fix(windows): preserve WGC duration through static frames

electron/native/bin/win32-x64/helpers-manifest.json

@@ -5,10 +5,10 @@
   "helpers": {
     "wgc-capture": {
       "binaryName": "wgc-capture.exe",
-      "binarySha256": "4f8873abbff58add37672114184c154dee838939ee8f2b7df45d658d078af28c",
+      "binarySha256": "a04ecf49a5c0b9b92dfb9cd3aa1468178f7a144ac8b78b433e99b34425e35eac",
       "sourceDir": "electron/native/wgc-capture",
-      "sourceFingerprint": "6f725fad6eb515d81b2d553ec45ddbf7c681d2725bba48f0c0722ce00166d967",
-      "updatedAt": "2026-05-09T00:49:28.306Z"
+      "sourceFingerprint": "ef3602f1641538a9a19def9da84f1fcd8e37eb53f3e55c1ddf46f26ba75eb54c",
+      "updatedAt": "2026-05-22T08:56:01.149Z"
     },
     "cursor-monitor": {
       "binaryName": "cursor-monitor.exe",

electron/native/wgc-capture/src/mf_encoder.cpp

@@ -227,6 +227,12 @@ bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
 
     context_->Unmap(stagingTexture_.Get(), 0);
 
+    // WGC may stop delivering frames while the scene is static; keep the MP4
+    // timeline continuous by repeating the previous frame before writing a new one.
+    if (!lastFrameBuffer_.empty() && !extendLastFrameToLocked(timestampHns)) {
+        return false;
+    }
+
     bool wroteSample = writeNv12SampleLocked(nv12Buffer_, timestampHns);
     if (wroteSample) {
         lastFrameBuffer_ = nv12Buffer_;
@@ -238,19 +244,29 @@ bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
 bool MFEncoder::extendLastFrameTo(int64_t timestampHns) {
     std::lock_guard<std::mutex> lock(mutex_);
 
+    return extendLastFrameToLocked(timestampHns);
+}
+
+bool MFEncoder::extendLastFrameToLocked(int64_t timestampHns) {
     if (!initialized_ || !sinkWriter_) return false;
     if (lastFrameBuffer_.empty()) return false;
+    if (lastSampleTimeHns_ < 0) return false;
 
     const int64_t frameDurationHns = 10000000LL / fps_;
-    if (lastSampleTimeHns_ >= 0 && timestampHns <= lastSampleTimeHns_ + frameDurationHns) {
+    if (frameDurationHns <= 0) return false;
+    if (timestampHns <= lastSampleTimeHns_ + frameDurationHns) {
         return true;
     }
 
-    if (!writeNv12SampleLocked(lastFrameBuffer_, timestampHns)) {
-        return false;
+    int64_t nextSampleTimeHns = lastSampleTimeHns_ + frameDurationHns;
+    while (nextSampleTimeHns + frameDurationHns <= timestampHns) {
+        if (!writeNv12SampleLocked(lastFrameBuffer_, nextSampleTimeHns)) {
+            return false;
+        }
+        lastSampleTimeHns_ = nextSampleTimeHns;
+        nextSampleTimeHns += frameDurationHns;
     }
 
-    lastSampleTimeHns_ = timestampHns;
     return true;
 }
 

electron/native/wgc-capture/src/mf_encoder.h

@@ -24,6 +24,7 @@ public:
     bool finalize();
 
 private:
+    bool extendLastFrameToLocked(int64_t timestampHns);
     bool writeNv12SampleLocked(const std::vector<uint8_t>& frameBuffer, int64_t timestampHns);
 
     ComPtr<IMFSinkWriter> sinkWriter_;