[PATCH] Make the crop filter accept parametric expressions.

Stefano Sabatini stefano.sabatini-lala
Thu Sep 9 01:05:04 CEST 2010


---
 doc/filters.texi      |   73 ++++++++++++++++++++++-----
 libavfilter/vf_crop.c |  134 ++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 188 insertions(+), 19 deletions(-)

diff --git a/doc/filters.texi b/doc/filters.texi
index 60ecf56..48fc7d7 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -28,32 +28,79 @@ Below is a description of the currently available video filters.
 
 Crop the input video to @var{x}:@var{y}:@var{width}:@var{height}.
 
- at example
-./ffmpeg -i in.avi -vf "crop=0:0:0:240" out.avi
- at end example
+The parameters are expressions containing the following constants:
 
- at var{x} and @var{y} specify the position of the top-left corner of the
-output (non-cropped) area.
+ at table @option
+ at item E, PI, PHI
+the corresponding mathematical approximated values for e
+(euler number), pi (greek PI), PHI (golden ratio)
 
-The default value of @var{x} and @var{y} is 0.
+ at item x, y
+the computed values for @var{x} and @var{y}. They are evaluated for
+each new frame.
 
-The @var{width} and @var{height} parameters specify the width and height
-of the output (non-cropped) area.
+ at item w, h
+the input width and heigth.
 
-A value of 0 is interpreted as the maximum possible size contained in
-the area delimited by the top-left corner at position x:y.
+ at item n
+the number of input frame, starting from 0
 
-For example the parameters:
+ at item pos
+the position in the file of the input frame, NAN if unknown
+
+ at item t
+timestamp expressed in seconds
+
+ at end table
+
+ at var{x} and @var{y} specify the expressions for the position of the
+top-left corner of the output (non-cropped) area. They are evaluated
+for each frame. If the evaluated value is not valid, it is
+approximated to the nearest valid value.
+
+The default value of @var{x} and @var{y} is "0".
 
+The expression for @var{x} may depend on @var{y}, and the expression
+for @var{y} may depend on @var{x}, but you cannot have @var{x} and
+ at var{y} depend on @var{w} and @var{y}, as they are evaluated after
+ at var{x} and @var{y}.
+
+The @var{width} and @var{height} parameters specify the expressions for
+the width and height of the output (non-cropped) area. They are
+evaluated just at the configuration of the filter.
+
+The default value of @var{width} is "w-x", and the default value of
+ at var{height} is "h-y", which specify the maximum possible size
+contained in the area delimited by the top-left corner at position
+x:y.
+
+For example the parameters:
 @example
-"crop=100:100:0:0"
+"crop=100:100"
 @end example
 
 will delimit the rectangle with the top-left corner placed at position
 100:100 and the right-bottom corner corresponding to the right-bottom
 corner of the input image.
 
-The default value of @var{width} and @var{height} is 0.
+Follow other examples:
+ at example
+# crop 10 pixels from the lefth and right borders, and 20 pixels from
+# the top and bottom borders
+crop=10:20:w-2*x:h-2*y
+
+# keep only the bottom right quarter of the input image
+crop=w/2:h/2
+
+# trembling effect
+crop='10+10*sin(n/10):20+20*sin(n/5):w-2*x:h-2*y
+
+# erratic camera effect depending on timestamp
+crop='20+20*sin(3*t):10+10*sin(2*t):w-2*x:h-2*y'
+
+# set x depending on the value of y
+crop='y:10+10*sin(n/10):w-2*x:h-2*y'
+ at end example
 
 @section fifo
 
diff --git a/libavfilter/vf_crop.c b/libavfilter/vf_crop.c
index 880c954..eb5e72a 100644
--- a/libavfilter/vf_crop.c
+++ b/libavfilter/vf_crop.c
@@ -24,8 +24,38 @@
  */
 
 #include "avfilter.h"
+#include "libavutil/eval.h"
+#include "libavutil/avstring.h"
 #include "libavcore/imgutils.h"
 
