FFmpeg/libavfilter/vf_overlay.c

/*
 * Copyright (c) 2010 Stefano Sabatini
 * Copyright (c) 2010 Baptiste Coudurier
 * Copyright (c) 2007 Bobby Bingham
 *
 * 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
 */

/**
 * @file
 * overlay one video on top of another
 */

/* #define DEBUG */

#include "avfilter.h"
#include "formats.h"
#include "libavutil/common.h"
#include "libavutil/eval.h"
#include "libavutil/avstring.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
#include "libavutil/imgutils.h"
#include "libavutil/mathematics.h"
#include "libavutil/timestamp.h"
#include "internal.h"
#include "bufferqueue.h"
#include "drawutils.h"
#include "video.h"

static const char *const var_names[] = {
    "main_w",    "W", ///< width  of the main    video
    "main_h",    "H", ///< height of the main    video
    "overlay_w", "w", ///< width  of the overlay video
    "overlay_h", "h", ///< height of the overlay video
    "hsub",
    "vsub",
    "x",
    "y",
    "n",            ///< number of frame
    "pos",          ///< position in the file
    "t",            ///< timestamp expressed in seconds
    NULL
};

enum var_name {
    VAR_MAIN_W,    VAR_MW,
    VAR_MAIN_H,    VAR_MH,
    VAR_OVERLAY_W, VAR_OW,
    VAR_OVERLAY_H, VAR_OH,
    VAR_HSUB,
    VAR_VSUB,
    VAR_X,
    VAR_Y,
    VAR_N,
    VAR_POS,
    VAR_T,
    VAR_VARS_NB
};

#define MAIN    0
#define OVERLAY 1

#define R 0
#define G 1
#define B 2
#define A 3

#define Y 0
#define U 1
#define V 2

typedef struct {
    const AVClass *class;
    int x, y;                   ///< position of overlayed picture

    int allow_packed_rgb;
    uint8_t frame_requested;
    uint8_t overlay_eof;
    uint8_t main_is_packed_rgb;
    uint8_t main_rgba_map[4];
    uint8_t main_has_alpha;
    uint8_t overlay_is_packed_rgb;
    uint8_t overlay_rgba_map[4];
    uint8_t overlay_has_alpha;
    enum OverlayFormat { OVERLAY_FORMAT_YUV420, OVERLAY_FORMAT_YUV444, OVERLAY_FORMAT_RGB, OVERLAY_FORMAT_NB} format;
    enum EvalMode { EVAL_MODE_INIT, EVAL_MODE_FRAME, EVAL_MODE_NB } eval_mode;

    AVFrame *overpicref;
    struct FFBufQueue queue_main;
    struct FFBufQueue queue_over;

    int main_pix_step[4];       ///< steps per pixel for each plane of the main output
    int overlay_pix_step[4];    ///< steps per pixel for each plane of the overlay
    int hsub, vsub;             ///< chroma subsampling values
    int shortest;               ///< terminate stream when the shortest input terminates

    double var_values[VAR_VARS_NB];
    char *x_expr, *y_expr;
    AVExpr *x_pexpr, *y_pexpr;
} OverlayContext;

#define OFFSET(x) offsetof(OverlayContext, x)
#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM

static const AVOption overlay_options[] = {
    { "x", "set the x expression", OFFSET(x_expr), AV_OPT_TYPE_STRING, {.str = "0"}, CHAR_MIN, CHAR_MAX, FLAGS },
    { "y", "set the y expression", OFFSET(y_expr), AV_OPT_TYPE_STRING, {.str = "0"}, CHAR_MIN, CHAR_MAX, FLAGS },

    { "eval", "specify when to evaluate expressions", OFFSET(eval_mode), AV_OPT_TYPE_INT, {.i64 = EVAL_MODE_FRAME}, 0, EVAL_MODE_NB-1, FLAGS, "eval" },
    { "init",  "eval expressions once during initialization", 0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_INIT}, .flags = FLAGS, .unit = "eval" },
    { "frame", "eval expressions per-frame",   0, AV_OPT_TYPE_CONST, {.i64=EVAL_MODE_FRAME}, .flags = FLAGS, .unit = "eval" },

