vf_mpdecimate.c

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/*
 * Copyright (c) 2003 Rich Felker
 * Copyright (c) 2012 Stefano Sabatini
 * Copyright (c) 2026 Dawid Stachowiak
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 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 General Public License for more details.
 *
 * You should have received a copy of the GNU 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.
 */
 
/**
 * @file mpdecimate filter, ported from libmpcodecs/vf_decimate.c by
 * Rich Felker.
 */
 
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
#include "libavutil/pixelutils.h"
#include "libavutil/timestamp.h"
#include "avfilter.h"
#include "filters.h"
#include "video.h"
 
typedef enum {
    DECIMATE_DROP,          ///< similar frame, past keep threshold — drop it
    DECIMATE_KEEP_UPDATE,   ///< keep frame and update reference (frame is different, or first frame)
    DECIMATE_KEEP_NO_UPDATE,///< keep frame without updating reference (similar frame under keep threshold, or forced keep due to max_drop_count)
} DecimateResult;
 
typedef struct DecimateContext {
    const AVClass *class;
    int mode;                      ///< 0: drop similar frames, 1: drop similar and unique frames
    int lo, hi;                    ///< lower and higher threshold number of differences
                                   ///< values for 8x8 blocks
 
    float frac;                    ///< threshold of changed pixels over the total fraction
 
    int max_drop_count;            ///< for mode 0: if positive: maximum number of sequential frames to drop
                                   ///< for mode 0: if negative: minimum number of frames between two drops
 
    int drop_count;                ///< if positive: number of frames sequentially dropped
                                   ///< if negative: number of sequential frames which were not dropped
 
    int max_keep_count;            ///< for mode 0: number of similar frames to ignore before to start dropping them
    int keep_count;                ///< for mode 0: number of similar frames already ignored
 
    int min_dup_count;             ///< for mode 1: minimum number of previous frames that need to be duplicated to keep frame
    int dup_count;                 ///< for mode 1: number of duplicated frames
 
    int hsub, vsub;                ///< chroma subsampling values
    AVFrame *ref;                  ///< reference picture
    av_pixelutils_sad_fn sad;      ///< sum of absolute difference function
} DecimateContext;
 
#define OFFSET(x) offsetof(DecimateContext, x)
#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
 
static const AVOption mpdecimate_options[] = {
    { "max",  "for mode 0: set the maximum number of consecutive dropped frames (positive), or the minimum interval between dropped frames (negative)",
      OFFSET(max_drop_count), AV_OPT_TYPE_INT, {.i64=0}, INT_MIN, INT_MAX, FLAGS },
    { "keep", "for mode 0: set the number of similar consecutive frames to be kept before starting to drop similar frames",
      OFFSET(max_keep_count), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS },
    { "hi",   "set high dropping threshold", OFFSET(hi), AV_OPT_TYPE_INT, {.i64=64*12}, INT_MIN, INT_MAX, FLAGS },
    { "lo",   "set low dropping threshold", OFFSET(lo), AV_OPT_TYPE_INT, {.i64=64*5}, INT_MIN, INT_MAX, FLAGS },
    { "frac", "set fraction dropping threshold",  OFFSET(frac), AV_OPT_TYPE_FLOAT, {.dbl=0.33}, 0, 1, FLAGS },
    { "mode", "0: drop similar frames, 1: drop similar and unique frames", OFFSET(mode), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS },
    { "min",  "for mode 1: set minimum number of previous frames that need to be duplicated to keep current frame",
      OFFSET(min_dup_count), AV_OPT_TYPE_INT, {.i64=1}, 1, INT_MAX, FLAGS },
    { NULL }
};
 
AVFILTER_DEFINE_CLASS(mpdecimate);
 
/**
 * Return 1 if the two planes are different, 0 otherwise.
 */
static int diff_planes(AVFilterContext *ctx,
                       uint8_t *cur, int cur_linesize,
                       uint8_t *ref, int ref_linesize,
                       int w, int h)
{
    DecimateContext *decimate = ctx->priv;
 
    int x, y;
    int d, c = 0;
    int t = (w/16)*(h/16)*decimate->frac;
 
