fix ndi->decklinkout slowdown

nodes/ndiin/main.cpp

@@ -1,3 +1,4 @@
+#include <chrono>
 #include <cstring>
 #include <string>
 #include <vector>
@@ -96,19 +97,23 @@ class NDIInNode : public dmf::NodeBase {
         dmf::NDIReceiver::AudioInfo audio_info;
 
         while (dmf::g_running.load(std::memory_order_relaxed)) {
-            // Drain all queued NDI frames before writing one MXL grain.
+            // Drain available NDI frames before writing one MXL grain.
             // With audio enabled, many audio packets may be queued ahead of a video frame.
-            // Calling capture() once per grain window would starve video reception.
-            // Strategy: blocking first call (5ms), then non-blocking drain of remainder.
+            // Budget: drain for at most half a frame period so the grain clock stays on time
+            // even when catching up from a startup audio backlog.
             try {
+                const auto drain_deadline =
+                    std::chrono::steady_clock::now() + std::chrono::milliseconds(20);
                 bool first = true;
-                while (dmf::g_running.load(std::memory_order_relaxed)) {
+                while (dmf::g_running.load(std::memory_order_relaxed) &&
+                       std::chrono::steady_clock::now() < drain_deadline) {
                     auto kind = ndi.capture(latest_video.data(), video_stride,
                                             audio_buf, audio_info, has_audio,
                                             first ? 5 : 0);
                     first = false;
                     if (kind == dmf::NDIReceiver::FrameKind::Video) {
                         have_video = true;
+                        break;  // got video — write grain now, remaining audio deferred to next window
                     } else if (kind == dmf::NDIReceiver::FrameKind::Audio && has_audio) {
                         mxlMutableWrappedMultiBufferSlice slice{};
                         if (mxlFlowWriterOpenSamples(audio_writer, audio_index,