FFmpeg/libavfilter/vf_select.c

/*
 * Copyright (c) 2011 Stefano Sabatini
 *
 * This file is part of Libav.
 *
 * Libav 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.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * filter for selecting which frame passes in the filterchain
 */

#include "libavutil/eval.h"
#include "libavutil/fifo.h"
#include "libavutil/internal.h"
#include "libavutil/mathematics.h"
#include "libavutil/opt.h"
#include "avfilter.h"
#include "internal.h"
#include "video.h"

static const char *const var_names[] = {
    "E",                 ///< Euler number
    "PHI",               ///< golden ratio
    "PI",                ///< greek pi

    "TB",                ///< timebase

    "pts",               ///< original pts in the file of the frame
    "start_pts",         ///< first PTS in the stream, expressed in TB units
    "prev_pts",          ///< previous frame PTS
    "prev_selected_pts", ///< previous selected frame PTS

    "t",                 ///< first PTS in seconds
    "start_t",           ///< first PTS in the stream, expressed in seconds
    "prev_t",            ///< previous frame time
    "prev_selected_t",   ///< previously selected time

    "pict_type",         ///< the type of picture in the movie
    "I",
    "P",
    "B",
    "S",
    "SI",
    "SP",
    "BI",

    "interlace_type",    ///< the frame interlace type
    "PROGRESSIVE",
    "TOPFIRST",
    "BOTTOMFIRST",

    "n",                 ///< frame number (starting from zero)
    "selected_n",        ///< selected frame number (starting from zero)
    "prev_selected_n",   ///< number of the last selected frame

    "key",               ///< tell if the frame is a key frame
    "pos",               ///< original position in the file of the frame

    NULL
};

enum var_name {
    VAR_E,
    VAR_PHI,
    VAR_PI,

    VAR_TB,

    VAR_PTS,
    VAR_START_PTS,
    VAR_PREV_PTS,
    VAR_PREV_SELECTED_PTS,

    VAR_T,
    VAR_START_T,
    VAR_PREV_T,
    VAR_PREV_SELECTED_T,

    VAR_PICT_TYPE,
    VAR_PICT_TYPE_I,
    VAR_PICT_TYPE_P,
    VAR_PICT_TYPE_B,
    VAR_PICT_TYPE_S,
    VAR_PICT_TYPE_SI,
    VAR_PICT_TYPE_SP,
    VAR_PICT_TYPE_BI,

    VAR_INTERLACE_TYPE,
    VAR_INTERLACE_TYPE_P,
    VAR_INTERLACE_TYPE_T,
    VAR_INTERLACE_TYPE_B,

    VAR_N,
    VAR_SELECTED_N,
    VAR_PREV_SELECTED_N,

    VAR_KEY,

    VAR_VARS_NB
};

#define FIFO_SIZE 8

typedef struct SelectContext {
    const AVClass *class;
    char *expr_str;
    AVExpr *expr;
    double var_values[VAR_VARS_NB];
    double select;
    int cache_frames;
    AVFifoBuffer *pending_frames; ///< FIFO buffer of video frames
} SelectContext;

static av_cold int init(AVFilterContext *ctx)
{
    SelectContext *select = ctx->priv;
    int ret;

    if ((ret = av_expr_parse(&select->expr, select->expr_str,
                             var_names, NULL, NULL, NULL, NULL, 0, ctx)) < 0) {
        av_log(ctx, AV_LOG_ERROR, "Error while parsing expression '%s'\n",
               select->expr_str);
        return ret;
    }

    select->pending_frames = av_fifo_alloc(FIFO_SIZE*sizeof(AVFrame*));
    if (!select->pending_frames) {
        av_log(ctx, AV_LOG_ERROR, "Failed to allocate pending frames buffer.\n");
        return AVERROR(ENOMEM);
    }
    return 0;
}

#define INTERLACE_TYPE_P 0
#define INTERLACE_TYPE_T 1
#define INTERLACE_TYPE_B 2

static int config_input(AVFilterLink *inlink)
{
    SelectContext *select = inlink->dst->priv;

    select->var_values[VAR_E]   = M_E;
    select->var_values[VAR_PHI] = M_PHI;
    select->var_values[VAR_PI]  = M_PI;

    select->var_values[VAR_N]          = 0.0;
    select->var_values[VAR_SELECTED_N] = 0.0;

    select->var_values[VAR_TB] = av_q2d(inlink->time_base);

    select->var_values[VAR_PREV_PTS]          = NAN;
    select->var_values[VAR_PREV_SELECTED_PTS] = NAN;
    select->var_values[VAR_PREV_SELECTED_T]   = NAN;
    select->var_values[VAR_START_PTS]         = NAN;
    select->var_values[VAR_START_T]           = NAN;

    select->var_values[VAR_PICT_TYPE_I]  = AV_PICTURE_TYPE_I;
    select->var_values[VAR_PICT_TYPE_P]  = AV_PICTURE_TYPE_P;
    select->var_values[VAR_PICT_TYPE_B]  = AV_PICTURE_TYPE_B;
    select->var_values[VAR_PICT_TYPE_SI] = AV_PICTURE_TYPE_SI;
    select->var_values[VAR_PICT_TYPE_SP] = AV_PICTURE_TYPE_SP;

    select->var_values[VAR_INTERLACE_TYPE_P] = INTERLACE_TYPE_P;
    select->var_values[VAR_INTERLACE_TYPE_T] = INTERLACE_TYPE_T;
    select->var_values[VAR_INTERLACE_TYPE_B] = INTERLACE_TYPE_B;;