+static const char *var_names[] = {
+    "E",
+    "PHI",
+    "PI",
+    "x",
+    "y",
+    "w",      ///< width  of the input video
+    "h",      ///< height of the input video
+    "n",      ///< number of frame
+    "pos",    ///< position in the file
+    "t",      ///< timestamp expressed in seconds
+    NULL
+};
+
+enum var_name {
+    E,
+    PHI,
+    PI,
+    X,
+    Y,
+    W,
+    H,
+    N,
+    POS,
+    T,
+    VARS_NB
+};
+
 typedef struct {
     int  x;             ///< x offset of the non-cropped area with respect to the input area
     int  y;             ///< y offset of the non-cropped area with respect to the input area
@@ -34,6 +64,9 @@ typedef struct {
 
     int max_step[4];    ///< max pixel step for each plane, expressed as a number of bytes
     int hsub, vsub;     ///< chroma subsampling
+    char x_expr[256], y_expr[256], w_expr[256], h_expr[256];
+    AVExpr *x_pexpr, *y_pexpr;  /* parsed expressions for x and y */
+    double var_values[VARS_NB];
 } CropContext;
 
 static int query_formats(AVFilterContext *ctx)
@@ -72,30 +105,79 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
 {
     CropContext *crop = ctx->priv;
 
+    av_strlcpy(crop->x_expr, "0"  , sizeof(crop->x_expr));
+    av_strlcpy(crop->y_expr, "0"  , sizeof(crop->y_expr));
+    av_strlcpy(crop->w_expr, "w-x", sizeof(crop->w_expr));
+    av_strlcpy(crop->h_expr, "h-y", sizeof(crop->h_expr));
+
     if (args)
-        sscanf(args, "%d:%d:%d:%d", &crop->x, &crop->y, &crop->w, &crop->h);
+        sscanf(args, "%255[^:]:%255[^:]:%255[^:]:%255[^:]", crop->x_expr, crop->y_expr, crop->w_expr, crop->h_expr);
 
     return 0;
 }
 
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    CropContext *crop = ctx->priv;
+
+    av_free_expr(crop->x_pexpr); crop->x_pexpr = NULL;
+    av_free_expr(crop->y_pexpr); crop->y_pexpr = NULL;
+}
+
 static int config_input(AVFilterLink *link)
 {
     AVFilterContext *ctx = link->dst;
     CropContext *crop = ctx->priv;
     const AVPixFmtDescriptor *pix_desc = &av_pix_fmt_descriptors[link->format];
+    int ret;
+    const char *expr;
+    double res;
+
+    crop->var_values[E  ]   = M_E;
+    crop->var_values[PHI]   = M_PHI;
+    crop->var_values[PI ]   = M_PI;
+    crop->var_values[X  ]   = NAN;
+    crop->var_values[Y  ]   = NAN;
+    crop->var_values[W  ]   = ctx->inputs[0]->w;
+    crop->var_values[H  ]   = ctx->inputs[0]->h;
+    crop->var_values[N  ]   = 0;
 
     av_image_fill_max_pixsteps(crop->max_step, NULL, pix_desc);
     crop->hsub = av_pix_fmt_descriptors[link->format].log2_chroma_w;
     crop->vsub = av_pix_fmt_descriptors[link->format].log2_chroma_h;
 
-    if (crop->w == 0)
-        crop->w = link->w - crop->x;
-    if (crop->h == 0)
-        crop->h = link->h - crop->y;
+    if ((ret = av_parse_expr(&crop->x_pexpr, crop->x_expr, var_names,
+                             NULL, NULL, NULL, NULL, 0, ctx)) < 0 ||
+        (ret = av_parse_expr(&crop->y_pexpr, crop->y_expr, var_names,
+                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
+        return AVERROR(EINVAL);
+
+    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
+    crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
+    /* evaluate again x as it may depend on y */
+    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
 
+    if (isnan(crop->var_values[X]) || isnan(crop->var_values[Y])) {
+        av_log(ctx, AV_LOG_ERROR,
+               "Invalid expression for x or y. "
+               "Maybe the expression for x:'%s' or for y:'%s' is self-referencing.\n",
+               crop->x_expr, crop->y_expr);
+        return AVERROR(EINVAL);
+    }
     crop->x &= ~((1 << crop->hsub) - 1);
     crop->y &= ~((1 << crop->vsub) - 1);
 
