good checkpoint

media/client/src/backends/subprocess.rs

@@ -66,6 +66,25 @@ pub fn run(
     // Keep stdout alive for the duration of demuxing.
     let _stdout_guard = stdout;
 
+    // Watch for stop flag on a separate thread and kill ffmpeg to unblock
+    // the packet iterator (which is a blocking read on the pipe fd).
+    let stop_watcher = stop.clone();
+    let child_pid = child.id();
+    std::thread::Builder::new()
+        .name("ffmpeg-stop-watcher".into())
+        .spawn(move || {
+            while !stop_watcher.load(Ordering::Relaxed) {
+                std::thread::sleep(std::time::Duration::from_millis(100));
+            }
+            // Send SIGINT to ffmpeg so it flushes and closes stdout,
+            // which unblocks the packet iterator in demux_and_send.
+            use nix::sys::signal::{kill, Signal};
+            use nix::unistd::Pid;
+            let _ = kill(Pid::from_raw(child_pid as i32), Signal::SIGINT);
+            info!("Stop watcher: sent SIGINT to ffmpeg pid={child_pid}");
+        })
+        .expect("spawn stop watcher");
+
     let result = demux_and_send(fd, packet_tx, stop, &mut child);
 
     // Clean up subprocess regardless of result.