    /* compute difference for blocks of 8x8 bytes */
    for (y = 0; y < h-7; y += 4) {
        for (x = 8; x < w-7; x += 4) {
            d = decimate->sad(cur + y*cur_linesize + x, cur_linesize,
                              ref + y*ref_linesize + x, ref_linesize);
            if (d > decimate->hi) {
                av_log(ctx, AV_LOG_DEBUG, "%d>=hi ", d);
                return 1;
            }
            if (d > decimate->lo) {
                c++;
                if (c > t) {
                    av_log(ctx, AV_LOG_DEBUG, "lo:%d>=%d ", c, t);
                    return 1;
                }
            }
        }
    }
 
    av_log(ctx, AV_LOG_DEBUG, "lo:%d<%d ", c, t);
    return 0;
}
 
/**
 * Tell if the frame is different with respect to the reference frame ref.
 */
static int is_frame_different(AVFilterContext *ctx,
                              AVFrame *cur, AVFrame *ref)
{
    DecimateContext *decimate = ctx->priv;
    int plane;
 
    for (plane = 0; ref->data[plane] && ref->linesize[plane]; plane++) {
        /* use 8x8 SAD even on subsampled planes.  The blocks won't match up with
         * luma blocks, but hopefully nobody is depending on this to catch
         * localized chroma changes that wouldn't exceed the thresholds when
         * diluted by using what's effectively a larger block size.
         */
        int vsub = plane == 1 || plane == 2 ? decimate->vsub : 0;
        int hsub = plane == 1 || plane == 2 ? decimate->hsub : 0;
        if (diff_planes(ctx,
                        cur->data[plane], cur->linesize[plane],
                        ref->data[plane], ref->linesize[plane],
                        AV_CEIL_RSHIFT(ref->width, hsub),
                        AV_CEIL_RSHIFT(ref->height, vsub)))
            return 1;
    }
 
    return 0;
}
 
/**
 * Tell if the frame should be decimated, for example if it is no much
 * different with respect to the reference frame ref.
 */
static DecimateResult decimate_frame(AVFilterContext *ctx, AVFrame *cur, AVFrame *ref)
{
    DecimateContext *decimate = ctx->priv;
    int is_similar = is_frame_different(ctx, cur, ref) == 0;
 
    if (!is_similar) {
        return DECIMATE_KEEP_UPDATE;
    }
    /* Frame is similar - check if we must keep it due to drop limits */
    if (decimate->max_drop_count > 0 &&
        decimate->drop_count >= decimate->max_drop_count)
        return DECIMATE_KEEP_NO_UPDATE;
    if (decimate->max_drop_count < 0 &&
        (decimate->drop_count - 1) > decimate->max_drop_count)
        return DECIMATE_KEEP_NO_UPDATE;
 
    /* Frame is similar - check if we must keep it due to keep option */
    if (decimate->max_keep_count > 0 && decimate->keep_count > -1 &&
        decimate->keep_count < decimate->max_keep_count) {
        decimate->keep_count++;
        return DECIMATE_KEEP_NO_UPDATE;
    }
    return DECIMATE_DROP;
}
 
static av_cold int init(AVFilterContext *ctx)
{
    DecimateContext *decimate = ctx->priv;
 
    decimate->sad = av_pixelutils_get_sad_fn(3, 3, 0, ctx); // 8x8, not aligned on blocksize
    if (!decimate->sad)
        return AVERROR(EINVAL);
 
    if (decimate->mode == 1) {
        av_log(ctx, AV_LOG_VERBOSE, "min_dup_count:%d hi:%d lo:%d frac:%f\n",
           decimate->min_dup_count, decimate->hi, decimate->lo,
           decimate->frac);
    } else {
        av_log(ctx, AV_LOG_VERBOSE, "max_drop_count:%d hi:%d lo:%d frac:%f\n",
           decimate->max_drop_count, decimate->hi, decimate->lo, decimate->frac);
    }
    return 0;
}
 
static av_cold void uninit(AVFilterContext *ctx)
{
    DecimateContext *decimate = ctx->priv;
    av_frame_free(&decimate->ref);
}
 
static const enum AVPixelFormat pix_fmts[] = {
    AV_PIX_FMT_YUV444P,      AV_PIX_FMT_YUV422P,
    AV_PIX_FMT_YUV420P,      AV_PIX_FMT_YUV411P,
    AV_PIX_FMT_YUV410P,      AV_PIX_FMT_YUV440P,
    AV_PIX_FMT_YUVJ444P,     AV_PIX_FMT_YUVJ422P,
    AV_PIX_FMT_YUVJ420P,     AV_PIX_FMT_YUVJ440P,
    AV_PIX_FMT_YUVA420P,
 
