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vf_framestep.c
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1 /*
2  * Copyright (c) 2012 Stefano Sabatini
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg 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  * FFmpeg 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 FFmpeg; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 /**
22  * @file framestep filter, inspired on libmpcodecs/vf_framestep.c by
23  * Daniele Fornighieri <guru AT digitalfantasy it>.
24  */
25 
26 #include "avfilter.h"
27 #include "internal.h"
28 #include "video.h"
29 
30 typedef struct {
31  int frame_step, frame_count, frame_selected;
33 
34 static av_cold int init(AVFilterContext *ctx, const char *args)
35 {
36  FrameStepContext *framestep = ctx->priv;
37  char *tailptr;
38  long int n = 1;
39 
40  if (args) {
41  n = strtol(args, &tailptr, 10);
42  if (*tailptr || n <= 0 || n >= INT_MAX) {
43  av_log(ctx, AV_LOG_ERROR,
44  "Invalid argument '%s', must be a positive integer <= INT_MAX\n", args);
45  return AVERROR(EINVAL);
46  }
47  }
48 
49  framestep->frame_step = n;
50  return 0;
51 }
52 
53 static int config_output_props(AVFilterLink *outlink)
54 {
55  AVFilterContext *ctx = outlink->src;
56  FrameStepContext *framestep = ctx->priv;
57  AVFilterLink *inlink = ctx->inputs[0];
58 
59  outlink->frame_rate =
60  av_div_q(inlink->frame_rate, (AVRational){framestep->frame_step, 1});
61 
62  av_log(ctx, AV_LOG_VERBOSE, "step:%d frame_rate:%d/%d(%f) -> frame_rate:%d/%d(%f)\n",
63  framestep->frame_step,
64  inlink->frame_rate.num, inlink->frame_rate.den, av_q2d(inlink->frame_rate),
65  outlink->frame_rate.num, outlink->frame_rate.den, av_q2d(outlink->frame_rate));
66  return 0;
67 }
68 
69 static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *ref)
70 {
71  FrameStepContext *framestep = inlink->dst->priv;
72 
73  if (!(framestep->frame_count++ % framestep->frame_step)) {
74  framestep->frame_selected = 1;
75  return ff_filter_frame(inlink->dst->outputs[0], ref);
76  } else {
77  framestep->frame_selected = 0;
79  return 0;
80  }
81 }
82 
83 static int request_frame(AVFilterLink *outlink)
84 {
85  FrameStepContext *framestep = outlink->src->priv;
86  AVFilterLink *inlink = outlink->src->inputs[0];
87  int ret;
88 
89  framestep->frame_selected = 0;
90  do {
91  ret = ff_request_frame(inlink);
92  } while (!framestep->frame_selected && ret >= 0);
93 
94  return ret;
95 }
96 
97 static const AVFilterPad framestep_inputs[] = {
98  {
99  .name = "default",
100  .type = AVMEDIA_TYPE_VIDEO,
101  .get_video_buffer = ff_null_get_video_buffer,
102  .filter_frame = filter_frame,
103  },
104  { NULL }
105 };
106 
107 static const AVFilterPad framestep_outputs[] = {
108  {
109  .name = "default",
110  .type = AVMEDIA_TYPE_VIDEO,
111  .config_props = config_output_props,
112  .request_frame = request_frame,
113  },
114  { NULL }
115 };
116 
118  .name = "framestep",
119  .description = NULL_IF_CONFIG_SMALL("Select one frame every N frames."),
120  .init = init,
121  .priv_size = sizeof(FrameStepContext),
122  .inputs = framestep_inputs,
123  .outputs = framestep_outputs,
124 };