Add stream API merge utils.

PiperOrigin-RevId: 571124981

mediapipe/framework/api2/stream/BUILD

@@ -237,6 +237,28 @@ cc_test(
     ],
 )
 
+cc_library(
+    name = "merge",
+    hdrs = ["merge.h"],
+    deps = [
+        "//mediapipe/calculators/core:merge_calculator",
+        "//mediapipe/framework/api2:builder",
+    ],
+)
+
+cc_test(
+    name = "merge_test",
+    srcs = ["merge_test.cc"],
+    deps = [
+        ":merge",
+        "//mediapipe/framework:calculator_framework",
+        "//mediapipe/framework/api2:builder",
+        "//mediapipe/framework/port:gtest",
+        "//mediapipe/framework/port:gtest_main",
+        "//mediapipe/framework/port:parse_text_proto",
+    ],
+)
+
 cc_library(
     name = "presence",
     hdrs = ["presence.h"],

mediapipe/framework/api2/stream/merge.h

@@ -0,0 +1,20 @@
+#ifndef MEDIAPIPE_FRAMEWORK_API2_STREAM_MERGE_H_
+#define MEDIAPIPE_FRAMEWORK_API2_STREAM_MERGE_H_
+
+#include "mediapipe/framework/api2/builder.h"
+
+namespace mediapipe::api2::builder {
+
+// Updates @graph to choose @a stream if it's available (not empty stream at
+// specific timestamp) or @b stream otherwise.
+template <typename T>
+Stream<T> Merge(Stream<T> a, Stream<T> b, Graph& graph) {
+  auto& merge_node = graph.AddNode("MergeCalculator");
+  a.ConnectTo(merge_node.In("")[0]);
+  b.ConnectTo(merge_node.In("")[1]);
+  return merge_node.Out("").template Cast<T>();
+}
+
+}  // namespace mediapipe::api2::builder
+
+#endif  // MEDIAPIPE_FRAMEWORK_API2_STREAM_MERGE_H_

mediapipe/framework/api2/stream/merge_test.cc

@@ -0,0 +1,35 @@
+#include "mediapipe/framework/api2/stream/merge.h"
+
+#include "mediapipe/framework/api2/builder.h"
+#include "mediapipe/framework/calculator_framework.h"
+#include "mediapipe/framework/port/gmock.h"
+#include "mediapipe/framework/port/gtest.h"
+#include "mediapipe/framework/port/parse_text_proto.h"
+
+namespace mediapipe::api2::builder {
+namespace {
+
+TEST(Merge, VerifyConfig) {
+  mediapipe::api2::builder::Graph graph;
+
+  Stream<int> input_a = graph.In("INPUT_A").Cast<int>();
+  Stream<int> input_b = graph.In("INPUT_B").Cast<int>();
+  Stream<int> input = Merge(input_a, input_b, graph);
+  input.SetName("input");
+
+  EXPECT_THAT(
+      graph.GetConfig(),
+      EqualsProto(mediapipe::ParseTextProtoOrDie<CalculatorGraphConfig>(R"pb(
+        node {
+          calculator: "MergeCalculator"
+          input_stream: "__stream_0"
+          input_stream: "__stream_1"
+          output_stream: "input"
+        }
+        input_stream: "INPUT_A:__stream_0"
+        input_stream: "INPUT_B:__stream_1"
+      )pb")));
+}
+
+}  // namespace
+}  // namespace mediapipe::api2::builder