Use PTS differences for _Duration props

frame->duration is often just computed from the track-wide frame rate and hence unreliable. For the last frame, where no following PTS is available, the logic just matches the previous frames's duration. In theory the track's duration could be referenced instead, but the current logic matches FFMS2.
vapoursynth · Feb 9, 2025 · 546ea79 · 546ea79
1 parent eef4d1d
commit 546ea79
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Showing 4 changed files with 16 additions and 8 deletions.
diff --git a/src/avisynth.cpp b/src/avisynth.cpp
@@ -255,10 +255,9 @@ class AvisynthVideoSource : public IClip {
             Env->ThrowError("BestVideoSource: %s", e.what());
         }
 
-        const BSVideoProperties &VP = V->GetVideoProperties();
         AVSMap *Props = Env->getFramePropsRW(Dst);
 
-        SetSynthFrameProperties(Src, VP, RFF, V->GetFrameIsTFF(n, RFF),
+        SetSynthFrameProperties(n, Src, *V, RFF, V->GetFrameIsTFF(n, RFF),
             [Props, Env](const char *Name, int64_t V) { Env->propSetInt(Props, Name, V, 1); },
             [Props, Env](const char *Name, double V) { Env->propSetFloat(Props, Name, V, 1); },
             [Props, Env](const char *Name, const char *V, int Size, bool Utf8) { Env->propSetData(Props, Name, V, Size, 1); });

diff --git a/src/synthshared.cpp b/src/synthshared.cpp
@@ -21,7 +21,9 @@
 #include "synthshared.h"
 #include "VSHelper4.h"
 
-void SetSynthFrameProperties(const std::unique_ptr<BestVideoFrame> &Src, const BSVideoProperties &VP, bool RFF, bool TFF, const std::function<void(const char *, int64_t)> &mapSetInt, const std::function<void(const char *, double)> &mapSetFloat, const std::function<void(const char *, const char *, int, bool)> &mapSetData) {
+void SetSynthFrameProperties(int n, const std::unique_ptr<BestVideoFrame> &Src, const BestVideoSource &VS, bool RFF, bool TFF, const std::function<void(const char *, int64_t)> &mapSetInt, const std::function<void(const char *, double)> &mapSetFloat, const std::function<void(const char *, const char *, int, bool)> &mapSetData) {
+    const BSVideoProperties VP = VS.GetVideoProperties();
+
     // Set AR variables
     if (VP.SAR.Num > 0 && VP.SAR.Den > 0) {
         mapSetInt("_SARNum", VP.SAR.Num);
@@ -49,11 +51,19 @@ void SetSynthFrameProperties(const std::unique_ptr<BestVideoFrame> &Src, const B
         mapSetInt("_FieldBased", FieldBased);
         mapSetInt("RepeatField", Src->RepeatPict);
 
-        // FIXME, use PTS difference between frames instead?
         if (Src->Duration > 0) {
             int64_t DurNum = VP.TimeBase.Num;
             int64_t DurDen = VP.TimeBase.Den;
-            vsh::muldivRational(&DurNum, &DurDen, Src->Duration, 1);
+
+            int64_t Dur = Src->Duration;
+            if (n < VP.NumFrames - 1) {
+                Dur = VS.GetFrameInfo(n + 1).PTS - Src->PTS;
+            } else if (VP.NumFrames >= 2) {
+                // Assume the last frame has the same duration as the previous one, if the latter exists
+                Dur = Src->PTS - VS.GetFrameInfo(n - 1).PTS;
+            }
+
+            vsh::muldivRational(&DurNum, &DurDen, Dur, 1);
             mapSetInt("_DurationNum", DurNum);
             mapSetInt("_DurationDen", DurDen);
         }

diff --git a/src/synthshared.h b/src/synthshared.h
@@ -26,6 +26,6 @@
 #include <functional>
 #include <cstdint>
 
-void SetSynthFrameProperties(const std::unique_ptr<BestVideoFrame> &Src, const BSVideoProperties &VP, bool RFF, bool TFF, const std::function<void(const char *, int64_t)> &mapSetInt, const std::function<void(const char *, double)> &mapSetFloat, const std::function<void(const char *, const char *, int, bool)> &mapSetData);
+void SetSynthFrameProperties(int n, const std::unique_ptr<BestVideoFrame> &Src, const BestVideoSource &VS, bool RFF, bool TFF, const std::function<void(const char *, int64_t)> &mapSetInt, const std::function<void(const char *, double)> &mapSetFloat, const std::function<void(const char *, const char *, int, bool)> &mapSetData);
 
 #endif
diff --git a/src/vapoursynth.cpp b/src/vapoursynth.cpp
@@ -108,12 +108,11 @@ static const VSFrame *VS_CC BestVideoSourceGetFrame(int n, int ActivationReason,
             return nullptr;
         }
 
-        const BSVideoProperties &VP = D->V->GetVideoProperties();
         VSMap *Props = vsapi->getFramePropertiesRW(Dst);
         if (AlphaDst)
             vsapi->mapConsumeFrame(Props, "_Alpha", AlphaDst, maAppend);
 
-        SetSynthFrameProperties(Src, VP, D->RFF, D->V->GetFrameIsTFF(n, D->RFF),
+        SetSynthFrameProperties(n, Src, *D->V, D->RFF, D->V->GetFrameIsTFF(n, D->RFF),
             [Props, vsapi](const char *Name, int64_t V) { vsapi->mapSetInt(Props, Name, V, maAppend); },
             [Props, vsapi](const char *Name, double V) { vsapi->mapSetFloat(Props, Name, V, maAppend); },
             [Props, vsapi](const char *Name, const char *V, int Size, bool Utf8) { vsapi->mapSetData(Props, Name, V, Size, Utf8 ? dtUtf8 : dtBinary, maAppend); });