    AV_PIX_FMT_GBRP,
 
    AV_PIX_FMT_YUVA444P,
    AV_PIX_FMT_YUVA422P,
 
    AV_PIX_FMT_NONE
};
 
static int config_input(AVFilterLink *inlink)
{
    AVFilterContext *ctx = inlink->dst;
    DecimateContext *decimate = ctx->priv;
    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(inlink->format);
    decimate->hsub = pix_desc->log2_chroma_w;
    decimate->vsub = pix_desc->log2_chroma_h;
 
    return 0;
}
 
static int filter_frame_mode_0(AVFilterLink *inlink, AVFrame *cur)
{
    DecimateContext *decimate = inlink->dst->priv;
    AVFilterLink *outlink = inlink->dst->outputs[0];
    AVFrame *out = NULL;
    int ret;
    DecimateResult result = decimate->ref ? decimate_frame(inlink->dst, cur, decimate->ref) : DECIMATE_KEEP_UPDATE;
 
    switch (result) {
    case DECIMATE_DROP:
        decimate->drop_count = FFMAX(1, decimate->drop_count+1);
        decimate->keep_count = -1;
        break;
    case DECIMATE_KEEP_NO_UPDATE:
        decimate->drop_count = FFMIN(-1, decimate->drop_count-1);
        out = cur;
        break;
    case DECIMATE_KEEP_UPDATE:
        out = av_frame_clone(cur);
        if (!out) {
            av_frame_free(&cur);
            return AVERROR(ENOMEM);
        }
        av_frame_free(&decimate->ref);
        decimate->ref = cur;
        decimate->drop_count = FFMIN(-1, decimate->drop_count-1);
        decimate->keep_count = 0;
        break;
    }
 
    av_log(inlink->dst, AV_LOG_DEBUG,
           "%s pts:%s pts_time:%s drop_count:%d keep_count:%d\n",
           result == DECIMATE_DROP ? "drop" : "keep",
           av_ts2str(cur->pts), av_ts2timestr(cur->pts, &inlink->time_base),
           decimate->drop_count,
           decimate->keep_count);
 
    if (result == DECIMATE_DROP) {
        av_frame_free(&cur);
        return 0;
    }
 
    ret = ff_filter_frame(outlink, out);
    if (ret < 0)
        return ret;
 
    return 0;
}
 
static int filter_frame_mode_1(AVFilterLink *inlink, AVFrame *cur)
{
    DecimateContext *decimate = inlink->dst->priv;
    AVFilterLink *outlink = inlink->dst->outputs[0];
    int ret;
    AVFrame *out = NULL;
 
    if (!decimate->ref || is_frame_different(inlink->dst, cur, decimate->ref)) {
        AVFrame *ref = av_frame_clone(cur);
        if (!ref) {
            av_frame_free(&cur);
            return AVERROR(ENOMEM);
        }
        av_frame_free(&decimate->ref);
        decimate->ref = ref;
        decimate->dup_count = 0;
    } else {
        decimate->dup_count++;
    }
 
    av_log(inlink->dst, AV_LOG_DEBUG,
           "%s pts:%s pts_time:%s dup_count:%d\n",
           decimate->dup_count ==
           decimate->min_dup_count ? "keep" : "drop", av_ts2str(cur->pts),
           av_ts2timestr(cur->pts, &inlink->time_base),
           decimate->dup_count);
 
    if (decimate->dup_count == decimate->min_dup_count) {
        out = av_frame_clone(decimate->ref);
        if (!out) {
            av_frame_free(&cur);
            return AVERROR(ENOMEM);
        }
        ret = ff_filter_frame(outlink, out);
        if (ret < 0) {
            av_frame_free(&cur);
            return ret;
        }
    }
    av_frame_free(&cur);
 
    return 0;
}
 
static int filter_frame(AVFilterLink *inlink, AVFrame *cur)
{
    DecimateContext *decimate = inlink->dst->priv;
    return decimate->mode == 0 ? filter_frame_mode_0(inlink, cur) : filter_frame_mode_1(inlink, cur);
}
 
static const AVFilterPad mpdecimate_inputs[] = {
    {
        .name         = "default",
        .type         = AVMEDIA_TYPE_VIDEO,
        .config_props = config_input,
        .filter_frame = filter_frame,
    },
};
 
const FFFilter ff_vf_mpdecimate = {
    .p.name        = "mpdecimate",
    .p.description = NULL_IF_CONFIG_SMALL("Remove near-duplicate frames."),
    .p.priv_class  = &mpdecimate_class,
    .init          = init,
    .uninit        = uninit,
    .priv_size     = sizeof(DecimateContext),
    FILTER_INPUTS(mpdecimate_inputs),
    FILTER_OUTPUTS(ff_video_default_filterpad),
    FILTER_PIXFMTS_ARRAY(pix_fmts),
};