Merge pull request #552 from webadderallorg/fix/windows-wgc-relative-timestamps

fix(windows): normalize WGC video timestamps

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

@@ -5,10 +5,10 @@
 	"helpers": {
 		"wgc-capture": {
 			"binaryName": "wgc-capture.exe",
-			"binarySha256": "b840fb2847ac8fcfc5137febfc8dd49b55a4d15bea4f9185a0916fb0c1544bed",
+			"binarySha256": "47a67765a0b7fdd9936e41a2f7e62f6408bd426774f7854e6378194ebe3ae827",
 			"sourceDir": "electron/native/wgc-capture",
-			"sourceFingerprint": "fdbc8002a894a1300c7fed58a0f7aae18119dbb2bd71bcaacf3bfc398db904a9",
-			"updatedAt": "2026-05-22T10:12:36.734Z"
+			"sourceFingerprint": "696c9f56da75105941063b7940eb91c231e781e9a3a4ba885e47bcfdf798f13f",
+			"updatedAt": "2026-05-22T10:43:18.337Z"
 		},
 		"cursor-monitor": {
 			"binaryName": "cursor-monitor.exe",

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

@@ -152,6 +152,7 @@ bool MFEncoder::initialize(const std::wstring& outputPath, int width, int height
     const int uvSize = (width_ / 2) * (height_ / 2) * 2;
     nv12Buffer_.resize(ySize + uvSize);
     lastFrameBuffer_.clear();
+    firstSampleTimeHns_ = -1;
     lastSampleTimeHns_ = -1;
 
     initialized_ = true;
@@ -234,14 +235,17 @@ bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
 
     // 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)) {
+    int64_t normalizedTimestampHns = 0;
+    normalizeWriteTimestampHnsLocked(timestampHns, normalizedTimestampHns);
+
+    if (!lastFrameBuffer_.empty() && !extendLastFrameToLocked(normalizedTimestampHns)) {
         return false;
     }
 
-    bool wroteSample = writeNv12SampleLocked(nv12Buffer_, timestampHns);
+    bool wroteSample = writeNv12SampleLocked(nv12Buffer_, normalizedTimestampHns);
     if (wroteSample) {
         lastFrameBuffer_ = nv12Buffer_;
-        lastSampleTimeHns_ = timestampHns;
+        lastSampleTimeHns_ = normalizedTimestampHns;
     }
     return wroteSample;
 }
@@ -249,7 +253,36 @@ bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
 bool MFEncoder::extendLastFrameTo(int64_t timestampHns) {
     std::lock_guard<std::mutex> lock(mutex_);
 
-    return extendLastFrameToLocked(timestampHns);
+    int64_t normalizedTimestampHns = 0;
+    if (!normalizeTimelineTimestampHnsLocked(timestampHns, normalizedTimestampHns)) {
+        return false;
+    }
+
+    return extendLastFrameToLocked(normalizedTimestampHns);
+}
+
+void MFEncoder::normalizeWriteTimestampHnsLocked(int64_t timestampHns, int64_t& normalizedTimestampHns) {
+    if (firstSampleTimeHns_ < 0) {
+        firstSampleTimeHns_ = timestampHns < 0 ? 0 : timestampHns;
+    }
+
+    normalizedTimestampHns = timestampHns - firstSampleTimeHns_;
+    if (normalizedTimestampHns < 0) {
+        normalizedTimestampHns = 0;
+    }
+}
+
+bool MFEncoder::normalizeTimelineTimestampHnsLocked(
+    int64_t timestampHns,
+    int64_t& normalizedTimestampHns
+) const {
+    if (firstSampleTimeHns_ < 0) return false;
+
+    normalizedTimestampHns = timestampHns - firstSampleTimeHns_;
+    if (normalizedTimestampHns < 0) {
+        normalizedTimestampHns = 0;
+    }
+    return true;
 }
 
 bool MFEncoder::extendLastFrameToLocked(int64_t timestampHns) {
@@ -332,6 +365,7 @@ bool MFEncoder::finalize() {
     lastFrameBuffer_.clear();
     nv12Buffer_.shrink_to_fit();
     lastFrameBuffer_.shrink_to_fit();
+    firstSampleTimeHns_ = -1;
     lastSampleTimeHns_ = -1;
     MFShutdown();
     return SUCCEEDED(hr);

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

@@ -24,6 +24,8 @@ public:
     bool finalize();
 
 private:
+    void normalizeWriteTimestampHnsLocked(int64_t timestampHns, int64_t& normalizedTimestampHns);
+    bool normalizeTimelineTimestampHnsLocked(int64_t timestampHns, int64_t& normalizedTimestampHns) const;
     bool extendLastFrameToLocked(int64_t timestampHns);
     bool writeNv12SampleLocked(const std::vector<uint8_t>& frameBuffer, int64_t timestampHns);
 
@@ -39,6 +41,7 @@ private:
     int width_ = 0;
     int height_ = 0;
     int fps_ = 60;
+    int64_t firstSampleTimeHns_ = -1;
     int64_t lastSampleTimeHns_ = -1;
     bool initialized_ = false;
     std::mutex mutex_;