    return 0;
}

#define D2TS(d)  (isnan(d) ? AV_NOPTS_VALUE : (int64_t)(d))
#define TS2D(ts) ((ts) == AV_NOPTS_VALUE ? NAN : (double)(ts))

static int select_frame(AVFilterContext *ctx, AVFrame *frame)
{
    SelectContext *select = ctx->priv;
    AVFilterLink *inlink = ctx->inputs[0];
    double res;

    if (isnan(select->var_values[VAR_START_PTS]))
        select->var_values[VAR_START_PTS] = TS2D(frame->pts);
    if (isnan(select->var_values[VAR_START_T]))
        select->var_values[VAR_START_T] = TS2D(frame->pts) * av_q2d(inlink->time_base);

    select->var_values[VAR_PTS] = TS2D(frame->pts);
    select->var_values[VAR_T  ] = TS2D(frame->pts) * av_q2d(inlink->time_base);
    select->var_values[VAR_PREV_PTS] = TS2D(frame->pts);

    select->var_values[VAR_INTERLACE_TYPE] =
        !frame->interlaced_frame     ? INTERLACE_TYPE_P :
        frame->top_field_first ? INTERLACE_TYPE_T : INTERLACE_TYPE_B;
    select->var_values[VAR_PICT_TYPE] = frame->pict_type;

    res = av_expr_eval(select->expr, select->var_values, NULL);

    select->var_values[VAR_N] += 1.0;

    if (res) {
        select->var_values[VAR_PREV_SELECTED_N]   = select->var_values[VAR_N];
        select->var_values[VAR_PREV_SELECTED_PTS] = select->var_values[VAR_PTS];
        select->var_values[VAR_PREV_SELECTED_T]   = select->var_values[VAR_T];
        select->var_values[VAR_SELECTED_N] += 1.0;
    }
    return res;
}

static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
{
    SelectContext *select = inlink->dst->priv;

    select->select = select_frame(inlink->dst, frame);
    if (select->select) {
        /* frame was requested through poll_frame */
        if (select->cache_frames) {
            if (!av_fifo_space(select->pending_frames)) {
                av_log(inlink->dst, AV_LOG_ERROR,
                       "Buffering limit reached, cannot cache more frames\n");
                av_frame_free(&frame);
            } else
                av_fifo_generic_write(select->pending_frames, &frame,
                                      sizeof(frame), NULL);
            return 0;
        }
        return ff_filter_frame(inlink->dst->outputs[0], frame);
    }

    av_frame_free(&frame);
    return 0;
}

static int request_frame(AVFilterLink *outlink)
{
    AVFilterContext *ctx = outlink->src;
    SelectContext *select = ctx->priv;
    AVFilterLink *inlink = outlink->src->inputs[0];
    select->select = 0;

    if (av_fifo_size(select->pending_frames)) {
        AVFrame *frame;

        av_fifo_generic_read(select->pending_frames, &frame, sizeof(frame), NULL);
        return ff_filter_frame(outlink, frame);
    }

    while (!select->select) {
        int ret = ff_request_frame(inlink);
        if (ret < 0)
            return ret;
    }

    return 0;
}

static int poll_frame(AVFilterLink *outlink)
{
    SelectContext *select = outlink->src->priv;
    AVFilterLink *inlink = outlink->src->inputs[0];
    int count, ret;

    if (!av_fifo_size(select->pending_frames)) {
        if ((count = ff_poll_frame(inlink)) <= 0)
            return count;
        /* request frame from input, and apply select condition to it */
        select->cache_frames = 1;
        while (count-- && av_fifo_space(select->pending_frames)) {
            ret = ff_request_frame(inlink);
            if (ret < 0)
                break;
        }
        select->cache_frames = 0;
    }

    return av_fifo_size(select->pending_frames)/sizeof(AVFrame*);
}

static av_cold void uninit(AVFilterContext *ctx)
{
    SelectContext *select = ctx->priv;
    AVFrame *frame;

    av_expr_free(select->expr);
    select->expr = NULL;

    while (select->pending_frames &&
           av_fifo_generic_read(select->pending_frames, &frame, sizeof(frame), NULL) == sizeof(frame))
        av_frame_free(&frame);
    av_fifo_free(select->pending_frames);
    select->pending_frames = NULL;
}

#define OFFSET(x) offsetof(SelectContext, x)
#define FLAGS AV_OPT_FLAG_VIDEO_PARAM
static const AVOption options[] = {
    { "expr", "An expression to use for selecting frames", OFFSET(expr_str), AV_OPT_TYPE_STRING, { .str = "1" }, .flags = FLAGS },
    { NULL },
};

static const AVClass select_class = {
    .class_name = "select",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

static const AVFilterPad avfilter_vf_select_inputs[] = {
    {
        .name             = "default",
        .type             = AVMEDIA_TYPE_VIDEO,
        .get_video_buffer = ff_null_get_video_buffer,
        .config_props     = config_input,
        .filter_frame     = filter_frame,
    },
    { NULL }
};

static const AVFilterPad avfilter_vf_select_outputs[] = {
    {
        .name          = "default",
        .type          = AVMEDIA_TYPE_VIDEO,
        .poll_frame    = poll_frame,
        .request_frame = request_frame,
    },
    { NULL }
};

AVFilter ff_vf_select = {
    .name      = "select",
    .description = NULL_IF_CONFIG_SMALL("Select frames to pass in output."),
    .init      = init,
    .uninit    = uninit,

    .priv_size = sizeof(SelectContext),
    .priv_class = &select_class,

    .inputs    = avfilter_vf_select_inputs,
    .outputs   = avfilter_vf_select_outputs,
};