@@ -505,6 +505,32 @@ If both text and textfile are specified, an error is thrown.

 @item x, y

 The offsets where text will be drawn within the video frame.

 Relative to the top/left border of the output image.

+They accept expressions similar to the @ref{overlay} filter:

+@table @option

+

+@item x, y

+the computed values for @var{x} and @var{y}. They are evaluated for

+each new frame.

+

+@item main_w, main_h

+main input width and height

+

+@item W, H

+same as @var{main_w} and @var{main_h}

+

+@item text_w, text_h

+rendered text width and height

+

+@item w, h

+same as @var{text_w} and @var{text_h}

+

+@item n

+the number of frames processed, starting from 0

+

+@item t

+timestamp expressed in seconds, NAN if the input timestamp is unknown

+

+@end table

 The default value of @var{x} and @var{y} is 0.

@@ -1048,6 +1074,7 @@ other parameters is 0.

 These parameters correspond to the parameters assigned to the

 libopencv function @code{cvSmooth}.

+@anchor{overlay}

 @section overlay

 Overlay one video on top of another.

@@ -31,7 +31,9 @@

 #include "libavutil/colorspace.h"

 #include "libavutil/file.h"

+#include "libavutil/eval.h"

 #include "libavutil/opt.h"

+#include "libavutil/mathematics.h"

 #include "libavutil/parseutils.h"

 #include "libavutil/pixdesc.h"

 #include "libavutil/tree.h"

@@ -45,6 +47,36 @@

 #include FT_FREETYPE_H

 #include FT_GLYPH_H

+static const char *var_names[] = {

+    "E",

+    "PHI",

+    "PI",

+    "main_w",    "W", ///< width  of the main    video

+    "main_h",    "H", ///< height of the main    video

+    "text_w",    "w", ///< width  of the overlay text

+    "text_h",    "h", ///< height of the overlay text

+    "x",

+    "y",

+    "n",              ///< number of processed frames

+    "t",              ///< timestamp expressed in seconds

+    NULL

+};

+

+enum var_name {

+    VAR_E,

+    VAR_PHI,

+    VAR_PI,

+    VAR_MAIN_W, VAR_MW,

+    VAR_MAIN_H, VAR_MH,

+    VAR_TEXT_W, VAR_TW,

+    VAR_TEXT_H, VAR_TH,

+    VAR_X,

+    VAR_Y,

+    VAR_N,

+    VAR_T,

+    VAR_VARS_NB

+};

+

 typedef struct {

     const AVClass *class;

     uint8_t *fontfile;              ///< font to be used

@@ -81,6 +113,10 @@ typedef struct {

     int pixel_step[4];              ///< distance in bytes between the component of each pixel

     uint8_t rgba_map[4];            ///< map RGBA offsets to the positions in the packed RGBA format

     uint8_t *box_line[4];           ///< line used for filling the box background

+    char   *x_expr, *y_expr;

+    AVExpr *x_pexpr, *y_pexpr;      ///< parsed expressions for x and y

+    double var_values[VAR_VARS_NB];

+    int draw;                       ///< set to zero to prevent drawing

 } DrawTextContext;

 #define OFFSET(x) offsetof(DrawTextContext, x)

@@ -94,8 +130,8 @@ static const AVOption drawtext_options[]= {

 {"shadowcolor", "set shadow color",  OFFSET(shadowcolor_string), AV_OPT_TYPE_STRING, {.str=NULL},  CHAR_MIN, CHAR_MAX },

 {"box",      "set box",              OFFSET(draw_box),           AV_OPT_TYPE_INT,    {.dbl=0},     0,        1        },

 {"fontsize", "set font size",        OFFSET(fontsize),           AV_OPT_TYPE_INT,    {.dbl=16},    1,        72       },

-{"x",        "set x",                OFFSET(x),                  AV_OPT_TYPE_INT,    {.dbl=0},     0,        INT_MAX  },

-{"y",        "set y",                OFFSET(y),                  AV_OPT_TYPE_INT,    {.dbl=0},     0,        INT_MAX  },

+{"x",        "set x",                OFFSET(x_expr),             AV_OPT_TYPE_STRING, {.str="0"},   CHAR_MIN, CHAR_MAX },

+{"y",        "set y",                OFFSET(y_expr),             AV_OPT_TYPE_STRING, {.str="0"},   CHAR_MIN, CHAR_MAX },

 {"shadowx",  "set x",                OFFSET(shadowx),            AV_OPT_TYPE_INT,    {.dbl=0},     INT_MIN,  INT_MAX  },

 {"shadowy",  "set y",                OFFSET(shadowy),            AV_OPT_TYPE_INT,    {.dbl=0},     INT_MIN,  INT_MAX  },

 {"tabsize",  "set tab size",         OFFSET(tabsize),            AV_OPT_TYPE_INT,    {.dbl=4},     0,        INT_MAX  },

@@ -374,7 +410,7 @@ static inline int is_newline(uint32_t c)

     return (c == '\n' || c == '\r' || c == '\f' || c == '\v');

 }

-static int dtext_prepare_text(AVFilterContext *ctx, int width, int height)

+static int dtext_prepare_text(AVFilterContext *ctx)

 {

     DrawTextContext *dtext = ctx->priv;

     uint32_t code = 0, prev_code = 0;

@@ -387,6 +423,8 @@ static int dtext_prepare_text(AVFilterContext *ctx, int width, int height)

     FT_Vector delta;

     Glyph *glyph = NULL, *prev_glyph = NULL;

     Glyph dummy = { 0 };

+    int width  = ctx->inputs[0]->w;

+    int height = ctx->inputs[0]->h;