+    if ((ret = av_parse_and_eval_expr(&res, (expr = crop->w_expr),
+                                      var_names, crop->var_values,
+                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
+        goto fail_expr;
+    crop->w = res;
+    if ((ret = av_parse_and_eval_expr(&res, (expr = crop->h_expr),
+                                      var_names, crop->var_values,
+                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
+        goto fail_expr;
+    crop->h = res;
+
     av_log(link->dst, AV_LOG_INFO, "x:%d y:%d w:%d h:%d\n",
            crop->x, crop->y, crop->w, crop->h);
 
@@ -110,6 +192,10 @@ static int config_input(AVFilterLink *link)
     }
 
     return 0;
+
+fail_expr:
+    av_log(NULL, AV_LOG_ERROR, "Error when evaluating the expression '%s'\n", expr);
+    return ret;
 }
 
 static int config_output(AVFilterLink *link)
@@ -124,13 +210,39 @@ static int config_output(AVFilterLink *link)
 
 static void start_frame(AVFilterLink *link, AVFilterBufferRef *picref)
 {
-    CropContext *crop = link->dst->priv;
+    AVFilterContext *ctx = link->dst;
+    CropContext *crop = ctx->priv;
     AVFilterBufferRef *ref2 = avfilter_ref_buffer(picref, ~0);
     int i;
 
     picref->video->w = crop->w;
     picref->video->h = crop->h;
 
+    /* FIXME: when the TB will be settable */
+    crop->var_values[T]   = (double)picref->pts / AV_TIME_BASE;
+    crop->var_values[POS] = picref->pos;
+    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
+    crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
+    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
+
+    if (isnan(crop->var_values[X]) || isnan(crop->var_values[Y])) {
+        av_log(ctx, AV_LOG_DEBUG, "Invalid evaluated values for x or y, keeping the previously set values.\n");
+    } else {
+        crop->x = crop->var_values[X];
+        crop->y = crop->var_values[Y];
+    }
+
+    if (crop->x < 0) crop->x = 0;
+    if (crop->y < 0) crop->y = 0;
+    if ((unsigned)crop->x + (unsigned)crop->w > link->w) crop->x = link->w - crop->w;
+    if ((unsigned)crop->y + (unsigned)crop->h > link->h) crop->y = link->h - crop->h;
+    crop->x &= ~((1 << crop->hsub) - 1);
+    crop->y &= ~((1 << crop->vsub) - 1);
+
+    av_log(ctx, AV_LOG_DEBUG,
+           "n:%d t:%f x:%d y:%d x+w:%d y+h:%d\n",
+           (int)crop->var_values[N], crop->var_values[T], crop->x, crop->y, crop->x+crop->w, crop->y+crop->h);
+
     ref2->data[0] += crop->y * ref2->linesize[0];
     ref2->data[0] += (crop->x * crop->max_step[0]);
 
@@ -170,6 +282,14 @@ static void draw_slice(AVFilterLink *link, int y, int h, int slice_dir)
     avfilter_draw_slice(ctx->outputs[0], y - crop->y, h, slice_dir);
 }
 
+static void end_frame(AVFilterLink *link)
+{
+    CropContext *crop = link->dst->priv;
+
+    crop->var_values[N] += 1.0;
+    avfilter_end_frame(link->dst->outputs[0]);
+}
+
 AVFilter avfilter_vf_crop = {
     .name      = "crop",
     .description = NULL_IF_CONFIG_SMALL("Crop the input video to x:y:width:height."),
@@ -178,11 +298,13 @@ AVFilter avfilter_vf_crop = {
 
     .query_formats = query_formats,
     .init          = init,
+    .uninit        = uninit,
 
     .inputs    = (AVFilterPad[]) {{ .name             = "default",
                                     .type             = AVMEDIA_TYPE_VIDEO,
                                     .start_frame      = start_frame,
                                     .draw_slice       = draw_slice,
+                                    .end_frame        = end_frame,
                                     .get_video_buffer = avfilter_null_get_video_buffer,
                                     .config_props     = config_input, },
                                   { .name = NULL}},
-- 
1.7.1


--y0ulUmNC+osPPQO6--



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