From 906c476ebe1fa518e4f82139aaee85dce63b2eb6 Mon Sep 17 00:00:00 2001
From: Pierre-Adrien Lair <pala@converteo.local>
Date: Tue, 24 Mar 2026 17:59:27 +0100
Subject: [PATCH] Fix corrupted MP4 recordings on Windows by serializing
 encoder writes

The WGC capture session uses Direct3D11CaptureFramePool::CreateFreeThreaded,
which dispatches FrameArrived callbacks on thread pool threads concurrently.
MFEncoder::writeFrame() accesses non-thread-safe resources (ID3D11DeviceContext,
IMFSinkWriter, shared staging texture and NV12 buffer) without synchronization,
causing MP4 container corruption when callbacks overlap at high frame rates.

Add a mutex to serialize writeFrame() and finalize() calls, preventing
concurrent access to the D3D context and Media Foundation sink writer.

Fixes #96
---
 electron/native/wgc-capture/src/mf_encoder.cpp | 2 ++
 electron/native/wgc-capture/src/mf_encoder.h   | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/electron/native/wgc-capture/src/mf_encoder.cpp b/electron/native/wgc-capture/src/mf_encoder.cpp
index a1474c20..1adef1b6 100644
--- a/electron/native/wgc-capture/src/mf_encoder.cpp
+++ b/electron/native/wgc-capture/src/mf_encoder.cpp
@@ -124,6 +124,7 @@ bool MFEncoder::initialize(const std::wstring& outputPath, int width, int height
 }
 
 bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
+    std::lock_guard<std::mutex> lock(writeMutex_);
     if (!initialized_ || !sinkWriter_) return false;
 
     context_->CopyResource(stagingTexture_.Get(), texture);
@@ -190,6 +191,7 @@ bool MFEncoder::writeFrame(ID3D11Texture2D* texture, int64_t timestampHns) {
 }
 
 bool MFEncoder::finalize() {
+    std::lock_guard<std::mutex> lock(writeMutex_);
     if (!initialized_) return false;
     initialized_ = false;
 
diff --git a/electron/native/wgc-capture/src/mf_encoder.h b/electron/native/wgc-capture/src/mf_encoder.h
index 7eb8e642..11b9c774 100644
--- a/electron/native/wgc-capture/src/mf_encoder.h
+++ b/electron/native/wgc-capture/src/mf_encoder.h
@@ -8,6 +8,7 @@
 #include <wrl/client.h>
 #include <string>
 #include <vector>
+#include <mutex>
 
 using Microsoft::WRL::ComPtr;
 
@@ -32,4 +33,5 @@ class MFEncoder {
     int height_ = 0;
     int fps_ = 60;
     bool initialized_ = false;
+    std::mutex writeMutex_;
 };