Libav
vf_crop.c
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1 /*
2  * Copyright (c) 2007 Bobby Bingham
3  *
4  * This file is part of Libav.
5  *
6  * Libav is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * Libav is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with Libav; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
26 #include <stdio.h>
27 
28 #include "avfilter.h"
29 #include "formats.h"
30 #include "internal.h"
31 #include "video.h"
32 #include "libavutil/eval.h"
33 #include "libavutil/avstring.h"
34 #include "libavutil/internal.h"
35 #include "libavutil/libm.h"
36 #include "libavutil/imgutils.h"
37 #include "libavutil/mathematics.h"
38 #include "libavutil/opt.h"
39 
40 static const char *const var_names[] = {
41  "E",
42  "PHI",
43  "PI",
44  "in_w", "iw",
45  "in_h", "ih",
46  "out_w", "ow",
47  "out_h", "oh",
48  "x",
49  "y",
50  "n",
51  "pos",
52  "t",
53  NULL
54 };
55 
56 enum var_name {
69 };
70 
71 typedef struct CropContext {
72  const AVClass *class;
73  int x;
74  int y;
75  int w;
76  int h;
77 
78  int max_step[4];
79  int hsub, vsub;
81  AVExpr *x_pexpr, *y_pexpr; /* parsed expressions for x and y */
83 } CropContext;
84 
86 {
87  static const enum AVPixelFormat pix_fmts[] = {
111  };
112 
114 
115  return 0;
116 }
117 
118 static av_cold void uninit(AVFilterContext *ctx)
119 {
120  CropContext *s = ctx->priv;
121 
122  av_expr_free(s->x_pexpr);
123  s->x_pexpr = NULL;
124  av_expr_free(s->y_pexpr);
125  s->y_pexpr = NULL;
126 }
127 
128 static inline int normalize_double(int *n, double d)
129 {
130  int ret = 0;
131 
132  if (isnan(d)) {
133  ret = AVERROR(EINVAL);
134  } else if (d > INT_MAX || d < INT_MIN) {
135  *n = d > INT_MAX ? INT_MAX : INT_MIN;
136  ret = AVERROR(EINVAL);
137  } else
138  *n = round(d);
139 
140  return ret;
141 }
142 
143 static int config_input(AVFilterLink *link)
144 {
145  AVFilterContext *ctx = link->dst;
146  CropContext *s = ctx->priv;
147  const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(link->format);
148  int ret;
149  const char *expr;
150  double res;
151 
152  s->var_values[VAR_E] = M_E;
153  s->var_values[VAR_PHI] = M_PHI;
154  s->var_values[VAR_PI] = M_PI;
155  s->var_values[VAR_IN_W] = s->var_values[VAR_IW] = ctx->inputs[0]->w;
156  s->var_values[VAR_IN_H] = s->var_values[VAR_IH] = ctx->inputs[0]->h;
157  s->var_values[VAR_X] = NAN;
158  s->var_values[VAR_Y] = NAN;
161  s->var_values[VAR_N] = 0;
162  s->var_values[VAR_T] = NAN;
163 
165  s->hsub = pix_desc->log2_chroma_w;
166  s->vsub = pix_desc->log2_chroma_h;
167 
168  if ((ret = av_expr_parse_and_eval(&res, (expr = s->ow_expr),
169  var_names, s->var_values,
170  NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
171  goto fail_expr;
172  s->var_values[VAR_OUT_W] = s->var_values[VAR_OW] = res;
173  if ((ret = av_expr_parse_and_eval(&res, (expr = s->oh_expr),
174  var_names, s->var_values,
175  NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
176  goto fail_expr;
177  s->var_values[VAR_OUT_H] = s->var_values[VAR_OH] = res;
178  /* evaluate again ow as it may depend on oh */
179  if ((ret = av_expr_parse_and_eval(&res, (expr = s->ow_expr),
180  var_names, s->var_values,
181  NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
182  goto fail_expr;
183 
184  s->var_values[VAR_OUT_W] = s->var_values[VAR_OW] = res;
185  if (normalize_double(&s->w, s->var_values[VAR_OUT_W]) < 0 ||
186  normalize_double(&s->h, s->var_values[VAR_OUT_H]) < 0) {
187  av_log(ctx, AV_LOG_ERROR,
188  "Too big value or invalid expression for out_w/ow or out_h/oh. "
189  "Maybe the expression for out_w:'%s' or for out_h:'%s' is self-referencing.\n",