    { "rgb", "force packed RGB in input and output (deprecated)", OFFSET(allow_packed_rgb), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS },
    { "shortest", "force termination when the shortest input terminates", OFFSET(shortest), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, FLAGS },

    { "format", "set output format", OFFSET(format), AV_OPT_TYPE_INT, {.i64=OVERLAY_FORMAT_YUV420}, 0, OVERLAY_FORMAT_NB-1, FLAGS, "format" },
    { "yuv420", "", 0, AV_OPT_TYPE_CONST, {.i64=OVERLAY_FORMAT_YUV420}, .flags = FLAGS, .unit = "format" },
    { "yuv444", "", 0, AV_OPT_TYPE_CONST, {.i64=OVERLAY_FORMAT_YUV444}, .flags = FLAGS, .unit = "format" },
    { "rgb",    "", 0, AV_OPT_TYPE_CONST, {.i64=OVERLAY_FORMAT_RGB},    .flags = FLAGS, .unit = "format" },

    { NULL }
};

AVFILTER_DEFINE_CLASS(overlay);

static av_cold int init(AVFilterContext *ctx, const char *args)
{
    OverlayContext *over = ctx->priv;

    if (over->allow_packed_rgb) {
        av_log(ctx, AV_LOG_WARNING,
               "The rgb option is deprecated and is overriding the format option, use format instead\n");
        over->format = OVERLAY_FORMAT_RGB;
    }
    return 0;
}

static av_cold void uninit(AVFilterContext *ctx)
{
    OverlayContext *over = ctx->priv;

    av_frame_free(&over->overpicref);
    ff_bufqueue_discard_all(&over->queue_main);
    ff_bufqueue_discard_all(&over->queue_over);
    av_expr_free(over->x_pexpr); over->x_pexpr = NULL;
    av_expr_free(over->y_pexpr); over->y_pexpr = NULL;
}

static int query_formats(AVFilterContext *ctx)
{
    OverlayContext *over = ctx->priv;

    /* overlay formats contains alpha, for avoiding conversion with alpha information loss */
    static const enum AVPixelFormat main_pix_fmts_yuv420[] = {
        AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUVA420P, AV_PIX_FMT_NONE
    };
    static const enum AVPixelFormat overlay_pix_fmts_yuv420[] = {
        AV_PIX_FMT_YUVA420P, AV_PIX_FMT_NONE
    };

    static const enum AVPixelFormat main_pix_fmts_yuv444[] = {
        AV_PIX_FMT_YUV444P, AV_PIX_FMT_YUVA444P, AV_PIX_FMT_NONE
    };
    static const enum AVPixelFormat overlay_pix_fmts_yuv444[] = {
        AV_PIX_FMT_YUVA444P, AV_PIX_FMT_NONE
    };

    static const enum AVPixelFormat main_pix_fmts_rgb[] = {
        AV_PIX_FMT_ARGB,  AV_PIX_FMT_RGBA,
        AV_PIX_FMT_ABGR,  AV_PIX_FMT_BGRA,
        AV_PIX_FMT_RGB24, AV_PIX_FMT_BGR24,
        AV_PIX_FMT_NONE
    };
    static const enum AVPixelFormat overlay_pix_fmts_rgb[] = {
        AV_PIX_FMT_ARGB,  AV_PIX_FMT_RGBA,
        AV_PIX_FMT_ABGR,  AV_PIX_FMT_BGRA,
        AV_PIX_FMT_NONE
    };

    AVFilterFormats *main_formats;
    AVFilterFormats *overlay_formats;

    switch (over->format) {
    case OVERLAY_FORMAT_YUV420:
        main_formats    = ff_make_format_list(main_pix_fmts_yuv420);
        overlay_formats = ff_make_format_list(overlay_pix_fmts_yuv420);
        break;
    case OVERLAY_FORMAT_YUV444:
        main_formats    = ff_make_format_list(main_pix_fmts_yuv444);
        overlay_formats = ff_make_format_list(overlay_pix_fmts_yuv444);
        break;
    case OVERLAY_FORMAT_RGB:
        main_formats    = ff_make_format_list(main_pix_fmts_rgb);
        overlay_formats = ff_make_format_list(overlay_pix_fmts_rgb);
        break;
    default:
        av_assert0(0);
    }

