From c451fe3fe1656d7343413210d56306279486f85f Mon Sep 17 00:00:00 2001
From: Crend King <975235+CrendKing@users.noreply.github.com>
Date: Mon, 21 Dec 2020 23:49:38 -0800
Subject: [PATCH] Fix bug that skips the first source frame when creating
 output frames

---
 avisynth_filter/src/frame_handler.cpp | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/avisynth_filter/src/frame_handler.cpp b/avisynth_filter/src/frame_handler.cpp
index c8abba6..e9f5016 100644
--- a/avisynth_filter/src/frame_handler.cpp
+++ b/avisynth_filter/src/frame_handler.cpp
@@ -58,9 +58,15 @@ auto FrameHandler::AddInputSample(IMediaSample *inSample) -> HRESULT {
         return VFW_E_SAMPLE_REJECTED;
     }
 
-    if (_nextOutputFrameStartTime == 0) {
+    if (_nextOutputFrameStartTime == -1) {
         _nextOutputFrameStartTime = srcFrameInfo.startTime;
     }
+    if (_frameRateCheckpointInputSampleStartTime == -1) {
+        _frameRateCheckpointInputSampleStartTime = srcFrameInfo.startTime;
+    }
+    if (_frameRateCheckpointOutputFrameStartTime == -1) {
+        _frameRateCheckpointOutputFrameStartTime = srcFrameInfo.startTime;
+    }
 
     RefreshInputFrameRates(srcFrameInfo);
 
@@ -294,12 +300,12 @@ auto FrameHandler::Reset() -> void {
     _nextSourceFrameNb = 0;
     _nextOutputFrameNb = 0;
     _nextDeliverFrameNb = 0;
-    _nextOutputFrameStartTime = 0;
+    _nextOutputFrameStartTime = -1;
 
     _frameRateCheckpointInputSampleNb = 0;
-    _frameRateCheckpointInputSampleStartTime = 0;
+    _frameRateCheckpointInputSampleStartTime = -1;
     _frameRateCheckpointOutputFrameNb = 0;
-    _frameRateCheckpointOutputFrameStartTime = 0;
+    _frameRateCheckpointOutputFrameStartTime = -1;
     _currentInputFrameRate = 0;
     _currentOutputFrameRate = 0;
 }
@@ -414,6 +420,8 @@ auto FrameHandler::GarbageCollect(int srcFrameNb) -> void {
 
     const size_t dbgPreSize = _sourceFrames.size();
 
+    // search for all previous zero-ref frames in case of some source frames are never used
+    // this could happen by plugins that decrease frame rate
     auto iter = _sourceFrames.begin();
     do {
         if (iter->first == srcFrameNb) {