190  s->ow_expr, s->oh_expr);
191  return AVERROR(EINVAL);
192  }
193  s->w &= ~((1 << s->hsub) - 1);
194  s->h &= ~((1 << s->vsub) - 1);
195 
196  av_expr_free(s->x_pexpr);
197  av_expr_free(s->y_pexpr);
198  s->x_pexpr = s->y_pexpr = NULL;
199  if ((ret = av_expr_parse(&s->x_pexpr, s->x_expr, var_names,
200  NULL, NULL, NULL, NULL, 0, ctx)) < 0 ||
201  (ret = av_expr_parse(&s->y_pexpr, s->y_expr, var_names,
202  NULL, NULL, NULL, NULL, 0, ctx)) < 0)
203  return AVERROR(EINVAL);
204 
205  av_log(ctx, AV_LOG_VERBOSE, "w:%d h:%d -> w:%d h:%d\n",
206  link->w, link->h, s->w, s->h);
207 
208  if (s->w <= 0 || s->h <= 0 ||
209  s->w > link->w || s->h > link->h) {
210  av_log(ctx, AV_LOG_ERROR,
211  "Invalid too big or non positive size for width '%d' or height '%d'\n",
212  s->w, s->h);
213  return AVERROR(EINVAL);
214  }
215 
216  /* set default, required in the case the first computed value for x/y is NAN */
217  s->x = (link->w - s->w) / 2;
218  s->y = (link->h - s->h) / 2;
219  s->x &= ~((1 << s->hsub) - 1);
220  s->y &= ~((1 << s->vsub) - 1);
221  return 0;
222 
223 fail_expr:
224  av_log(NULL, AV_LOG_ERROR, "Error when evaluating the expression '%s'\n", expr);
225  return ret;
226 }
227 
228 static int config_output(AVFilterLink *link)
229 {
230  CropContext *s = link->src->priv;
231 
232  link->w = s->w;
233  link->h = s->h;
234 
235  return 0;
236 }
237 
238 static int filter_frame(AVFilterLink *link, AVFrame *frame)
239 {
240  AVFilterContext *ctx = link->dst;
241  CropContext *s = ctx->priv;
242  const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(link->format);
243  int i;
244 
245  frame->width = s->w;
246  frame->height = s->h;
247 
248  s->var_values[VAR_T] = frame->pts == AV_NOPTS_VALUE ?
249  NAN : frame->pts * av_q2d(link->time_base);
253 
256 
257  if (s->x < 0)
258  s->x = 0;
259  if (s->y < 0)
260  s->y = 0;
261  if ((unsigned)s->x + (unsigned)s->w > link->w)
262  s->x = link->w - s->w;
263  if ((unsigned)s->y + (unsigned)s->h > link->h)
264  s->y = link->h - s->h;
265  s->x &= ~((1 << s->hsub) - 1);
266  s->y &= ~((1 << s->vsub) - 1);
267 
268  av_dlog(ctx, "n:%d t:%f x:%d y:%d x+w:%d y+h:%d\n",
269  (int)s->var_values[VAR_N], s->var_values[VAR_T], s->x,
270  s->y, s->x+s->w, s->y+s->h);
271 
272  frame->data[0] += s->y * frame->linesize[0];
273  frame->data[0] += s->x * s->max_step[0];
274 
275  if (!(desc->flags & AV_PIX_FMT_FLAG_PAL || desc->flags & AV_PIX_FMT_FLAG_PSEUDOPAL)) {
276  for (i = 1; i < 3; i ++) {
277  if (frame->data[i]) {
278  frame->data[i] += (s->y >> s->vsub) * frame->linesize[i];
279  frame->data[i] += (s->x * s->max_step[i]) >> s->hsub;
280  }
281  }
282  }
283 
284  /* alpha plane */
285  if (frame->data[3]) {
286  frame->data[3] += s->y * frame->linesize[3];
287  frame->data[3] += s->x * s->max_step[3];
288  }
289 
290  s->var_values[VAR_N] += 1.0;
291 
292  return ff_filter_frame(link->dst->outputs[0], frame);
293 }
294 
295 #define OFFSET(x) offsetof(CropContext, x)
296 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM
297 static const AVOption options[] = {
298  { "out_w", "Output video width", OFFSET(ow_expr), AV_OPT_TYPE_STRING, { .str = "iw" }, .flags = FLAGS },
299  { "out_h", "Output video height", OFFSET(oh_expr), AV_OPT_TYPE_STRING, { .str = "ih" }, .flags = FLAGS },
300  { "x", "Horizontal position in the input video of the left edge of the cropped output video",
301  OFFSET(x_expr), AV_OPT_TYPE_STRING, { .str = "(in_w - out_w) / 2" }, .flags = FLAGS },
302  { "y", "Vertical position in the input video of the top edge of the cropped output video",
303  OFFSET(y_expr), AV_OPT_TYPE_STRING, { .str = "(in_h - out_h) / 2" }, .flags = FLAGS },
