fix(avhw): handle tx.send() failure and pause encoding on WebRTC disconnect (closes #6)

- Replace 'let _ = tx.send()' with proper error handling: log warning,
  set webrtc_disconnected flag, and break drain loop on SendError
- Add Arc<AtomicBool> webrtc_paused shared between State/StatePortal
  and SwEncState, synced from wrtc.is_connected() in poll_webrtc()
- Skip encoding in encode_filtered_frame() when paused or disconnected
- Drain and discard stale channel frames on disconnect
- Resume encoding automatically on WebRTC reconnection

src/avhw.rs

@@ -3,6 +3,8 @@ use std::mem;
 use std::os::fd::{AsRawFd, RawFd};
 use std::os::raw::c_void;
 use std::path::Path;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
 use std::ptr;
 
 use anyhow::{bail, Result};
@@ -611,6 +613,8 @@ pub struct SwEncState {
     yuv_frame: *mut ffi::AVFrame,
     starting_timestamp: Option<i64>,
     frames_written: bool,
+    webrtc_disconnected: bool,
+    webrtc_paused: Option<Arc<AtomicBool>>,
 }
 
 unsafe impl Send for SwEncState {}
@@ -660,6 +664,8 @@ impl SwEncState {
             yuv_frame,
             starting_timestamp: None,
             frames_written: false,
+            webrtc_disconnected: false,
+            webrtc_paused: None,
         })
     }
 
@@ -674,6 +680,7 @@ impl SwEncState {
         bitrate: u64,
         gop_size: u32,
         tx: crossbeam_channel::Sender<Vec<u8>>,
+        webrtc_paused: Arc<AtomicBool>,
     ) -> Result<Self> {
         tracing::info!(
             "SwEncState::new_webrtc: GPU downscale {width}x{height} BGRA -> {enc_width}x{enc_height} NV12, software H.264 -> WebRTC"
@@ -705,6 +712,8 @@ impl SwEncState {
             yuv_frame,
             starting_timestamp: None,
             frames_written: false,
+            webrtc_disconnected: false,
+            webrtc_paused: Some(webrtc_paused),
         })
     }
 
@@ -774,6 +783,14 @@ impl SwEncState {
     }
 
     fn encode_filtered_frame(&mut self, filtered: &ff::frame::Video) -> Result<()> {
+        if self.webrtc_disconnected {
+            return Ok(());
+        }
+        if let Some(ref paused) = self.webrtc_paused {
+            if paused.load(Ordering::Relaxed) {
+                return Ok(());
+            }
+        }
         let mut sw_nv12 = unsafe { ffi::av_frame_alloc() };
         if sw_nv12.is_null() {
             bail!("av_frame_alloc failed for NV12 transfer frame");
@@ -876,7 +893,14 @@ impl SwEncState {
                         let data: &[u8] = unsafe {
                             std::slice::from_raw_parts(raw.data, raw.size as usize)
                         };
-                        let _ = tx.send(data.to_vec());
+                        if let Err(e) = tx.send(data.to_vec()) {
+                            tracing::warn!(
+                                "WebRTC channel send failed (receiver dropped): {} bytes lost",
+                                e.0.len()
+                            );
+                            self.webrtc_disconnected = true;
+                            break;
+                        }
                     }
                 }
                 None => {}