vf_blackframe.c

/*
 * Copyright (c) 2010 Stefano Sabatini
 * Copyright (c) 2006 Ivo van Poorten
 * Copyright (c) 2006 Julian Hall
 * Copyright (c) 2002-2003 Brian J. Murrell
 *
 * 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
 * Search for black frames to detect scene transitions.
 * Ported from MPlayer libmpcodecs/vf_blackframe.c.
 */

#include <stdio.h>
#include <inttypes.h>

#include "libavutil/internal.h"
#include "libavutil/opt.h"
#include "avfilter.h"
#include "internal.h"
#include "video.h"

typedef struct BlackFrameContext {
    const AVClass *class;
    int bamount;          ///< black amount
    int bthresh;          ///< black threshold
    unsigned int frame;   ///< frame number
    unsigned int nblack;  ///< number of black pixels counted so far
    unsigned int last_keyframe; ///< frame number of the last received key-frame
} BlackFrameContext;

static const enum AVPixelFormat pix_fmts[] = {
    AV_PIX_FMT_YUV410P, AV_PIX_FMT_YUV420P, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NV12,
    AV_PIX_FMT_NV21, AV_PIX_FMT_YUV444P, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV411P,
    AV_PIX_FMT_NONE
};

#define SET_META(key, format, value) \
    snprintf(buf, sizeof(buf), format, value);  \
    av_dict_set(metadata, key, buf, 0)

static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
{
    AVFilterContext *ctx = inlink->dst;
    BlackFrameContext *s = ctx->priv;
    int x, i;
    int pblack = 0;
    uint8_t *p = frame->data[0];
    AVDictionary **metadata;
    char buf[32];

    for (i = 0; i < frame->height; i++) {
        for (x = 0; x < inlink->w; x++)
            s->nblack += p[x] < s->bthresh;
        p += frame->linesize[0];
    }

    if (frame->flags & AV_FRAME_FLAG_KEY)
        s->last_keyframe = s->frame;

    pblack = s->nblack * 100 / (inlink->w * inlink->h);
    if (pblack >= s->bamount) {
        metadata = &frame->metadata;

        av_log(ctx, AV_LOG_INFO, "frame:%u pblack:%u pts:%"PRId64" t:%f "
               "type:%c last_keyframe:%d\n",
               s->frame, pblack, frame->pts,
               frame->pts == AV_NOPTS_VALUE ? -1 : frame->pts * av_q2d(inlink->time_base),
               av_get_picture_type_char(frame->pict_type), s->last_keyframe);

        SET_META("lavfi.blackframe.pblack", "%u", pblack);
    }

    s->frame++;
    s->nblack = 0;
    return ff_filter_frame(inlink->dst->outputs[0], frame);
}

#define OFFSET(x) offsetof(BlackFrameContext, x)
#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
static const AVOption blackframe_options[] = {
    { "amount", "percentage of the pixels that have to be below the threshold "
        "for the frame to be considered black",  OFFSET(bamount), AV_OPT_TYPE_INT, { .i64 = 98 }, 0, 100,     FLAGS },
    { "threshold", "threshold below which a pixel value is considered black",
                                                 OFFSET(bthresh), AV_OPT_TYPE_INT, { .i64 = 32 }, 0, 255,     FLAGS },
    { "thresh", "threshold below which a pixel value is considered black",
                                                 OFFSET(bthresh), AV_OPT_TYPE_INT, { .i64 = 32 }, 0, 255,     FLAGS },
    { NULL }
};

AVFILTER_DEFINE_CLASS(blackframe);

static const AVFilterPad avfilter_vf_blackframe_inputs[] = {
    {
        .name         = "default",
        .type         = AVMEDIA_TYPE_VIDEO,
        .filter_frame = filter_frame,
    },
};

const AVFilter ff_vf_blackframe = {
    .name          = "blackframe",
    .description   = NULL_IF_CONFIG_SMALL("Detect frames that are (almost) black."),
    .priv_size     = sizeof(BlackFrameContext),
    .priv_class    = &blackframe_class,
    .flags         = AVFILTER_FLAG_METADATA_ONLY,
    FILTER_INPUTS(avfilter_vf_blackframe_inputs),
    FILTER_OUTPUTS(ff_video_default_filterpad),
    FILTER_PIXFMTS_ARRAY(pix_fmts),
};