304  { NULL },
305 };
306 
307 static const AVClass crop_class = {
308  .class_name = "crop",
309  .item_name = av_default_item_name,
310  .option = options,
311  .version = LIBAVUTIL_VERSION_INT,
312 };
313 
315  {
316  .name = "default",
317  .type = AVMEDIA_TYPE_VIDEO,
318  .filter_frame = filter_frame,
319  .get_video_buffer = ff_null_get_video_buffer,
320  .config_props = config_input,
321  },
322  { NULL }
323 };
324 
326  {
327  .name = "default",
328  .type = AVMEDIA_TYPE_VIDEO,
329  .config_props = config_output,
330  },
331  { NULL }
332 };
333 
335  .name = "crop",
336  .description = NULL_IF_CONFIG_SMALL("Crop the input video to width:height:x:y."),
337 
338  .priv_size = sizeof(CropContext),
339  .priv_class = &crop_class,
340 
342  .uninit = uninit,
343 
344  .inputs = avfilter_vf_crop_inputs,
345  .outputs = avfilter_vf_crop_outputs,
346 };
#define AV_PIX_FMT_FLAG_PAL
Pixel format has a palette in data[1], values are indexes in this palette.
Definition: pixdesc.h:112
AVExpr * x_pexpr
Definition: vf_crop.c:81
const AVPixFmtDescriptor * av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
Definition: pixdesc.c:1599
This structure describes decoded (raw) audio or video data.
Definition: frame.h:135
#define FLAGS
Definition: vf_crop.c:296
AVOption.
Definition: opt.h:234
static int config_input(AVFilterLink *link)
Definition: vf_crop.c:143
planar YUV 4:4:4, 24bpp, (1 Cr & Cb sample per 1x1 Y samples)
Definition: pixfmt.h:70
misc image utilities
static const AVFilterPad outputs[]
Definition: af_ashowinfo.c:232
Main libavfilter public API header.
packed RGB 8:8:8, 24bpp, RGBRGB...
Definition: pixfmt.h:67
packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), little-endian, most significant bit to 0 ...
Definition: pixfmt.h:118
AVFrame * ff_null_get_video_buffer(AVFilterLink *link, int w, int h)
Definition: video.c:30
packed BGR 5:6:5, 16bpp, (msb) 5B 6G 5R(lsb), little-endian
Definition: pixfmt.h:121
av_dlog(ac->avr,"%d samples - audio_convert: %s to %s (%s)\n", len, av_get_sample_fmt_name(ac->in_fmt), av_get_sample_fmt_name(ac->out_fmt), use_generic?ac->func_descr_generic:ac->func_descr)
int av_expr_parse(AVExpr **expr, const char *s, const char *const *const_names, const char *const *func1_names, double(*const *funcs1)(void *, double), const char *const *func2_names, double(*const *funcs2)(void *, double, double), int log_offset, void *log_ctx)
Parse an expression.
Definition: eval.c:492
Definition: vf_crop.c:59
planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian
Definition: pixfmt.h:129
uint8_t log2_chroma_w
Amount to shift the luma width right to find the chroma width.
Definition: pixdesc.h:80
AVFilter ff_vf_crop
Definition: vf_crop.c:334
AVFilterFormats * ff_make_format_list(const int *fmts)
Create a list of supported formats.
Definition: formats.c:165
packed RGB 5:6:5, 16bpp, (msb) 5R 6G 5B(lsb), little-endian
Definition: pixfmt.h:116
Definition: vf_crop.c:62
packed RGB 1:2:1, 8bpp, (msb)1B 2G 1R(lsb)
Definition: pixfmt.h:88
void av_image_fill_max_pixsteps(int max_pixsteps[4], int max_pixstep_comps[4], const AVPixFmtDescriptor *pixdesc)
Compute the max pixel step for each plane of an image with a format described by pixdesc.
Definition: imgutils.c:32
const char * name
Pad name.
Definition: internal.h:42
const char * class_name
The name of the class; usually it is the same name as the context structure type to which the AVClass...
Definition: log.h:38
AVFilterLink ** inputs
array of pointers to input links
Definition: avfilter.h:571
int ff_filter_frame(AVFilterLink *link, AVFrame *frame)
Send a frame of data to the next filter.
