fix: 优化视频切换流畅性；修复 OTG HID 功能无法一次保存成功和页面未即刻生效问题

src/config/store.rs

@@ -4,6 +4,7 @@ use std::path::Path;
 use std::sync::Arc;
 use std::time::Duration;
 use tokio::sync::broadcast;
+use tokio::sync::Mutex;
 
 use super::AppConfig;
 use crate::error::{AppError, Result};
@@ -18,6 +19,8 @@ pub struct ConfigStore {
     /// Lock-free cache using ArcSwap for zero-cost reads
     cache: Arc<ArcSwap<AppConfig>>,
     change_tx: broadcast::Sender<ConfigChange>,
+    /// Serializes `set` / `update` so concurrent PATCH handlers cannot clobber each other
+    write_lock: Arc<Mutex<()>>,
 }
 
 /// Configuration change event
@@ -59,6 +62,7 @@ impl ConfigStore {
             pool,
             cache,
             change_tx,
+            write_lock: Arc::new(Mutex::new(())),
         })
     }
 
@@ -191,6 +195,7 @@ impl ConfigStore {
 
     /// Set entire configuration
     pub async fn set(&self, config: AppConfig) -> Result<()> {
+        let _guard = self.write_lock.lock().await;
         Self::save_config_to_db(&self.pool, &config).await?;
         self.cache.store(Arc::new(config));
 
@@ -204,13 +209,13 @@ impl ConfigStore {
 
     /// Update configuration with a closure
     ///
-    /// Note: This uses a read-modify-write pattern. For concurrent updates,
-    /// the last write wins. This is acceptable for configuration changes
-    /// which are infrequent and typically user-initiated.
+    /// Uses read-modify-write under a mutex so concurrent `update` / `set` calls are serialized
+    /// and merged correctly (each closure sees the latest stored config).
     pub async fn update<F>(&self, f: F) -> Result<()>
     where
         F: FnOnce(&mut AppConfig),
     {
+        let _guard = self.write_lock.lock().await;
         // Load current config, clone it for modification
         let current = self.cache.load();
         let mut config = (**current).clone();

src/video/shared_video_pipeline.rs

@@ -844,7 +844,7 @@ impl SharedVideoPipeline {
         }
     }
 
-    /// Stop the pipeline
+    /// Stop the pipeline (non-blocking, does not wait for capture thread to exit)
     pub fn stop(&self) {
         if *self.running_rx.borrow() {
             let _ = self.running.send(false);
@@ -854,6 +854,39 @@ impl SharedVideoPipeline {
         }
     }
 
+    /// Stop the pipeline and wait for the capture thread to fully exit.
+    ///
+    /// This ensures the V4L2 device is released before returning, which is
+    /// necessary when another consumer (e.g. MJPEG streamer) needs to open
+    /// the same device immediately after.
+    pub async fn stop_and_wait(&self, timeout: std::time::Duration) {
+        self.stop();
+        let mut rx = self.running_watch();
+        if !*rx.borrow() {
+            // Capture thread may still be running from a previous `stop()` call.
+            // Wait for the "Video pipeline stopped" log (thread sets running=false
+            // at exit), unless it already happened.
+        }
+        let deadline = tokio::time::Instant::now() + timeout;
+        loop {
+            if !self.running_flag.load(Ordering::Acquire) {
+                // Flag is cleared, but the capture thread may still be unwinding
+                // (dropping the V4L2 stream). Give it a brief moment.
+                tokio::time::sleep(std::time::Duration::from_millis(50)).await;
+                break;
+            }
+            let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+            if remaining.is_zero() {
+                warn!(
+                    "Timed out waiting for video pipeline to stop after {:?}",
+                    timeout
+                );
+                break;
+            }
+            let _ = tokio::time::timeout(remaining, rx.changed()).await;
+        }
+    }
+
     /// Set bitrate using preset
     pub async fn set_bitrate_preset(
         &self,

src/video/stream_manager.rs

@@ -404,8 +404,11 @@ impl VideoStreamManager {
                 }
             }
             StreamMode::WebRTC => {
-                info!("Closing all WebRTC sessions");
-                let closed = self.webrtc_streamer.close_all_sessions().await;
+                info!("Closing all WebRTC sessions and releasing capture device");
+                let closed = self
+                    .webrtc_streamer
+                    .close_all_sessions_and_release_device()
+                    .await;
                 if closed > 0 {
                     info!("Closed {} WebRTC sessions", closed);
                 }
@@ -781,6 +784,61 @@ impl VideoStreamManager {
         self.webrtc_streamer.request_keyframe().await
     }
 
