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This filter is inspired upon libmpcodecs/vf_framestep.c, by Daniele Forghieri. Only-keyframe output is not supported, since that feature can be achieved through the more versatile select filter.
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/* | ||
* Copyright (c) 2012 Stefano Sabatini | ||
* | ||
* This file is part of FFmpeg. | ||
* | ||
* FFmpeg is free software; you can redistribute it and/or | ||
* modify it under the terms of the GNU Lesser General Public | ||
* License as published by the Free Software Foundation; either | ||
* version 2.1 of the License, or (at your option) any later version. | ||
* | ||
* FFmpeg is distributed in the hope that it will be useful, | ||
* but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
* Lesser General Public License for more details. | ||
* | ||
* You should have received a copy of the GNU Lesser General Public | ||
* License along with FFmpeg; if not, write to the Free Software | ||
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | ||
*/ | ||
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/** | ||
* @file framestep filter, inspired on libmpcodecs/vf_framestep.c by | ||
* Daniele Fornighieri <guru AT digitalfantasy it>. | ||
*/ | ||
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#include "avfilter.h" | ||
#include "internal.h" | ||
#include "video.h" | ||
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typedef struct { | ||
int frame_step, frame_count, frame_selected; | ||
} FrameStepContext; | ||
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static av_cold int init(AVFilterContext *ctx, const char *args) | ||
{ | ||
FrameStepContext *framestep = ctx->priv; | ||
char *tailptr; | ||
long int n; | ||
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framestep->frame_step = 1; | ||
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if (args) { | ||
n = strtol(args, &tailptr, 10); | ||
if (*tailptr || n <= 0 || n >= INT_MAX) { | ||
av_log(ctx, AV_LOG_ERROR, | ||
"Invalid argument '%s', must be a positive integer <= INT_MAX\n", args); | ||
return AVERROR(EINVAL); | ||
} | ||
} | ||
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framestep->frame_step = n; | ||
return 0; | ||
} | ||
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static int config_output_props(AVFilterLink *outlink) | ||
{ | ||
AVFilterContext *ctx = outlink->src; | ||
FrameStepContext *framestep = ctx->priv; | ||
AVFilterLink *inlink = ctx->inputs[0]; | ||
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outlink->frame_rate = | ||
av_div_q(inlink->frame_rate, (AVRational){framestep->frame_step, 1}); | ||
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av_log(ctx, AV_LOG_VERBOSE, "step:%d frame_rate:%d/%d(%f) -> frame_rate:%d/%d(%f)\n", | ||
framestep->frame_step, | ||
inlink->frame_rate.num, inlink->frame_rate.den, av_q2d(inlink->frame_rate), | ||
outlink->frame_rate.num, outlink->frame_rate.den, av_q2d(outlink->frame_rate)); | ||
return 0; | ||
} | ||
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static int start_frame(AVFilterLink *inlink, AVFilterBufferRef *ref) | ||
{ | ||
FrameStepContext *framestep = inlink->dst->priv; | ||
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framestep->frame_selected = 0; | ||
if (!(framestep->frame_count++ % framestep->frame_step)) { | ||
inlink->cur_buf = NULL; | ||
framestep->frame_selected = 1; | ||
return ff_start_frame(inlink->dst->outputs[0], ref); | ||
} | ||
return 0; | ||
} | ||
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static int draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir) | ||
{ | ||
FrameStepContext *framestep = inlink->dst->priv; | ||
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if (framestep->frame_selected) | ||
return ff_draw_slice(inlink->dst->outputs[0], y, h, slice_dir); | ||
return 0; | ||
} | ||
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static int end_frame(AVFilterLink *inlink) | ||
{ | ||
FrameStepContext *framestep = inlink->dst->priv; | ||
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if (framestep->frame_selected) | ||
return ff_end_frame(inlink->dst->outputs[0]); | ||
return 0; | ||
} | ||
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static int request_frame(AVFilterLink *outlink) | ||
{ | ||
FrameStepContext *framestep = outlink->src->priv; | ||
AVFilterLink *inlink = outlink->src->inputs[0]; | ||
int ret; | ||
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framestep->frame_selected = 0; | ||
do { | ||
ret = ff_request_frame(inlink); | ||
} while (!framestep->frame_selected && ret >= 0); | ||
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return ret; | ||
} | ||
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AVFilter avfilter_vf_framestep = { | ||
.name = "framestep", | ||
.description = NULL_IF_CONFIG_SMALL("Select one frame every N frames."), | ||
.init = init, | ||
.priv_size = sizeof(FrameStepContext), | ||
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.inputs = (const AVFilterPad[]) { | ||
{ | ||
.name = "default", | ||
.type = AVMEDIA_TYPE_VIDEO, | ||
.get_video_buffer = ff_null_get_video_buffer, | ||
.start_frame = start_frame, | ||
.draw_slice = draw_slice, | ||
.end_frame = end_frame, | ||
}, | ||
{ .name = NULL } | ||
}, | ||
.outputs = (const AVFilterPad[]) { | ||
{ | ||
.name = "default", | ||
.type = AVMEDIA_TYPE_VIDEO, | ||
.config_props = config_output_props, | ||
.request_frame = request_frame, | ||
}, | ||
{ .name = NULL } | ||
}, | ||
}; |