Definition: avfilter.c:728
planar YUV 4:2:0, 20bpp, (1 Cr & Cb sample per 2x2 Y & A samples)
Definition: pixfmt.h:104
#define av_cold
Definition: attributes.h:66
int x
x offset of the non-cropped area with respect to the input area
Definition: vf_crop.c:73
8 bit with PIX_FMT_RGB32 palette
Definition: pixfmt.h:76
AVOptions.
packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as lit...
Definition: pixfmt.h:113
int y
y offset of the non-cropped area with respect to the input area
Definition: vf_crop.c:74
static av_always_inline av_const int isnan(float x)
Definition: libm.h:85
Definition: vf_crop.c:57
int max_step[4]
max pixel step for each plane, expressed as a number of bytes
Definition: vf_crop.c:78
int64_t pts
Presentation timestamp in time_base units (time when frame should be shown to user).
Definition: frame.h:211
Definition: eval.c:128
packed RGB 5:6:5, 16bpp, (msb) 5R 6G 5B(lsb), big-endian
Definition: pixfmt.h:115
static const AVFilterPad avfilter_vf_crop_outputs[]
Definition: vf_crop.c:325
packed ABGR 8:8:8:8, 32bpp, ABGRABGR...
Definition: pixfmt.h:97
static double av_q2d(AVRational a)
Convert rational to double.
Definition: rational.h:69
planar YUV 4:4:0 full scale (JPEG), deprecated in favor of PIX_FMT_YUV440P and setting color_range ...
Definition: pixfmt.h:103
planar YUV 4:2:2, 16bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV422P and setting color_...
Definition: pixfmt.h:78
Definition: vf_crop.c:61
#define AV_LOG_VERBOSE
Detailed information.
Definition: log.h:139
static const AVFilterPad avfilter_vf_crop_inputs[]
Definition: vf_crop.c:314
void ff_set_common_formats(AVFilterContext *ctx, AVFilterFormats *formats)
A helper for query_formats() which sets all links to the same list of formats.
Definition: formats.c:379
A filter pad used for either input or output.
Definition: internal.h:36
int hsub
Definition: vf_crop.c:79
int av_expr_parse_and_eval(double *d, const char *s, const char *const *const_names, const double *const_values, const char *const *func1_names, double(*const *funcs1)(void *, double), const char *const *func2_names, double(*const *funcs2)(void *, double, double), void *opaque, int log_offset, void *log_ctx)
Parse and evaluate an expression.
Definition: eval.c:551
int width
width and height of the video frame
Definition: frame.h:174
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:123
uint8_t log2_chroma_h
Amount to shift the luma height right to find the chroma height.
Definition: pixdesc.h:89
Definition: vf_crop.c:66
planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian
Definition: pixfmt.h:134
double var_values[VAR_VARS_NB]
Definition: vf_crop.c:82
#define AVERROR(e)
Definition: error.h:43
#define NULL_IF_CONFIG_SMALL(x)
Return NULL if CONFIG_SMALL is true, otherwise the argument without modification. ...
Definition: internal.h:150
packed BGRA 8:8:8:8, 32bpp, BGRABGRA...
Definition: pixfmt.h:98
void * priv
private data for use by the filter
Definition: avfilter.h:584
void av_log(void *avcl, int level, const char *fmt,...)
Definition: log.c:168
static av_always_inline av_const double round(double x)
Definition: libm.h:151
planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian
Definition: pixfmt.h:132
packed ARGB 8:8:8:8, 32bpp, ARGBARGB...
Definition: pixfmt.h:95
packed RGB 16:16:16, 48bpp, 16B, 16G, 16R, the 2-byte value for each R/G/B component is stored as lit...
Definition: pixfmt.h:149
packed RGBA 8:8:8:8, 32bpp, RGBARGBA...
Definition: pixfmt.h:96
static const AVClass crop_class
Definition: vf_crop.c:307
planar YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples)
Definition: pixfmt.h:69
common internal API header
packed RGB 1:2:1, 8bpp, (msb)1R 2G 1B(lsb)
Definition: pixfmt.h:91
planar YUV 4:2:0, 12bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV420P and setting color_...
Definition: pixfmt.h:77
char * x_expr
Definition: vf_crop.c:80
#define M_E
Definition: ratecontrol.c:39
#define AV_PIX_FMT_FLAG_PSEUDOPAL
The pixel format is "pseudo-paletted".
Definition: pixdesc.h:134
packed RGB 8:8:8, 24bpp, BGRBGR...
Definition: pixfmt.h:68
#define OFFSET(x)
Definition: vf_crop.c:295
AVExpr * y_pexpr
Definition: vf_crop.c:81
static int query_formats(AVFilterContext *ctx)
Definition: vf_crop.c:85
packed RGB 16:16:16, 48bpp, 16B, 16G, 16R, the 2-byte value for each R/G/B component is stored as big...