    ff_formats_ref(main_formats,    &ctx->inputs [MAIN   ]->out_formats);
    ff_formats_ref(overlay_formats, &ctx->inputs [OVERLAY]->out_formats);
    ff_formats_ref(main_formats,    &ctx->outputs[MAIN   ]->in_formats );

    return 0;
}

static const enum AVPixelFormat alpha_pix_fmts[] = {
    AV_PIX_FMT_YUVA420P, AV_PIX_FMT_YUVA444P,
    AV_PIX_FMT_ARGB, AV_PIX_FMT_ABGR, AV_PIX_FMT_RGBA,
    AV_PIX_FMT_BGRA, AV_PIX_FMT_NONE
};

static int config_input_main(AVFilterLink *inlink)
{
    OverlayContext *over = inlink->dst->priv;
    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(inlink->format);

    av_image_fill_max_pixsteps(over->main_pix_step,    NULL, pix_desc);

    over->hsub = pix_desc->log2_chroma_w;
    over->vsub = pix_desc->log2_chroma_h;

    over->main_is_packed_rgb =
        ff_fill_rgba_map(over->main_rgba_map, inlink->format) >= 0;
    over->main_has_alpha = ff_fmt_is_in(inlink->format, alpha_pix_fmts);
    return 0;
}

static inline int normalize_xy(double d, int chroma_sub)
{
    if (isnan(d))
        return INT_MAX;
    return (int)d & ~((1 << chroma_sub) - 1);
}

static void eval_expr(AVFilterContext *ctx)
{
    OverlayContext  *over = ctx->priv;

    over->var_values[VAR_X] = av_expr_eval(over->x_pexpr, over->var_values, NULL);
    over->var_values[VAR_Y] = av_expr_eval(over->y_pexpr, over->var_values, NULL);
    over->var_values[VAR_X] = av_expr_eval(over->x_pexpr, over->var_values, NULL);
    over->x = normalize_xy(over->var_values[VAR_X], over->hsub);
    over->y = normalize_xy(over->var_values[VAR_Y], over->vsub);
}

static int config_input_overlay(AVFilterLink *inlink)
{
    AVFilterContext *ctx  = inlink->dst;
    OverlayContext  *over = inlink->dst->priv;
    char *expr;
    int ret;
    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(inlink->format);

    av_image_fill_max_pixsteps(over->overlay_pix_step, NULL, pix_desc);

    /* Finish the configuration by evaluating the expressions
       now when both inputs are configured. */
    over->var_values[VAR_MAIN_W   ] = over->var_values[VAR_MW] = ctx->inputs[MAIN   ]->w;
    over->var_values[VAR_MAIN_H   ] = over->var_values[VAR_MH] = ctx->inputs[MAIN   ]->h;
    over->var_values[VAR_OVERLAY_W] = over->var_values[VAR_OW] = ctx->inputs[OVERLAY]->w;
    over->var_values[VAR_OVERLAY_H] = over->var_values[VAR_OH] = ctx->inputs[OVERLAY]->h;
    over->var_values[VAR_HSUB]  = 1<<pix_desc->log2_chroma_w;
    over->var_values[VAR_VSUB]  = 1<<pix_desc->log2_chroma_h;
    over->var_values[VAR_X]     = NAN;
    over->var_values[VAR_Y]     = NAN;
    over->var_values[VAR_N]     = 0;
    over->var_values[VAR_T]     = NAN;
    over->var_values[VAR_POS]   = NAN;

    expr = over->x_expr;
    if ((ret = av_expr_parse(&over->x_pexpr, expr, var_names,
                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
        goto fail;
    expr = over->y_expr;
    if ((ret = av_expr_parse(&over->y_pexpr, expr, var_names,
                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
        goto fail;

    over->overlay_is_packed_rgb =
        ff_fill_rgba_map(over->overlay_rgba_map, inlink->format) >= 0;
    over->overlay_has_alpha = ff_fmt_is_in(inlink->format, alpha_pix_fmts);

    if (over->eval_mode == EVAL_MODE_INIT) {
        eval_expr(ctx);
        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d\n",
               over->var_values[VAR_X], over->x,
               over->var_values[VAR_Y], over->y);
    }

