Read info about source from source/flow_def

shared/NDIReceiver.hpp

@@ -121,6 +121,39 @@ public:
         int channel_stride = 0;  // floats between channel planes (NDI planar layout)
     };
 
+    // Waits for the first audio packet and returns its format.
+    // Call after probe(). Audio packets are typically already queued at that point.
+    // Discards any video frames encountered while searching. Respects g_running.
+    AudioInfo probe_audio(uint32_t timeout_ms = 5000) {
+        const auto deadline = std::chrono::steady_clock::now()
+                              + std::chrono::milliseconds(timeout_ms);
+        while (dmf::g_running.load(std::memory_order_relaxed) &&
+               std::chrono::steady_clock::now() < deadline) {
+            NDIlib_video_frame_v2_t video_frame{};
+            NDIlib_audio_frame_v3_t audio_frame{};
+            auto type = NDIlib_recv_capture_v3(recv_, &video_frame, &audio_frame, nullptr, 100);
+            if (type == NDIlib_frame_type_error)
+                throw std::runtime_error("NDI source lost during audio probe");
+            if (type == NDIlib_frame_type_video) {
+                NDIlib_recv_free_video_v2(recv_, &video_frame);
+                continue;
+            }
+            if (type == NDIlib_frame_type_audio) {
+                const bool is_fltp = (audio_frame.FourCC == NDIlib_FourCC_audio_type_FLTP);
+                AudioInfo info;
+                if (is_fltp) {
+                    info.sample_rate    = audio_frame.sample_rate;
+                    info.channels       = audio_frame.no_channels;
+                    info.samples        = audio_frame.no_samples;
+                    info.channel_stride = audio_frame.channel_stride_in_bytes / sizeof(float);
+                }
+                NDIlib_recv_free_audio_v3(recv_, &audio_frame);
+                if (is_fltp) return info;
+            }
+        }
+        throw std::runtime_error("Timeout waiting for first audio packet");
+    }
+
     // Receives one NDI frame. On video: converts to V210 in frame_buffer/frame_stride.
     // On audio: copies float32 planar samples into audio_out and fills audio_info.
     // Returns FrameKind::None on timeout or non-A/V frames.