@@ -10422,6 +10422,24 @@ Specify the color of the padded area. For the syntax of this option,

 check the "Color" section in the ffmpeg-utils manual.

 The default value of @var{color} is "black".

+

+@item eval

+Specify when to evaluate  @var{width}, @var{height}, @var{x} and @var{y} expression.

+

+It accepts the following values:

+

+@table @samp

+@item init

+Only evaluate expressions once during the filter initialization or when

+a command is processed.

+

+@item frame

+Evaluate expressions for each incoming frame.

+

+@end table

+

+Default value is @samp{init}.

+

 @end table

 The value for the @var{width}, @var{height}, @var{x}, and @var{y}

@@ -75,11 +75,18 @@ static int query_formats(AVFilterContext *ctx)

     return ff_set_common_formats(ctx, ff_draw_supported_pixel_formats(0));

 }

+enum EvalMode {

+    EVAL_MODE_INIT,

+    EVAL_MODE_FRAME,

+    EVAL_MODE_NB

+};

+

 typedef struct PadContext {

     const AVClass *class;

     int w, h;               ///< output dimensions, a value of 0 will result in the input size

     int x, y;               ///< offsets of the input area with respect to the padded area

     int in_w, in_h;         ///< width and height for the padded input video, which has to be aligned to the chroma values in order to avoid chroma issues

+    int inlink_w, inlink_h;

     char *w_expr;           ///< width  expression string

     char *h_expr;           ///< height expression string

@@ -88,6 +95,8 @@ typedef struct PadContext {

     uint8_t rgba_color[4];  ///< color for the padding area

     FFDrawContext draw;

     FFDrawColor color;

+

+    int eval_mode;          ///< expression evaluation mode

 } PadContext;

 static int config_input(AVFilterLink *inlink)

@@ -163,6 +172,8 @@ static int config_input(AVFilterLink *inlink)

     s->y    = ff_draw_round_to_sub(&s->draw, 1, -1, s->y);

     s->in_w = ff_draw_round_to_sub(&s->draw, 0, -1, inlink->w);

     s->in_h = ff_draw_round_to_sub(&s->draw, 1, -1, inlink->h);

+    s->inlink_w = inlink->w;

+    s->inlink_h = inlink->h;

     av_log(ctx, AV_LOG_VERBOSE, "w:%d h:%d -> w:%d h:%d x:%d y:%d color:0x%02X%02X%02X%02X\n",

            inlink->w, inlink->h, s->w, s->h, s->x, s->y,

@@ -290,8 +301,35 @@ static int frame_needs_copy(PadContext *s, AVFrame *frame)

 static int filter_frame(AVFilterLink *inlink, AVFrame *in)

 {

     PadContext *s = inlink->dst->priv;

+    AVFilterLink *outlink = inlink->dst->outputs[0];

     AVFrame *out;

-    int needs_copy = frame_needs_copy(s, in);

+    int needs_copy;

+    if(s->eval_mode == EVAL_MODE_FRAME && (

+           in->width  != s->inlink_w

+        || in->height != s->inlink_h

+        || in->format != outlink->format

+        || in->sample_aspect_ratio.den != outlink->sample_aspect_ratio.den || in->sample_aspect_ratio.num != outlink->sample_aspect_ratio.num)) {

+        int ret;

+

+        inlink->dst->inputs[0]->format = in->format;

+        inlink->dst->inputs[0]->w      = in->width;

+        inlink->dst->inputs[0]->h      = in->height;

+

+        inlink->dst->inputs[0]->sample_aspect_ratio.den = in->sample_aspect_ratio.den;

+        inlink->dst->inputs[0]->sample_aspect_ratio.num = in->sample_aspect_ratio.num;

+

+

+        if ((ret = config_input(inlink)) < 0) {

+            s->inlink_w = -1;

+            return ret;

+        }

+        if ((ret = config_output(outlink)) < 0) {

+            s->inlink_w = -1;

+            return ret;

+        }

+    }

+

+    needs_copy = frame_needs_copy(s, in);

     if (needs_copy) {

         av_log(inlink->dst, AV_LOG_DEBUG, "Direct padding impossible allocating new frame\n");

@@ -364,6 +402,9 @@ static const AVOption pad_options[] = {

     { "x",      "set the x offset expression for the input image position", OFFSET(x_expr), AV_OPT_TYPE_STRING, {.str = "0"}, CHAR_MIN, CHAR_MAX, FLAGS },

     { "y",      "set the y offset expression for the input image position", OFFSET(y_expr), AV_OPT_TYPE_STRING, {.str = "0"}, CHAR_MIN, CHAR_MAX, FLAGS },

     { "color",  "set the color of the padded area border", OFFSET(rgba_color), AV_OPT_TYPE_COLOR, {.str = "black"}, .flags = FLAGS },

+    { "eval",   "specify when to evaluate expressions",    OFFSET(eval_mode), AV_OPT_TYPE_INT, {.i64 = EVAL_MODE_INIT}, 0, EVAL_MODE_NB-1, FLAGS, "eval" },

+         { "init",  "eval expressions once during initialization", 0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_INIT},  .flags = FLAGS, .unit = "eval" },

+         { "frame", "eval expressions during initialization and per-frame", 0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_FRAME}, .flags = FLAGS, .unit = "eval" },

     { NULL }

 };