libavfilter/vf_overlay.c

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/*
 * 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
 */

/* #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", 
    "main_h",    "H", 
    "overlay_w", "w", 
    "overlay_h", "h", 
    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_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;                   

    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;

    AVFilterBufferRef *overpicref;
    struct FFBufQueue queue_main;
    struct FFBufQueue queue_over;

    int main_pix_step[4];       
    int overlay_pix_step[4];    
    int hsub, vsub;             

    char *x_expr, *y_expr;
} 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 },
    {"rgb", "force packed RGB in input and output", OFFSET(allow_packed_rgb), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS },
    {NULL},
};

AVFILTER_DEFINE_CLASS(overlay);

static av_cold int init(AVFilterContext *ctx, const char *args)
{
    OverlayContext *over = ctx->priv;
    char *args1 = av_strdup(args);
    char *expr, *bufptr = NULL;
    int ret = 0;

    over->class = &overlay_class;
    av_opt_set_defaults(over);

    if (expr = av_strtok(args1, ":", &bufptr)) {
        av_free(over->x_expr);
        if (!(over->x_expr = av_strdup(expr))) {
            ret = AVERROR(ENOMEM);
            goto end;
        }
    }
    if (expr = av_strtok(NULL, ":", &bufptr)) {
        av_free(over->y_expr);
        if (!(over->y_expr = av_strdup(expr))) {
            ret = AVERROR(ENOMEM);
            goto end;
        }
    }

    if (bufptr && (ret = av_set_options_string(over, bufptr, "=", ":")) < 0)
        goto end;

end:
    av_free(args1);
    return ret;
}

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

    av_freep(&over->x_expr);
    av_freep(&over->y_expr);

    avfilter_unref_bufferp(&over->overpicref);
    ff_bufqueue_discard_all(&over->queue_main);
    ff_bufqueue_discard_all(&over->queue_over);
}

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

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

    if (over->allow_packed_rgb) {
        main_formats    = ff_make_format_list(main_pix_fmts_rgb);
        overlay_formats = ff_make_format_list(overlay_pix_fmts_rgb);
    } else {
        main_formats    = ff_make_format_list(main_pix_fmts_yuv);
        overlay_formats = ff_make_format_list(overlay_pix_fmts_yuv);
    }

    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_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 int config_input_overlay(AVFilterLink *inlink)
{
    AVFilterContext *ctx  = inlink->dst;
    OverlayContext  *over = inlink->dst->priv;
    char *expr;
    double var_values[VAR_VARS_NB], res;
    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. */
    var_values[VAR_MAIN_W   ] = var_values[VAR_MW] = ctx->inputs[MAIN   ]->w;
    var_values[VAR_MAIN_H   ] = var_values[VAR_MH] = ctx->inputs[MAIN   ]->h;
    var_values[VAR_OVERLAY_W] = var_values[VAR_OW] = ctx->inputs[OVERLAY]->w;
    var_values[VAR_OVERLAY_H] = var_values[VAR_OH] = ctx->inputs[OVERLAY]->h;

    if ((ret = av_expr_parse_and_eval(&res, (expr = over->x_expr), var_names, var_values,
                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
        goto fail;
    over->x = res;
    if ((ret = av_expr_parse_and_eval(&res, (expr = over->y_expr), var_names, var_values,
                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)))
        goto fail;
    over->y = res;
    /* x may depend on y */
    if ((ret = av_expr_parse_and_eval(&res, (expr = over->x_expr), var_names, var_values,
                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
        goto fail;
    over->x = res;

    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);