    av_log(ctx, AV_LOG_VERBOSE,
           "main w:%d h:%d fmt:%s overlay w:%d h:%d fmt:%s\n",
           ctx->inputs[MAIN]->w, ctx->inputs[MAIN]->h,
           av_get_pix_fmt_name(ctx->inputs[MAIN]->format),
           ctx->inputs[OVERLAY]->w, ctx->inputs[OVERLAY]->h,
           av_get_pix_fmt_name(ctx->inputs[OVERLAY]->format));
    return 0;

fail:
    av_log(NULL, AV_LOG_ERROR,
           "Error when parsing the expression '%s'\n", expr);
    return ret;
}

static int config_output(AVFilterLink *outlink)
{
    AVFilterContext *ctx = outlink->src;

    outlink->w = ctx->inputs[MAIN]->w;
    outlink->h = ctx->inputs[MAIN]->h;
    outlink->time_base = ctx->inputs[MAIN]->time_base;

    return 0;
}

// divide by 255 and round to nearest
// apply a fast variant: (X+127)/255 = ((X+127)*257+257)>>16 = ((X+128)*257)>>16
#define FAST_DIV255(x) ((((x) + 128) * 257) >> 16)

// calculate the unpremultiplied alpha, applying the general equation:
// alpha = alpha_overlay / ( (alpha_main + alpha_overlay) - (alpha_main * alpha_overlay) )
// (((x) << 16) - ((x) << 9) + (x)) is a faster version of: 255 * 255 * x
// ((((x) + (y)) << 8) - ((x) + (y)) - (y) * (x)) is a faster version of: 255 * (x + y)
#define UNPREMULTIPLY_ALPHA(x, y) ((((x) << 16) - ((x) << 9) + (x)) / ((((x) + (y)) << 8) - ((x) + (y)) - (y) * (x)))

/**
 * Blend image in src to destination buffer dst at position (x, y).
 */
static void blend_image(AVFilterContext *ctx,
                        AVFrame *dst, AVFrame *src,
                        int x, int y)
{
    OverlayContext *over = ctx->priv;
    int i, imax, j, jmax, k, kmax;
    const int src_w = src->width;
    const int src_h = src->height;
    const int dst_w = dst->width;
    const int dst_h = dst->height;

    if (x >= dst_w || x+dst_w  < 0 ||
        y >= dst_h || y+dst_h < 0)
        return; /* no intersection */

    if (over->main_is_packed_rgb) {
        uint8_t alpha;          ///< the amount of overlay to blend on to main
        const int dr = over->main_rgba_map[R];
        const int dg = over->main_rgba_map[G];
        const int db = over->main_rgba_map[B];
        const int da = over->main_rgba_map[A];
        const int dstep = over->main_pix_step[0];
        const int sr = over->overlay_rgba_map[R];
        const int sg = over->overlay_rgba_map[G];
        const int sb = over->overlay_rgba_map[B];
        const int sa = over->overlay_rgba_map[A];
        const int sstep = over->overlay_pix_step[0];
        const int main_has_alpha = over->main_has_alpha;
        uint8_t *s, *sp, *d, *dp;

        i = FFMAX(-y, 0);
        sp = src->data[0] + i     * src->linesize[0];
        dp = dst->data[0] + (y+i) * dst->linesize[0];

        for (imax = FFMIN(-y + dst_h, src_h); i < imax; i++) {
            j = FFMAX(-x, 0);
            s = sp + j     * sstep;
            d = dp + (x+j) * dstep;

            for (jmax = FFMIN(-x + dst_w, src_w); j < jmax; j++) {
                alpha = s[sa];

