vf_xfade.patch

--- libavfilter/vf_xfade.c	2025-02-21 00:54:54.000000000 +0000
+++ vf_xfade.c	2025-02-21 00:54:54.000000000 +0000
@@ -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 ReverseOpts)
+    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" },
@@ -2001,10 +2010,12 @@
 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;
-    AVFrame *in = s->xf[nb];
+    AVFrame *in = s->xf[nb ^ (s->reverse & REVERSE_TRANSITION)];
     const uint8_t *src = in->data[FFMIN(plane, s->nb_planes - 1)];
     int linesize = in->linesize[FFMIN(plane, s->nb_planes - 1)];
     const int w = in->width;
@@ -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;
@@ -2195,8 +2209,12 @@
     ThreadData *td = arg;
     int slice_start = (outlink->h *  jobnr   ) / nb_jobs;
     int slice_end   = (outlink->h * (jobnr+1)) / nb_jobs;
+    int i = s->reverse & REVERSE_TRANSITION; // input 0 or 1
+    float p = td->progress;
 
-    s->transitionf(ctx, td->xf[0], td->xf[1], td->out, td->progress, slice_start, slice_end, jobnr);
+    p = (s->reverse & REVERSE_EASING) ? 1 - ease(s, 1 - p) : ease(s, p); // eased progress
+    if (i) p = 1 - p;
+    s->transitionf(ctx, td->xf[i], td->xf[i ^ 1], td->out, p, slice_start, slice_end, jobnr);
 
     return 0;
 }