vf_xfade.patch

--- libavfilter/vf_xfade.c	2026-02-19 20:54:22
+++ vf_xfade.c	2026-02-19 20:54:22
@@ -126,6 +126,11 @@
     void (*transitionf)(AVFilterContext *ctx, const AVFrame *a, const AVFrame *b, AVFrame *out, float progress,
                         int slice_start, int slice_end, int jobnr);
 
+    char *easing_str; // easing name with optional args
+    char *transition_str; // transition name with optional args
+    int reverse; // reverse option bit flags (enum ReverseFlags)
+    struct XFadeEasingContext *k; // xfade-easing data
+
     AVExpr *e;
 } XFadeContext;
 
@@ -157,18 +162,22 @@
     AV_PIX_FMT_NONE
 };
 
+static void xe_data_free(struct XFadeEasingContext *k);
 static av_cold void uninit(AVFilterContext *ctx)
 {
     XFadeContext *s = ctx->priv;
 
     av_expr_free(s->e);
+    xe_data_free(s->k);
 }
 
 #define OFFSET(x) offsetof(XFadeContext, x)
 #define FLAGS (AV_OPT_FLAG_FILTERING_PARAM | AV_OPT_FLAG_VIDEO_PARAM)
 
 static const AVOption xfade_options[] = {
-    { "transition", "set cross fade transition", OFFSET(transition), AV_OPT_TYPE_INT, {.i64=FADE}, -1, NB_TRANSITIONS-1, FLAGS, .unit = "transition" },
+    { "easing", "set cross fade easing", OFFSET(easing_str), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, FLAGS },
+    { "reverse", "reverse easing/transition", OFFSET(reverse), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 3, FLAGS },
+    { "transition", "set cross fade transition", OFFSET(transition_str), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, FLAGS, .unit = "transition" },
     {   "custom",    "custom transition",     0, AV_OPT_TYPE_CONST, {.i64=CUSTOM},    0, 0, FLAGS, .unit = "transition" },
     {   "fade",      "fade transition",       0, AV_OPT_TYPE_CONST, {.i64=FADE},      0, 0, FLAGS, .unit = "transition" },
     {   "wipeleft",  "wipe left transition",  0, AV_OPT_TYPE_CONST, {.i64=WIPELEFT},  0, 0, FLAGS, .unit = "transition" },
@@ -1633,7 +1642,7 @@
         for (int y = 0; y < height; y++) {                                           \
             const float z = .5f + ((slice_start + y) / h - .5f) / progress;          \
                                                                                      \
-            if (z < 0.f || z > 1.f) {                                                \
+            if (z < 0.f || z > 1.f || isnan(z)) {                                    \
                 for (int x = 0; x < width; x++)                                      \
                     dst[x] = xf1[x];                                                 \
             } else {                                                                 \
@@ -1673,7 +1682,7 @@
             for (int x = 0; x < width; x++) {                                        \
                 const float z = .5f + (x / w - .5f) / progress;                      \
                                                                                      \
-                if (z < 0.f || z > 1.f) {                                            \
+                if (z < 0.f || z > 1.f || isnan(z)) {                                \
                     dst[x] = xf1[x];                                                 \
                 } else {                                                             \
                     const int xx = lrintf(z * (w - 1.f));                            \
@@ -2001,6 +2010,8 @@
 REVEALV_TRANSITION(down,  8, uint8_t,  1, )
 REVEALV_TRANSITION(down, 16, uint16_t, 2, )
 
+#include "xfade-easing.h" // easing & extended transitions
+
 static inline double getpix(void *priv, double x, double y, int plane, int nb)
 {
     XFadeContext *s = priv;
@@ -2102,6 +2113,9 @@
     if (s->duration)
         s->duration_pts = av_rescale_q(s->duration, AV_TIME_BASE_Q, outlink->time_base);
 
+    int ret = config_xfade_easing(ctx);
+    if (ret <= 0) return ret; // error or extended transition
+
     switch (s->transition) {
     case CUSTOM:     s->transitionf = s->depth <= 8 ? custom8_transition     : custom16_transition;     break;
     case FADE:       s->transitionf = s->depth <= 8 ? fade8_transition       : fade16_transition;       break;
@@ -2214,7 +2228,14 @@
         return AVERROR(ENOMEM);
     av_frame_copy_props(out, a);
 
-    td.xf[0] = a, td.xf[1] = b, td.out = out, td.progress = progress;
+    progress = (s->reverse & REVERSE_EASING) ? 1 - ease(s, 1 - progress) : ease(s, progress); // eased progress
+    int i = s->reverse & REVERSE_TRANSITION;
+    if (i) progress = 1 - progress;
+    if (s->reverse & REVERSE_OVERSHOOT) { // internal flag
+        if (progress < 0) progress += 1, i ^= 1; // undershoot
+        else if (progress > 1) progress -= 1, i ^= 1; // overshoot
+    }
+    td.xf[i] = a, td.xf[i ^ 1] = b, td.out = out, td.progress = av_clipf(progress, 0, 1);
     ff_filter_execute(ctx, xfade_slice, &td, NULL,
                       FFMIN(outlink->h, ff_filter_get_nb_threads(ctx)));