                // if the main channel has an alpha channel, alpha has to be calculated
                // to create an un-premultiplied (straight) alpha value
                if (main_has_alpha && alpha != 0 && alpha != 255) {
                    uint8_t alpha_d = d[da];
                    alpha = UNPREMULTIPLY_ALPHA(alpha, alpha_d);
                }

                switch (alpha) {
                case 0:
                    break;
                case 255:
                    d[dr] = s[sr];
                    d[dg] = s[sg];
                    d[db] = s[sb];
                    break;
                default:
                    // main_value = main_value * (1 - alpha) + overlay_value * alpha
                    // since alpha is in the range 0-255, the result must divided by 255
                    d[dr] = FAST_DIV255(d[dr] * (255 - alpha) + s[sr] * alpha);
                    d[dg] = FAST_DIV255(d[dg] * (255 - alpha) + s[sg] * alpha);
                    d[db] = FAST_DIV255(d[db] * (255 - alpha) + s[sb] * alpha);
                }
                if (main_has_alpha) {
                    switch (alpha) {
                    case 0:
                        break;
                    case 255:
                        d[da] = s[sa];
                        break;
                    default:
                        // apply alpha compositing: main_alpha += (1-main_alpha) * overlay_alpha
                        d[da] += FAST_DIV255((255 - d[da]) * s[sa]);
                    }
                }
                d += dstep;
                s += sstep;
            }
            dp += dst->linesize[0];
            sp += src->linesize[0];
        }
    } else {
        const int main_has_alpha = over->main_has_alpha;
        if (main_has_alpha) {
            uint8_t alpha;          ///< the amount of overlay to blend on to main
            uint8_t *s, *sa, *d, *da;

            i = FFMAX(-y, 0);
            sa = src->data[3] + i     * src->linesize[3];
            da = dst->data[3] + (y+i) * dst->linesize[3];

            for (imax = FFMIN(-y + dst_h, src_h); i < imax; i++) {
                j = FFMAX(-x, 0);
                s = sa + j;
                d = da + x+j;

                for (jmax = FFMIN(-x + dst_w, src_w); j < jmax; j++) {
                    alpha = *s;
                    if (alpha != 0 && alpha != 255) {
                        uint8_t alpha_d = *d;
                        alpha = UNPREMULTIPLY_ALPHA(alpha, alpha_d);
                    }
                    switch (alpha) {
                    case 0:
                        break;
                    case 255:
                        *d = *s;
                        break;
                    default:
                        // apply alpha compositing: main_alpha += (1-main_alpha) * overlay_alpha
                        *d += FAST_DIV255((255 - *d) * *s);
                    }
                    d += 1;
                    s += 1;
                }
                da += dst->linesize[3];
                sa += src->linesize[3];
            }
        }
        for (i = 0; i < 3; i++) {
            int hsub = i ? over->hsub : 0;
            int vsub = i ? over->vsub : 0;
            int src_wp = FFALIGN(src_w, 1<<hsub) >> hsub;
            int src_hp = FFALIGN(src_h, 1<<vsub) >> vsub;
            int dst_wp = FFALIGN(dst_w, 1<<hsub) >> hsub;
            int dst_hp = FFALIGN(dst_h, 1<<vsub) >> vsub;
            int yp = y>>vsub;
            int xp = x>>hsub;
            uint8_t *s, *sp, *d, *dp, *a, *ap;

            j = FFMAX(-yp, 0);
            sp = src->data[i] + j         * src->linesize[i];
            dp = dst->data[i] + (yp+j)    * dst->linesize[i];
            ap = src->data[3] + (j<<vsub) * src->linesize[3];

            for (jmax = FFMIN(-yp + dst_hp, src_hp); j < jmax; j++) {
                k = FFMAX(-xp, 0);
                d = dp + xp+k;
                s = sp + k;
                a = ap + (k<<hsub);

                for (kmax = FFMIN(-xp + dst_wp, src_wp); k < kmax; k++) {
                    int alpha_v, alpha_h, alpha;

