranslatableSource(track({ source: "embedded", codec: "hdmv_pgs_subtitle" }))).toBe(
+      false,
+    );
+    expect(isTranslatableSource(track({ source: "embedded", codec: "dvd_subtitle" }))).toBe(false);
+  });
+
+  it("rejects the in-progress live track", () => {
+    expect(isTranslatableSource(track({ source: "downloaded", codec: "srt", live: true }))).toBe(
+      false,
+    );
+  });
+});
diff --git a/web/src/player/components/SubtitleTranslateModal.tsx b/web/src/player/components/SubtitleTranslateModal.tsx
index 350aa6a1..b702bced 100644
--- a/web/src/player/components/SubtitleTranslateModal.tsx
+++ b/web/src/player/components/SubtitleTranslateModal.tsx
@@ -1,10 +1,29 @@
 import { useState, useEffect, useCallback, useMemo } from "react";
 import { createPortal } from "react-dom";
+import { toast } from "sonner";
 import type { PlayerConfig } from "../context/PlayerConfigContext";
 import type { PlayerSubtitleInfo } from "../types";
 import { playerFetch } from "../player-fetch";
 import { LANGUAGES, getLanguageName } from "../utils/languageNames";
 
+// Formats the server can parse directly from an external/downloaded file.
+const TRANSLATABLE_TEXT_CODECS = new Set(["srt", "subrip", "vtt", "webvtt"]);
+// Bitmap codecs the server can't extract as text (it would burn them in).
+const BITMAP_CODECS = new Set(["pgs", "hdmv_pgs_subtitle", "dvd_subtitle", "dvb_subtitle"]);
+
+// Mirror the server's loadSource acceptance: embedded non-bitmap tracks are
+// extracted to text via ffmpeg, while external/downloaded sources must already
+// be a parseable text format. Offering anything else starts a job that fails
+// asynchronously instead of preventing the choice up front.
+export function isTranslatableSource(track: PlayerSubtitleInfo): boolean {
+  if (track.live) return false;
+  const codec = (track.codec ?? "").toLowerCase();
+  if (track.source === "embedded") {
+    return !BITMAP_CODECS.has(codec);
+  }
+  return TRANSLATABLE_TEXT_CODECS.has(codec);
+}
+
 interface SubtitleTranslateModalProps {
   mediaFileId: number;
   playerConfig: PlayerConfig;
@@ -30,8 +49,9 @@ export function SubtitleTranslateModal({
   getStartPosition,
   onClose,
 }: SubtitleTranslateModalProps) {
-  // Live (in-progress) tracks can't be a translation source.
-  const sourceTracks = useMemo(() => tracks.filter((t) => !t.live), [tracks]);
+  // Only offer sources the server can actually translate (excludes live tracks,
+  // bitmap embedded tracks, and ASS/non-text external/downloaded tracks).
+  const sourceTracks = useMemo(() => tracks.filter(isTranslatableSource), [tracks]);
   const [sourceIndex, setSourceIndex] = useState<number | null>(null);
   const [targetLang, setTargetLang] = useState("en");
   const [submitting, setSubmitting] = useState(false);
@@ -54,18 +74,30 @@ export function SubtitleTranslateModal({
     setSubmitting(true);
     setError(null);
     try {
-      await playerFetch(playerConfig, "/subtitles/ai/translate", {
-        method: "POST",
-        body: JSON.stringify({
-          media_file_id: mediaFileId,
-          source_index: effectiveSourceIndex,
-          source_language: source?.language ?? "",
-          target_language: targetLang,
-          session_id: sessionId ?? "",
-          start_position: getStartPosition?.() ?? 0,
-        }),
-      });
-      // The player takes over from here: it pauses, streams cues in as they're
+      const res = await playerFetch<{ job?: { status?: string } }>(
+        playerConfig,
+        "/subtitles/ai/translate",
+        {
+          method: "POST",
+          body: JSON.stringify({
+            media_file_id: mediaFileId,
+            source_index: effectiveSourceIndex,
+            source_language: source?.language ?? "",
+            target_language: targetLang,
+            session_id: sessionId ?? "",
+            start_position: getStartPosition?.() ?? 0,
+          }),
+        },
+      );
+      // A request that collapses onto an already-running job (e.g. after a
+      // reload, or a second viewer) won't get its own live stream — tell the
+      // user it's underway; it'll appear via the subtitle-ready refresh.
+      if (res?.job?.status === "running") {
+        toast.info(
+          "A translation for this track is already in progress — it'll appear when it's ready.",
+        );
+      }
+      // Otherwise the player takes over: it pauses, streams cues in as they're
       // translated, then resumes once your position is covered.
       onClose();
     } catch (err) {