fix decklink-out: init grains_read from current time to avoid epoch realignment

nodes/decklink-out/src/decklink_out_node.cpp

@@ -226,6 +226,13 @@ void DeckLinkOutNode::process() {
         return;
     }
 
+    if (first_frame_) {
+        auto now = mxlGetTime();
+        grains_read_ = mxlTimestampToIndex(&output_rate_, now);
+        first_frame_ = false;
+        spdlog::info("DeckLink-out: starting at output index {}", grains_read_);
+    }
+
     auto deadline = mxlIndexToTimestamp(&output_rate_, grains_read_ + 1);
     mxlSleepUntil(deadline);