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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 "libavutil/opt.h"
  27. #include "avfilter.h"
  28. #include "internal.h"
  29. #include "video.h"
  30.  
  31. typedef struct {
  32.     const AVClass *class;
  33.     int frame_step;
  34. } FrameStepContext;
  35.  
  36. #define OFFSET(x) offsetof(FrameStepContext, x)
  37. #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
  38.  
  39. static const AVOption framestep_options[] = {
  40.     { "step", "set frame step",  OFFSET(frame_step), AV_OPT_TYPE_INT, {.i64=1}, 1, INT_MAX, FLAGS},
  41.     { NULL },
  42. };
  43.  
  44. AVFILTER_DEFINE_CLASS(framestep);
  45.  
  46. static int config_output_props(AVFilterLink *outlink)
  47. {
  48.     AVFilterContext *ctx = outlink->src;
  49.     FrameStepContext *framestep = ctx->priv;
  50.     AVFilterLink *inlink = ctx->inputs[0];
  51.  
  52.     outlink->flags |= FF_LINK_FLAG_REQUEST_LOOP;
  53.     outlink->frame_rate =
  54.         av_div_q(inlink->frame_rate, (AVRational){framestep->frame_step, 1});
  55.  
  56.     av_log(ctx, AV_LOG_VERBOSE, "step:%d frame_rate:%d/%d(%f) -> frame_rate:%d/%d(%f)\n",
  57.            framestep->frame_step,
  58.            inlink->frame_rate.num, inlink->frame_rate.den, av_q2d(inlink->frame_rate),
  59.            outlink->frame_rate.num, outlink->frame_rate.den, av_q2d(outlink->frame_rate));
  60.     return 0;
  61. }
  62.  
  63. static int filter_frame(AVFilterLink *inlink, AVFrame *ref)
  64. {
  65.     FrameStepContext *framestep = inlink->dst->priv;
  66.  
  67.     if (!(inlink->frame_count % framestep->frame_step)) {
  68.         return ff_filter_frame(inlink->dst->outputs[0], ref);
  69.     } else {
  70.         av_frame_free(&ref);
  71.         return 0;
  72.     }
  73. }
  74.  
  75. static const AVFilterPad framestep_inputs[] = {
  76.     {
  77.         .name         = "default",
  78.         .type         = AVMEDIA_TYPE_VIDEO,
  79.         .filter_frame = filter_frame,
  80.     },
  81.     { NULL }
  82. };
  83.  
  84. static const AVFilterPad framestep_outputs[] = {
  85.     {
  86.         .name         = "default",
  87.         .type         = AVMEDIA_TYPE_VIDEO,
  88.         .config_props = config_output_props,
  89.     },
  90.     { NULL }
  91. };
  92.  
  93. AVFilter avfilter_vf_framestep = {
  94.     .name        = "framestep",
  95.     .description = NULL_IF_CONFIG_SMALL("Select one frame every N frames."),
  96.     .priv_size   = sizeof(FrameStepContext),
  97.     .priv_class  = &framestep_class,
  98.     .inputs      = framestep_inputs,
  99.     .outputs     = framestep_outputs,
  100.     .flags       = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
  101. };
  102.