Definition: pixfmt.h:148
LIBAVUTIL_VERSION_INT
Definition: eval.c:55
packed BGR 5:6:5, 16bpp, (msb) 5B 6G 5R(lsb), big-endian
Definition: pixfmt.h:120
int h
height of the cropped area
Definition: vf_crop.c:76
int vsub
chroma subsampling
Definition: vf_crop.c:79
NULL
Definition: eval.c:55
packed RGB 3:3:2, 8bpp, (msb)2B 3G 3R(lsb)
Definition: pixfmt.h:86
planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian
Definition: pixfmt.h:130
Definition: vf_crop.c:64
void av_expr_free(AVExpr *e)
Free a parsed expression previously created with av_expr_parse().
Definition: eval.c:195
int linesize[AV_NUM_DATA_POINTERS]
For video, size in bytes of each picture line.
Definition: frame.h:153
av_default_item_name
Definition: dnxhdenc.c:52
uint8_t flags
Definition: pixdesc.h:90
Descriptor that unambiguously describes how the bits of a pixel are stored in the up to 4 data planes...
Definition: pixdesc.h:69
static av_cold void uninit(AVFilterContext *ctx)
Definition: vf_crop.c:118
char * oh_expr
Definition: vf_crop.c:80
Definition: vf_crop.c:60
Replacements for frequently missing libm functions.
planar YUV 4:1:0, 9bpp, (1 Cr & Cb sample per 4x4 Y samples)
Definition: pixfmt.h:71
Describe the class of an AVClass context structure.
Definition: log.h:33
Filter definition.
Definition: avfilter.h:421
Y , 16bpp, big-endian.
Definition: pixfmt.h:100
static const AVFilterPad inputs[]
Definition: af_ashowinfo.c:221
#define M_PHI
Definition: mathematics.h:34
char * ow_expr
Definition: vf_crop.c:80
const char * name
Filter name.
Definition: avfilter.h:425
packed BGR 5:5:5, 16bpp, (msb)1A 5B 5G 5R(lsb), little-endian, most significant bit to 1 ...
Definition: pixfmt.h:123
AVFilterLink ** outputs
array of pointers to output links
Definition: avfilter.h:578
Definition: vf_crop.c:63
static const char *const var_names[]
Definition: vf_crop.c:40
packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), big-endian, most significant bit to 0 ...
Definition: pixfmt.h:117
uint8_t * data[AV_NUM_DATA_POINTERS]
pointer to the picture/channel planes.
Definition: frame.h:141
planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian
Definition: pixfmt.h:133
planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per 2x2 Y samples)
Definition: pixfmt.h:65
Y , 8bpp.
Definition: pixfmt.h:73
static int normalize_double(int *n, double d)
Definition: vf_crop.c:128
static int config_output(AVFilterLink *link)
Definition: vf_crop.c:228
Definition: vf_crop.c:65
packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as big...
Definition: pixfmt.h:112
planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian
Definition: pixfmt.h:131
planar YUV 4:4:4, 24bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV444P and setting color_...
Definition: pixfmt.h:79
packed RGB 3:3:2, 8bpp, (msb)2R 3G 3B(lsb)
Definition: pixfmt.h:89
planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y samples)
Definition: pixfmt.h:72
Definition: vf_crop.c:67
#define NAN
Definition: math.h:28
double av_expr_eval(AVExpr *e, const double *const_values, void *opaque)
Evaluate a previously parsed expression.
Definition: eval.c:542
Y , 16bpp, little-endian.
Definition: pixfmt.h:101
An instance of a filter.
Definition: avfilter.h:563
packed BGR 5:5:5, 16bpp, (msb)1A 5B 5G 5R(lsb), big-endian, most significant bit to 1 ...
Definition: pixfmt.h:122
int height
Definition: frame.h:174
planar YUV 4:4:0 (1 Cr & Cb sample per 1x2 Y samples)
Definition: pixfmt.h:102
static const AVOption options[]
Definition: vf_crop.c:297
int w
width of the cropped area
Definition: vf_crop.c:75
internal API functions
AVPixelFormat
Pixel format.
Definition: pixfmt.h:63
var_name
Definition: setpts.c:60
#define AV_NOPTS_VALUE
Undefined timestamp value.
Definition: avutil.h:228
simple arithmetic expression evaluator
static int filter_frame(AVFilterLink *link, AVFrame *frame)
Definition: vf_crop.c:238
char * y_expr
Definition: vf_crop.c:80