fix bad audio quality & save_to_disk example (#64)

- save_to_disk example: write raw pcm frames into a wav file

livekit-ffi/src/server/audio_frame.rs

@@ -62,7 +62,7 @@ impl FfiAudioSream {
                     close_tx,
                     track_sid,
                 };
-                tokio::spawn(Self::native_audio_stream_task(
+                server.async_runtime.spawn(Self::native_audio_stream_task(
                     server,
                     audio_stream.handle_id,
                     NativeAudioStream::new(track),

livekit-ffi/src/server/mod.rs

@@ -200,7 +200,7 @@ impl FfiServer {
         publish: proto::PublishTrackRequest,
     ) -> FfiResult<proto::PublishTrackResponse> {
         let async_id = self.next_id() as FfiAsyncId;
-        tokio::spawn(async move {
+        self.async_runtime.spawn(async move {
             let res = async {
                 let room_handle = publish
                     .room_handle

livekit-ffi/src/server/room.rs

@@ -21,7 +21,7 @@ impl FfiRoom {
         let session = room.session();
         let next_id = server.next_id() as FfiHandleId;
 
-        let handle = tokio::spawn(room_task(
+        let handle = server.async_runtime.spawn(room_task(
             server,
             session.clone(),
             next_id,
@@ -60,9 +60,11 @@ async fn room_task(
     mut events: mpsc::UnboundedReceiver<livekit::RoomEvent>,
     mut close_rx: oneshot::Receiver<()>,
 ) {
-    tokio::spawn(participant_task(Participant::Local(
-        session.local_participant(),
-    )));
+    server
+        .async_runtime
+        .spawn(participant_task(Participant::Local(
+            session.local_participant(),
+        )));
 
     loop {
         tokio::select! {
@@ -73,7 +75,7 @@ async fn room_task(
 
                 match event {
                     RoomEvent::ParticipantConnected(p) => {
-                        tokio::spawn(participant_task(Participant::Remote(p)));
+                        server.async_runtime.spawn(participant_task(Participant::Remote(p)));
                     }
                     _ => {}
                 }

livekit-ffi/src/server/video_frame.rs

@@ -62,7 +62,7 @@ impl FfiVideoStream {
                     stream_type,
                     track_sid,
                 };
-                tokio::spawn(Self::native_video_stream_task(
+                server.async_runtime.spawn(Self::native_video_stream_task(
                     server,
                     video_stream.handle_id,
                     NativeVideoStream::new(track),