diff --git a/agent/src/capture.rs b/agent/src/capture.rs
index 48c2858..d6e141e 100644
--- a/agent/src/capture.rs
+++ b/agent/src/capture.rs
@@ -201,7 +201,8 @@ impl NvencEncoder {
         // CBR 桌面实时档：码率恒定，延迟可预测（对标 UU 3.2Mbps@60fps）
         config.preset_cfg.rc_params.rate_control_mode = NVencParamsRcMode::CBR;
         config.preset_cfg.rc_params.average_bit_rate = bitrate_bps;
-        config.preset_cfg.gop_len = 0xffff_ffff; // 无周期 IDR，仅按需（KeyFrameReq）
+        config.preset_cfg.gop_len = 240; // 周期 IDR（60fps 下 4s）：网络异常后的自愈恢复点，
+                                         // 配合 KeyFrameReq 即时恢复，避免长时间冻结
         config.preset_cfg.frame_interval_p = 1; // 无 B 帧
 
         let init = InitParams {
diff --git a/viewer/src/main.rs b/viewer/src/main.rs
index 1ef5d90..2a1103e 100644
--- a/viewer/src/main.rs
+++ b/viewer/src/main.rs
@@ -241,13 +241,20 @@ fn session(
     let (w, h) = (width as usize, height as usize);
     let stats = Arc::new(Stats::default());
 
-    // 读任务（流 1）：H.264 解码 → RGB → mpsc；同时统计端到端延迟与流量
-    let (frame_tx, frame_rx) = std::sync::mpsc::channel::<Vec<u8>>();
+    // 读任务（流 1）：H.264 解码 → RGB → 单槽 latest-wins；同时统计端到端延迟与流量
+    // 帧格式 (src_w, src_h, rgb)；(0,0,_) = 解码失败占位，触发 KeyFrameReq
+    // 单槽而非无界队列：渲染跟不上 60fps 到达率时旧帧直接被覆盖，绝不积压
+    //（无界 mpsc 在 NVENC 60fps 下会无限积压 → 延迟线性增长 + 渲染 drain 时
+    //  长时间阻塞窗口消息泵 → 窗口假死、HUD 停刷新）
+    let latest: Arc<std::sync::Mutex<Option<(u32, u32, Vec<u8>)>>> =
+        Arc::new(std::sync::Mutex::new(None));
     {
         let stats = stats.clone();
+        let latest = latest.clone();
         let mut decoder = openh264::decoder::Decoder::new()
             .map_err(|e| anyhow::anyhow!("decoder init failed: {e}"))?;
         tokio::spawn(async move {
+            let mut size_logged = false;
             loop {
                 match common::read_video_frame(&mut recv).await {
                     Ok((hdr, payload)) => {
@@ -275,10 +282,19 @@ fn session(
                         match decoder.decode(&payload) {
                             Ok(Some(yuv)) => {
                                 let (dw, dh) = yuv.dimensions();
-                                let mut rgb = vec![0u8; dw * dh * 3];
+                                let (dw, dh) = (dw as u32, dh as u32);
+                                if !size_logged {
+                                    size_logged = true;
+                                    eprintln!(
+                                        "[viewer] decoded frame {dw}x{dh} (window {}x{})",
+                                        hdr.width, hdr.height
+                                    );
+                                }
+                                let mut rgb = vec![0u8; dw as usize * dh as usize * 3];
                                 yuv.write_rgb8(&mut rgb);
-                                if frame_tx.send(rgb).is_err() {
-                                    break;
+                                // latest-wins：直接覆盖旧帧，无积压
+                                if let Ok(mut slot) = latest.lock() {
+                                    *slot = Some((dw, dh, rgb));
                                 }
                             }
                             Ok(None) => {}
@@ -286,7 +302,9 @@ fn session(
                                 // 解码异常：请求被控端强制关键帧
                                 stats.dec_fail.fetch_add(1, Ordering::Relaxed);
                                 eprintln!("[viewer] decode failed: {e}, request keyframe");
-                                let _ = frame_tx.send(Vec::new()); // 空帧占位唤醒渲染循环
+                                if let Ok(mut slot) = latest.lock() {
+                                    *slot = Some((0, 0, Vec::new()));
+                                }
                             }
                         }
                     }
@@ -379,18 +397,15 @@ fn session(
             push(&msg_tx, ControlMsg::Ping(now_ms()));
         }
 
-        // 1) 渲染最新帧（只保留最新，丢弃积压）；空帧=解码异常，请求关键帧
-        loop {
-            match frame_rx.try_recv() {
-                Ok(raw) => {
-                    if raw.is_empty() {
-                        push(&msg_tx, ControlMsg::KeyFrameReq);
-                    } else if raw.len() == w * h * 3 {
-                        blit(&mut buffer, &raw);
-                        dirty = true;
-                    }
+        // 1) 渲染最新帧（单槽 latest-wins：每迭代只取最新一帧，天然防积压）
+        if let Ok(mut slot) = latest.lock() {
+            if let Some((sw, sh, raw)) = slot.take() {
+                if raw.is_empty() {
+                    push(&msg_tx, ControlMsg::KeyFrameReq);
+                } else if sw > 0 && sh > 0 {
+                    blit(&mut buffer, w, h, &raw, sw as usize, sh as usize);
+                    dirty = true;
                 }
-                Err(_) => break,
             }
         }
 
@@ -675,9 +690,17 @@ fn draw_hud(buffer: &mut [u32], w: usize, lines: &[(&str, &str, u32)]) {
     }
 }
 
-/// RGB888 字节（openh264 解码输出）→ minifb 0RGB u32 缓冲
-fn blit(buffer: &mut [u32], raw: &[u8]) {
-    for (px, chunk) in buffer.iter_mut().zip(raw.chunks_exact(3)) {
-        *px = ((chunk[0] as u32) << 16) | ((chunk[1] as u32) << 8) | chunk[2] as u32;
+/// RGB888 字节（openh264 解码输出）→ minifb 0RGB u32 缓冲。
+/// 支持源尺寸与窗口不同（解码器可能对齐到 16 倍数，如 1080→1088）：
+/// 逐行拷贝重叠区域，源小于窗口时右侧/下方留黑。
+fn blit(buffer: &mut [u32], w: usize, h: usize, raw: &[u8], dw: usize, dh: usize) {
+    let cw = w.min(dw);
+    let ch = h.min(dh);
+    for row in 0..ch {
+        let src = &raw[row * dw * 3..row * dw * 3 + cw * 3];
+        let dst = &mut buffer[row * w..row * w + cw];
+        for (px, chunk) in dst.iter_mut().zip(src.chunks_exact(3)) {
+            *px = ((chunk[0] as u32) << 16) | ((chunk[1] as u32) << 8) | chunk[2] as u32;
+        }
     }
 }