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

    if (over->x < 0 || over->y < 0 ||
        over->x + var_values[VAR_OVERLAY_W] > var_values[VAR_MAIN_W] ||
        over->y + var_values[VAR_OVERLAY_H] > var_values[VAR_MAIN_H]) {
        av_log(ctx, AV_LOG_ERROR,
               "Overlay area (%d,%d)<->(%d,%d) not within the main area (0,0)<->(%d,%d) or zero-sized\n",
               over->x, over->y,
               (int)(over->x + var_values[VAR_OVERLAY_W]),
               (int)(over->y + var_values[VAR_OVERLAY_H]),
               (int)var_values[VAR_MAIN_W], (int)var_values[VAR_MAIN_H]);
        return AVERROR(EINVAL);
    }
    return 0;

fail:
    av_log(NULL, AV_LOG_ERROR,
           "Error when evaluating 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)))

static void blend_slice(AVFilterContext *ctx,
                        AVFilterBufferRef *dst, AVFilterBufferRef *src,
                        int x, int y, int w, int h,
                        int slice_y, int slice_w, int slice_h)
{
    OverlayContext *over = ctx->priv;
    int i, j, k;
    int width, height;
    int overlay_end_y = y+h;
    int slice_end_y = slice_y+slice_h;
    int end_y, start_y;

    width = FFMIN(slice_w - x, w);
    end_y = FFMIN(slice_end_y, overlay_end_y);
    start_y = FFMAX(y, slice_y);
    height = end_y - start_y;

    if (over->main_is_packed_rgb) {
        uint8_t *dp = dst->data[0] + x * over->main_pix_step[0] +
                      start_y * dst->linesize[0];
        uint8_t *sp = src->data[0];
        uint8_t alpha;          
        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;
        if (slice_y > y)
            sp += (slice_y - y) * src->linesize[0];
        for (i = 0; i < height; i++) {
            uint8_t *d = dp, *s = sp;
            for (j = 0; j < width; 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 *da = dst->data[3] + x * over->main_pix_step[3] +
                          start_y * dst->linesize[3];
            uint8_t *sa = src->data[3];
            uint8_t alpha;          
            if (slice_y > y)
                sa += (slice_y - y) * src->linesize[3];
            for (i = 0; i < height; i++) {
                uint8_t *d = da, *s = sa;
                for (j = 0; j < width; 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;
            uint8_t *dp = dst->data[i] + (x >> hsub) +
                (start_y >> vsub) * dst->linesize[i];
            uint8_t *sp = src->data[i];
            uint8_t *ap = src->data[3];
            int wp = FFALIGN(width, 1<<hsub) >> hsub;
            int hp = FFALIGN(height, 1<<vsub) >> vsub;
            if (slice_y > y) {
                sp += ((slice_y - y) >> vsub) * src->linesize[i];
                ap += (slice_y - y) * src->linesize[3];
            }
            for (j = 0; j < hp; j++) {
                uint8_t *d = dp, *s = sp, *a = ap;
                for (k = 0; k < wp; k++) {
                    // average alpha for color components, improve quality
                    int alpha_v, alpha_h, alpha;
                    if (hsub && vsub && j+1 < hp && k+1 < 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 < wp ?
                            (a[0] + a[1]) >> 1 : a[0];
                        alpha_v = vsub && j+1 < 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 < hp && k+1 < 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 < wp ?
                                (d[0] + d[1]) >> 1 : d[0];
                            alpha_v = vsub && j+1 < 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_start_frame(AVFilterContext *ctx, AVFilterBufferRef *mainpic)
{
    OverlayContext *over = ctx->priv;
    AVFilterLink *outlink = ctx->outputs[0];
    AVFilterBufferRef *next_overpic, *outpicref;
    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);
        avfilter_unref_buffer(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. */
    outlink->out_buf = outpicref = avfilter_ref_buffer(mainpic, ~0);

    av_dlog(ctx, "main_pts:%s main_pts_time:%s",
            av_ts2str(outpicref->pts), av_ts2timestr(outpicref->pts, &outlink->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, &outlink->time_base));
    av_dlog(ctx, "\n");

    ret = ff_start_frame(ctx->outputs[0], avfilter_ref_buffer(outpicref, ~0));
    over->frame_requested = 0;
    return ret;
}