                    // average alpha for color components, improve quality
                    if (hsub && vsub && j+1 < src_hp && k+1 < src_wp) {
                        alpha = (a[0] + a[src->linesize[3]] +
                                 a[1] + a[src->linesize[3]+1]) >> 2;
                    } else if (hsub || vsub) {
                        alpha_h = hsub && k+1 < src_wp ?
                            (a[0] + a[1]) >> 1 : a[0];
                        alpha_v = vsub && j+1 < src_hp ?
                            (a[0] + a[src->linesize[3]]) >> 1 : a[0];
                        alpha = (alpha_v + alpha_h) >> 1;
                    } else
                        alpha = a[0];
                    // if the main channel has an alpha channel, alpha has to be calculated
                    // to create an un-premultiplied (straight) alpha value
                    if (main_has_alpha && alpha != 0 && alpha != 255) {
                        // average alpha for color components, improve quality
                        uint8_t alpha_d;
                        if (hsub && vsub && j+1 < src_hp && k+1 < src_wp) {
                            alpha_d = (d[0] + d[src->linesize[3]] +
                                       d[1] + d[src->linesize[3]+1]) >> 2;
                        } else if (hsub || vsub) {
                            alpha_h = hsub && k+1 < src_wp ?
                                (d[0] + d[1]) >> 1 : d[0];
                            alpha_v = vsub && j+1 < src_hp ?
                                (d[0] + d[src->linesize[3]]) >> 1 : d[0];
                            alpha_d = (alpha_v + alpha_h) >> 1;
                        } else
                            alpha_d = d[0];
                        alpha = UNPREMULTIPLY_ALPHA(alpha, alpha_d);
                    }
                    *d = FAST_DIV255(*d * (255 - alpha) + *s * alpha);
                    s++;
                    d++;
                    a += 1 << hsub;
                }
                dp += dst->linesize[i];
                sp += src->linesize[i];
                ap += (1 << vsub) * src->linesize[3];
            }
        }
    }
}

static int try_filter_frame(AVFilterContext *ctx, AVFrame *mainpic)
{
    OverlayContext *over = ctx->priv;
    AVFilterLink *inlink = ctx->inputs[0];
    AVFrame *next_overpic;
    int ret;

    /* Discard obsolete overlay frames: if there is a next overlay frame with pts
     * before the main frame, we can drop the current overlay. */
    while (1) {
        next_overpic = ff_bufqueue_peek(&over->queue_over, 0);
        if (!next_overpic || av_compare_ts(next_overpic->pts, ctx->inputs[OVERLAY]->time_base,
                                           mainpic->pts     , ctx->inputs[MAIN]->time_base) > 0)
            break;
        ff_bufqueue_get(&over->queue_over);
        av_frame_free(&over->overpicref);
        over->overpicref = next_overpic;
    }

    /* If there is no next frame and no EOF and the overlay frame is before
     * the main frame, we can not know yet if it will be superseded. */
    if (!over->queue_over.available && !over->overlay_eof &&
        (!over->overpicref || av_compare_ts(over->overpicref->pts, ctx->inputs[OVERLAY]->time_base,
                                            mainpic->pts         , ctx->inputs[MAIN]->time_base) < 0))
        return AVERROR(EAGAIN);

    /* At this point, we know that the current overlay frame extends to the
     * time of the main frame. */
    av_dlog(ctx, "main_pts:%s main_pts_time:%s",
            av_ts2str(mainpic->pts), av_ts2timestr(mainpic->pts, &ctx->inputs[MAIN]->time_base));
    if (over->overpicref)
        av_dlog(ctx, " over_pts:%s over_pts_time:%s",
                av_ts2str(over->overpicref->pts), av_ts2timestr(over->overpicref->pts, &ctx->inputs[OVERLAY]->time_base));
    av_dlog(ctx, "\n");

    if (over->overpicref) {
        if (over->eval_mode == EVAL_MODE_FRAME) {
            int64_t pos = av_frame_get_pkt_pos(mainpic);

            over->var_values[VAR_T] = mainpic->pts == AV_NOPTS_VALUE ?
                NAN : mainpic->pts * av_q2d(inlink->time_base);
            over->var_values[VAR_POS] = pos == -1 ? NAN : pos;

            eval_expr(ctx);
            av_log(ctx, AV_LOG_DEBUG, "n:%f t:%f pos:%f x:%f xi:%d y:%f yi:%d\n",
                   over->var_values[VAR_N], over->var_values[VAR_T], over->var_values[VAR_POS],
                   over->var_values[VAR_X], over->x,
                   over->var_values[VAR_Y], over->y);
        }
        blend_image(ctx, mainpic, over->overpicref, over->x, over->y);

        over->var_values[VAR_N] += 1.0;
    }
    ret = ff_filter_frame(ctx->outputs[0], mainpic);
    av_assert1(ret != AVERROR(EAGAIN));
    over->frame_requested = 0;
    return ret;
}