+    /// Notify frontend about a codec-only switch (WebRTC mode unchanged, codec changed).
+    ///
+    /// `set_video_codec` already rebuilt the pipeline synchronously, so we just
+    /// emit the events the frontend waits on: `StreamModeChanged`, `WebRTCReady`,
+    /// and `StreamModeReady`.
+    ///
+    /// Events are spawned asynchronously so the HTTP response (carrying the
+    /// `transition_id`) reaches the client before the WebSocket events, giving
+    /// the frontend time to call `registerTransition()` first.
+    pub async fn notify_codec_switch(
+        self: &Arc<Self>,
+        transition_id: &str,
+        new_codec_str: &str,
+        previous_codec_str: &str,
+    ) {
+        let manager = Arc::clone(self);
+        let transition_id = transition_id.to_string();
+        let new_codec = new_codec_str.to_string();
+        let prev_codec = previous_codec_str.to_string();
+
+        tokio::spawn(async move {
+            // Small yield to ensure the HTTP response is flushed first.
+            tokio::task::yield_now().await;
+
+            manager
+                .publish_event(SystemEvent::StreamModeChanged {
+                    transition_id: Some(transition_id.clone()),
+                    mode: new_codec.clone(),
+                    previous_mode: prev_codec.clone(),
+                })
+                .await;
+
+            let is_hardware = manager.webrtc_streamer.is_hardware_encoding().await;
+            manager
+                .publish_event(SystemEvent::WebRTCReady {
+                    transition_id: Some(transition_id.clone()),
+                    codec: new_codec.clone(),
+                    hardware: is_hardware,
+                })
+                .await;
+
+            manager
+                .publish_event(SystemEvent::StreamModeReady {
+                    transition_id: transition_id.clone(),
+                    mode: new_codec.clone(),
+                })
+                .await;
+
+            info!(
+                "Codec switch notified: {} -> {} (transition: {})",
+                prev_codec, new_codec, transition_id
+            );
+        });
+    }
+
     /// Publish event to event bus
     async fn publish_event(&self, event: SystemEvent) {
         if let Some(ref events) = *self.events.read().await {

src/web/handlers/mod.rs

@@ -1282,7 +1282,26 @@ pub async fn stream_mode_set(
         }
     }
 
-    // Set video codec if switching to WebRTC mode with specific codec
+    let requested_mode_str = match (&new_mode, &video_codec) {
+        (StreamMode::Mjpeg, _) => "mjpeg",
+        (StreamMode::WebRTC, Some(VideoCodecType::H264)) => "h264",
+        (StreamMode::WebRTC, Some(VideoCodecType::H265)) => "h265",
+        (StreamMode::WebRTC, Some(VideoCodecType::VP8)) => "vp8",
+        (StreamMode::WebRTC, Some(VideoCodecType::VP9)) => "vp9",
+        (StreamMode::WebRTC, None) => "webrtc",
+    };
+
+    // Detect codec-only switch: already in WebRTC mode, just changing codec.
+    // switch_mode_transaction treats this as "no switch needed" since StreamMode
+    // is still WebRTC, so we handle codec change + event emission here.
+    let current_mode = state.stream_manager.current_mode().await;
+    let prev_codec = state.stream_manager.webrtc_streamer().current_video_codec().await;
+
+    let codec_changed = video_codec.is_some_and(|c| c != prev_codec);
+    let is_codec_only_switch = current_mode == StreamMode::WebRTC
+        && new_mode == StreamMode::WebRTC
+        && codec_changed;
+
     if let Some(codec) = video_codec {
         info!("Setting WebRTC video codec to {:?}", codec);
         if let Err(e) = state
@@ -1295,22 +1314,34 @@ pub async fn stream_mode_set(
         }
     }
 
+    // For codec-only switch, emit events directly instead of going through
+    // switch_mode_transaction (which short-circuits when mode is unchanged).
+    if is_codec_only_switch {
+        let transition_id = uuid::Uuid::new_v4().to_string();
+
+        state
+            .stream_manager
+            .notify_codec_switch(
+                &transition_id,
+                requested_mode_str,
+                &codec_to_id(prev_codec),
+            )
+            .await;
+
+        return Ok(Json(StreamModeResponse {
+            success: true,
+            mode: requested_mode_str.to_string(),
+            transition_id: Some(transition_id),
+            switching: false,
+            message: Some(format!("Codec switched to {}", requested_mode_str)),
+        }));
+    }
+
     let tx = state
         .stream_manager
         .switch_mode_transaction(new_mode.clone())
         .await?;
 
-    // Return the requested codec identifier (for UI display). The actual active mode
-    // may differ if the request was rejected due to an in-progress switch.
-    let requested_mode_str = match (&new_mode, &video_codec) {
-        (StreamMode::Mjpeg, _) => "mjpeg",
-        (StreamMode::WebRTC, Some(VideoCodecType::H264)) => "h264",
-        (StreamMode::WebRTC, Some(VideoCodecType::H265)) => "h265",
-        (StreamMode::WebRTC, Some(VideoCodecType::VP8)) => "vp8",
-        (StreamMode::WebRTC, Some(VideoCodecType::VP9)) => "vp9",
-        (StreamMode::WebRTC, None) => "webrtc",
-    };
-
     let active_mode_str = match state.stream_manager.current_mode().await {
         StreamMode::Mjpeg => "mjpeg".to_string(),
         StreamMode::WebRTC => {

src/webrtc/webrtc_streamer.rs

@@ -787,6 +787,22 @@ impl WebRtcStreamer {
         count
     }
 
+    /// Close all sessions and wait for the video pipeline to fully release the
+    /// capture device. Use this when the caller needs the V4L2 device immediately
+    /// afterwards (e.g. switching to MJPEG mode).
+    pub async fn close_all_sessions_and_release_device(&self) -> usize {
+        let count = self.close_all_sessions().await;
+
+        if let Some(ref pipeline) = *self.video_pipeline.read().await {
+            pipeline
+                .stop_and_wait(std::time::Duration::from_secs(3))
+                .await;
+        }
+        *self.video_pipeline.write().await = None;
+
+        count
+    }
+
     /// Get session count
     pub async fn session_count(&self) -> usize {
         self.sessions.read().await.len()