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

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

static int try_push_frame(AVFilterContext *ctx)
{
    OverlayContext *over = ctx->priv;
    AVFilterLink *outlink = ctx->outputs[0];
    AVFilterBufferRef *outpicref;
    int ret;

    if ((ret = try_start_next_frame(ctx)) < 0)
        return ret;
    outpicref = outlink->out_buf;
    if (over->overpicref)
        blend_slice(ctx, outpicref, over->overpicref, over->x, over->y,
                    over->overpicref->video->w, over->overpicref->video->h,
                    0, outpicref->video->w, outpicref->video->h);
    if ((ret = ff_draw_slice(outlink, 0, outpicref->video->h, +1)) < 0 ||
        (ret = ff_end_frame(outlink)) < 0)
        return ret;
    return 0;
}

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

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

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

    if ((ret = flush_frames(ctx)) < 0)
        return ret;
    if ((ret = try_start_frame(ctx, inpicref)) < 0) {
        if (ret != AVERROR(EAGAIN))
            return ret;
        ff_bufqueue_add(ctx, &over->queue_main, inpicref);
        av_assert1(inpicref == inlink->cur_buf);
        inlink->cur_buf = NULL;
    }
    return 0;
}

static int draw_slice_main(AVFilterLink *inlink, int y, int h, int slice_dir)
{
    AVFilterContext *ctx = inlink->dst;
    OverlayContext *over = ctx->priv;
    AVFilterLink *outlink = ctx->outputs[0];
    AVFilterBufferRef *outpicref = outlink->out_buf;

    if (!outpicref)
        return 0;
    if (over->overpicref &&
        y + h > over->y && y < over->y + over->overpicref->video->h) {
        blend_slice(ctx, outpicref, over->overpicref, over->x, over->y,
                    over->overpicref->video->w, over->overpicref->video->h,
                    y, outpicref->video->w, h);
    }
    return ff_draw_slice(outlink, y, h, slice_dir);
}

static int end_frame_main(AVFilterLink *inlink)
{
    AVFilterContext *ctx = inlink->dst;
    AVFilterLink *outlink = ctx->outputs[0];
    AVFilterBufferRef *outpicref = outlink->out_buf;
    flush_frames(ctx);

    if (!outpicref)
        return 0;
    return ff_end_frame(ctx->outputs[0]);
}

static int start_frame_over(AVFilterLink *inlink, AVFilterBufferRef *inpicref)
{
    return 0;
}

static int end_frame_over(AVFilterLink *inlink)
{
    AVFilterContext *ctx = inlink->dst;
    OverlayContext *over = ctx->priv;
    AVFilterBufferRef *inpicref = inlink->cur_buf;
    int ret;

    inlink->cur_buf = NULL;

    if ((ret = flush_frames(ctx)) < 0)
        return ret;
    ff_bufqueue_add(ctx, &over->queue_over, inpicref);
    ret = try_push_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_push_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 ((ret = try_start_next_frame(ctx)) != AVERROR(EAGAIN))
                return ret;
            ret = 0; /* continue requesting frames on main */
        }
        if (ret < 0)
            return ret;
    }
    return 0;
}

static int null_draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)
{
    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,
        .start_frame  = start_frame_main,
        .draw_slice   = draw_slice_main,
        .end_frame    = end_frame_main,
        .min_perms    = AV_PERM_READ | AV_PERM_WRITE | AV_PERM_PRESERVE,
    },
    {
        .name         = "overlay",
        .type         = AVMEDIA_TYPE_VIDEO,
        .config_props = config_input_overlay,
        .start_frame  = start_frame_over,
        .draw_slice   = null_draw_slice,
        .end_frame    = end_frame_over,
        .min_perms    = AV_PERM_READ | AV_PERM_PRESERVE,
    },
    { NULL }
};

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

---