feat: add chunk crossfade slider (0ms = hard cut)

Persisted setting (default 50ms) controls how audio chunks are blended
together.  Set to 0 for a clean hard cut with no overlap.

app/src/components/ServerSettings/ConnectionForm.tsx

@@ -36,6 +36,8 @@ export function ConnectionForm() {
   const setMode = useServerStore((state) => state.setMode);
   const maxChunkChars = useServerStore((state) => state.maxChunkChars);
   const setMaxChunkChars = useServerStore((state) => state.setMaxChunkChars);
+  const crossfadeMs = useServerStore((state) => state.crossfadeMs);
+  const setCrossfadeMs = useServerStore((state) => state.setCrossfadeMs);
   const { toast } = useToast();
 
   const form = useForm<ConnectionFormValues>({
@@ -177,6 +179,29 @@ export function ConnectionForm() {
               can improve quality for long outputs. Default is 800.
             </p>
           </div>
+
+          <div className="space-y-3 mt-4">
+            <div className="flex items-center justify-between">
+              <label htmlFor="crossfadeMs" className="text-sm font-medium leading-none">
+                Chunk crossfade
+              </label>
+              <span className="text-sm tabular-nums text-muted-foreground">
+                {crossfadeMs === 0 ? 'Cut' : `${crossfadeMs}ms`}
+              </span>
+            </div>
+            <Slider
+              id="crossfadeMs"
+              value={[crossfadeMs]}
+              onValueChange={([value]) => setCrossfadeMs(value)}
+              min={0}
+              max={200}
+              step={10}
+              aria-label="Chunk crossfade duration"
+            />
+            <p className="text-sm text-muted-foreground">
+              Blends audio between chunks to smooth transitions. Set to 0 for a hard cut.
+            </p>
+          </div>
         </div>
       </CardContent>
     </Card>

app/src/lib/api/types.ts

@@ -37,6 +37,7 @@ export interface GenerationRequest {
   engine?: 'qwen' | 'luxtts' | 'chatterbox' | 'chatterbox_turbo';
   instruct?: string;
   max_chunk_chars?: number;
+  crossfade_ms?: number;
 }
 
 export interface GenerationResponse {

app/src/lib/hooks/useGenerationForm.ts

@@ -33,6 +33,7 @@ export function useGenerationForm(options: UseGenerationFormOptions = {}) {
   const setAudioWithAutoPlay = usePlayerStore((state) => state.setAudioWithAutoPlay);
   const setIsGenerating = useGenerationStore((state) => state.setIsGenerating);
   const maxChunkChars = useServerStore((state) => state.maxChunkChars);
+  const crossfadeMs = useServerStore((state) => state.crossfadeMs);
   const [downloadingModelName, setDownloadingModelName] = useState<string | null>(null);
   const [downloadingDisplayName, setDownloadingDisplayName] = useState<string | null>(null);
 
@@ -113,6 +114,7 @@ export function useGenerationForm(options: UseGenerationFormOptions = {}) {
         engine,
         instruct: isQwen ? data.instruct || undefined : undefined,
         max_chunk_chars: maxChunkChars,
+        crossfade_ms: crossfadeMs,
       });
 
       toast({

app/src/stores/serverStore.ts

@@ -16,6 +16,9 @@ interface ServerStore {
 
   maxChunkChars: number;
   setMaxChunkChars: (value: number) => void;
+
+  crossfadeMs: number;
+  setCrossfadeMs: (value: number) => void;
 }
 
 export const useServerStore = create<ServerStore>()(
@@ -35,6 +38,9 @@ export const useServerStore = create<ServerStore>()(
 
       maxChunkChars: 800,
       setMaxChunkChars: (value) => set({ maxChunkChars: value }),
+
+      crossfadeMs: 50,
+      setCrossfadeMs: (value) => set({ crossfadeMs: value }),
     }),
     {
       name: 'voicebox-server',

backend/main.py

@@ -840,6 +840,7 @@ async def generate_speech(
             seed=data.seed,
             instruct=data.instruct,
             max_chunk_chars=data.max_chunk_chars,
+            crossfade_ms=data.crossfade_ms,
             trim_fn=trim_fn,
         )
 
@@ -970,6 +971,7 @@ async def stream_speech(
         seed=data.seed,
         instruct=data.instruct,
         max_chunk_chars=data.max_chunk_chars,
+        crossfade_ms=data.crossfade_ms,
         trim_fn=trim_fn,
     )
 

backend/models.py

@@ -59,6 +59,7 @@ class GenerationRequest(BaseModel):
     instruct: Optional[str] = Field(None, max_length=500)
     engine: Optional[str] = Field(default="qwen", pattern="^(qwen|luxtts|chatterbox|chatterbox_turbo)$")
     max_chunk_chars: int = Field(default=800, ge=100, le=5000, description="Max characters per chunk for long text splitting")
+    crossfade_ms: int = Field(default=50, ge=0, le=500, description="Crossfade duration in ms between chunks (0 for hard cut)")
 
 
 class GenerationResponse(BaseModel):

backend/utils/chunked_tts.py

@@ -224,6 +224,7 @@ async def generate_chunked(
     seed: int | None = None,
     instruct: str | None = None,
     max_chunk_chars: int = DEFAULT_MAX_CHUNK_CHARS,
+    crossfade_ms: int = 50,
     trim_fn=None,
 ) -> Tuple[np.ndarray, int]:
     """Generate audio with automatic chunking for long text.
@@ -234,7 +235,7 @@ async def generate_chunked(
     For longer text the input is split at natural sentence boundaries,
     each chunk is generated independently, optionally trimmed (useful for
     Chatterbox engines that hallucinate trailing noise), and the results
-    are concatenated with a short crossfade.
+    are concatenated with a crossfade (or hard cut if *crossfade_ms* is 0).
 
     Parameters
     ----------
@@ -246,6 +247,9 @@ async def generate_chunked(
         Forwarded to ``backend.generate()`` verbatim.
     max_chunk_chars : int
         Maximum characters per chunk (default 800).
+    crossfade_ms : int
+        Crossfade duration in milliseconds between chunks.  0 for a hard
+        cut with no overlap (default 50).
     trim_fn : callable | None
         Optional ``(audio, sample_rate) -> audio`` post-processing
         function applied to each chunk before concatenation (e.g.
@@ -294,5 +298,5 @@ async def generate_chunked(
         if sample_rate is None:
             sample_rate = chunk_sr
 
-    audio = concatenate_audio_chunks(audio_chunks, sample_rate)
+    audio = concatenate_audio_chunks(audio_chunks, sample_rate, crossfade_ms=crossfade_ms)
     return audio, sample_rate