static int try_filter_next_frame(AVFilterContext *ctx)
{
    OverlayContext *over = ctx->priv;
    AVFrame *next_mainpic = ff_bufqueue_peek(&over->queue_main, 0);
    int ret;

    if (!next_mainpic)
        return AVERROR(EAGAIN);
    if ((ret = try_filter_frame(ctx, next_mainpic)) == AVERROR(EAGAIN))
        return ret;
    ff_bufqueue_get(&over->queue_main);
    return ret;
}

static int flush_frames(AVFilterContext *ctx)
{
    int ret;

    while (!(ret = try_filter_next_frame(ctx)));
    return ret == AVERROR(EAGAIN) ? 0 : ret;
}

static int filter_frame_main(AVFilterLink *inlink, AVFrame *inpicref)
{
    AVFilterContext *ctx = inlink->dst;
    OverlayContext *over = ctx->priv;
    int ret;

    if ((ret = flush_frames(ctx)) < 0)
        return ret;
    if ((ret = try_filter_frame(ctx, inpicref)) < 0) {
        if (ret != AVERROR(EAGAIN))
            return ret;
        ff_bufqueue_add(ctx, &over->queue_main, inpicref);
    }

    if (!over->overpicref)
        return 0;
    flush_frames(ctx);

    return 0;
}

static int filter_frame_over(AVFilterLink *inlink, AVFrame *inpicref)
{
    AVFilterContext *ctx = inlink->dst;
    OverlayContext *over = ctx->priv;
    int ret;

    if ((ret = flush_frames(ctx)) < 0)
        return ret;
    ff_bufqueue_add(ctx, &over->queue_over, inpicref);
    ret = try_filter_next_frame(ctx);
    return ret == AVERROR(EAGAIN) ? 0 : ret;
}

static int request_frame(AVFilterLink *outlink)
{
    AVFilterContext *ctx = outlink->src;
    OverlayContext *over = ctx->priv;
    int input, ret;

    if (!try_filter_next_frame(ctx))
        return 0;
    over->frame_requested = 1;
    while (over->frame_requested) {
        /* TODO if we had a frame duration, we could guess more accurately */
        input = !over->overlay_eof && (over->queue_main.available ||
                                       over->queue_over.available < 2) ?
                OVERLAY : MAIN;
        ret = ff_request_frame(ctx->inputs[input]);
        /* EOF on main is reported immediately */
        if (ret == AVERROR_EOF && input == OVERLAY) {
            over->overlay_eof = 1;
            if (over->shortest)
                return ret;
            if ((ret = try_filter_next_frame(ctx)) != AVERROR(EAGAIN))
                return ret;
            ret = 0; /* continue requesting frames on main */
        }
        if (ret < 0)
            return ret;
    }
    return 0;
}

static const AVFilterPad avfilter_vf_overlay_inputs[] = {
    {
        .name         = "main",
        .type         = AVMEDIA_TYPE_VIDEO,
        .get_video_buffer = ff_null_get_video_buffer,
        .config_props = config_input_main,
        .filter_frame = filter_frame_main,
        .needs_writable = 1,
    },
    {
        .name         = "overlay",
        .type         = AVMEDIA_TYPE_VIDEO,
        .config_props = config_input_overlay,
        .filter_frame = filter_frame_over,
    },
    { NULL }
};

static const AVFilterPad avfilter_vf_overlay_outputs[] = {
    {
        .name          = "default",
        .type          = AVMEDIA_TYPE_VIDEO,
        .config_props  = config_output,
        .request_frame = request_frame,
    },
    { NULL }
};

static const char *const shorthand[] = { "x", "y", NULL };

AVFilter avfilter_vf_overlay = {
    .name      = "overlay",
    .description = NULL_IF_CONFIG_SMALL("Overlay a video source on top of the input."),

    .init      = init,
    .uninit    = uninit,

    .priv_size = sizeof(OverlayContext),

    .query_formats = query_formats,

    .inputs    = avfilter_vf_overlay_inputs,
    .outputs   = avfilter_vf_overlay_outputs,
    .priv_class = &overlay_class,
    .shorthand  = shorthand,
};