Smooth decode-fps stat (EMA) and enlarge SMB prefetch to 64 MiB for high-bitrate streaming

src/app/app.cpp

@@ -213,6 +213,7 @@ void App::updateStats() {
     const double fps = statsFrameAccum_ / elapsed;
     const uint64_t dec = media_.decodedFrames();
     const double decFps = static_cast<double>(dec - statsLastDecoded_) / elapsed;
+    decFpsEma_ = (decFpsEma_ > 0.0) ? decFpsEma_ * 0.6 + decFps * 0.4 : decFps;
     statsFrameAccum_ = 0;
     statsLastDecoded_ = dec;
     lastStatsUpdate_ = now;
@@ -272,7 +273,7 @@ void App::updateStats() {
         std::snprintf(buf, sizeof(buf), "Video %dx%d  %s", media_.width(),
                       media_.height(), media_.codecName().c_str());
         statsLines_.emplace_back(buf);
-        std::snprintf(buf, sizeof(buf), "Decode %.1f / %.2f fps", decFps,
+        std::snprintf(buf, sizeof(buf), "Decode %.1f / %.2f fps", decFpsEma_,
                       media_.frameRate());
         statsLines_.emplace_back(buf);
     }

src/app/app.hpp

@@ -63,6 +63,7 @@ private:
     std::chrono::steady_clock::time_point lastStatsUpdate_{};
     int statsFrameAccum_ = 0;
     uint64_t statsLastDecoded_ = 0;
+    double decFpsEma_ = 0.0;  // smoothed decode fps (the raw window is bursty)
     unsigned long long cpuPrevIdle_ = 0;
     unsigned long long cpuPrevTotal_ = 0;
     std::vector<std::string> statsLines_;

src/media/media_engine.cpp

@@ -60,7 +60,7 @@ void smb_auth(SMBCCTX*, const char*, const char*, char*, int, char* un, int unle
 // Only the prefetch thread touches the SMB handle (read/lseek); the AVIO
 // callbacks only touch the ring and request seeks.
 struct SmbReadAhead {
-    static constexpr std::size_t kCapacity = 32u << 20;  // 32 MiB cushion
+    static constexpr std::size_t kCapacity = 64u << 20;  // 64 MiB cushion
     static constexpr std::size_t kChunk = 256u << 10;    // 256 KiB network reads
 
     SMBCCTX* ctx = nullptr;