 #if HAVE_LOCALTIME_R

     time_t now = time(0);

@@ -504,6 +542,27 @@ static int config_input(AVFilterLink *inlink)

     dtext->hsub = pix_desc->log2_chroma_w;

     dtext->vsub = pix_desc->log2_chroma_h;

+    dtext->var_values[VAR_E  ] = M_E;

+    dtext->var_values[VAR_PHI] = M_PHI;

+    dtext->var_values[VAR_PI ] = M_PI;

+

+    dtext->var_values[VAR_MAIN_W] =

+        dtext->var_values[VAR_MW] = ctx->inputs[0]->w;

+    dtext->var_values[VAR_MAIN_H] =

+        dtext->var_values[VAR_MH] = ctx->inputs[0]->h;

+

+    dtext->var_values[VAR_X] = 0;

+    dtext->var_values[VAR_Y] = 0;

+    dtext->var_values[VAR_N] = 0;

+    dtext->var_values[VAR_T] = NAN;

+

+

+    if ((ret = av_expr_parse(&dtext->x_pexpr, dtext->x_expr, var_names,

+                             NULL, NULL, NULL, NULL, 0, ctx)) < 0 ||

+        (ret = av_expr_parse(&dtext->y_pexpr, dtext->y_expr, var_names,

+                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)

+        return AVERROR(EINVAL);

+

     if ((ret =

          ff_fill_line_with_color(dtext->box_line, dtext->pixel_step,

                                  inlink->w, dtext->boxcolor,

@@ -524,7 +583,9 @@ static int config_input(AVFilterLink *inlink)

         dtext->shadowcolor[3] = rgba[3];

     }

-    return dtext_prepare_text(ctx, ctx->inputs[0]->w, ctx->inputs[0]->h);

+    dtext->draw = 1;

+

+    return dtext_prepare_text(ctx);

 }

 #define GET_BITMAP_VAL(r, c)                                            \

@@ -697,15 +758,71 @@ static int draw_text(AVFilterContext *ctx, AVFilterBufferRef *picref,

 static void null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir) { }

+static inline int normalize_double(int *n, double d)

+{

+    int ret = 0;

+

+    if (isnan(d)) {

+        ret = AVERROR(EINVAL);

+    } else if (d > INT_MAX || d < INT_MIN) {

+        *n = d > INT_MAX ? INT_MAX : INT_MIN;

+        ret = AVERROR(EINVAL);

+    } else

+        *n = round(d);

+

+    return ret;

+}

+

+static void start_frame(AVFilterLink *inlink, AVFilterBufferRef *inpicref)

+{

+    AVFilterContext *ctx = inlink->dst;

+    DrawTextContext *dtext = ctx->priv;

+

+    if (dtext_prepare_text(ctx) < 0) {

+        av_log(ctx, AV_LOG_ERROR, "Can't draw text\n");

+        dtext->draw = 0;

+    }

+

+    dtext->var_values[VAR_T] = inpicref->pts == AV_NOPTS_VALUE ?

+        NAN : inpicref->pts * av_q2d(inlink->time_base);

+    dtext->var_values[VAR_X] =

+        av_expr_eval(dtext->x_pexpr, dtext->var_values, NULL);

+    dtext->var_values[VAR_Y] =

+        av_expr_eval(dtext->y_pexpr, dtext->var_values, NULL);

+    dtext->var_values[VAR_X] =

+        av_expr_eval(dtext->x_pexpr, dtext->var_values, NULL);

+

+    normalize_double(&dtext->x, dtext->var_values[VAR_X]);

+    normalize_double(&dtext->y, dtext->var_values[VAR_Y]);

+

+    if (dtext->x < 0) dtext->x = 0;

+    if (dtext->y < 0) dtext->y = 0;

+    if ((unsigned)dtext->x + (unsigned)dtext->w > inlink->w)

+        dtext->x = inlink->w - dtext->w;

+    if ((unsigned)dtext->y + (unsigned)dtext->h > inlink->h)

+        dtext->y = inlink->h - dtext->h;

+

+    dtext->x &= ~((1 << dtext->hsub) - 1);

+    dtext->y &= ~((1 << dtext->vsub) - 1);

+

+    av_dlog(ctx, "n:%d t:%f x:%d y:%d x+w:%d y+h:%d\n",

+            (int)dtext->var_values[VAR_N], dtext->var_values[VAR_T],

+            dtext->x, dtext->y, dtext->x+dtext->w, dtext->y+dtext->h);

+

+    avfilter_start_frame(inlink->dst->outputs[0], inpicref);

+}

+

 static void end_frame(AVFilterLink *inlink)

 {

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

     AVFilterBufferRef *picref = inlink->cur_buf;

-    int err = dtext_prepare_text(inlink->dst,

-                                 picref->video->w, picref->video->h);

-    if (!err)

+    DrawTextContext *dtext = inlink->dst->priv;

+

+    if (dtext->draw)

         draw_text(inlink->dst, picref, picref->video->w, picref->video->h);

+    dtext->var_values[VAR_N] += 1.0;

+

     avfilter_draw_slice(outlink, 0, picref->video->h, 1);

     avfilter_end_frame(outlink);

 }

@@ -721,7 +838,7 @@ AVFilter avfilter_vf_drawtext = {

     .inputs    = (AVFilterPad[]) {{ .name             = "default",

                                     .type             = AVMEDIA_TYPE_VIDEO,

                                     .get_video_buffer = avfilter_null_get_video_buffer,

-                                    .start_frame      = avfilter_null_start_frame,

+                                    .start_frame      = start_frame,

                                     .draw_slice       = null_draw_slice,

                                     .end_frame        = end_frame,

                                     .config_props     = config_input,