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[FFmpeg-devel,v16,07/16] avfilter/overlaygraphicsubs: Add overlaygraphicsubs and graphicsub2video filters

Message ID DM8P223MB0365A4B21E7E3C4123FB004CBA629@DM8P223MB0365.NAMP223.PROD.OUTLOOK.COM
State Superseded, archived
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Series [FFmpeg-devel,v16,01/16] global: Prepare AVFrame for subtitle handling
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Soft Works Nov. 25, 2021, 5:53 p.m. UTC
- overlaygraphicsubs (VS -> V)
  Overlay graphic subtitles onto a video stream

- graphicsub2video {S -> V)
  Converts graphic subtitles to video frames (with alpha)
  Gets auto-inserted for retaining compatibility with
  sub2video command lines

Signed-off-by: softworkz <softworkz@hotmail.com>
---
 doc/filters.texi                    | 118 +++++
 libavfilter/Makefile                |   2 +
 libavfilter/allfilters.c            |   2 +
 libavfilter/vf_overlaygraphicsubs.c | 737 ++++++++++++++++++++++++++++
 4 files changed, 859 insertions(+)
 create mode 100644 libavfilter/vf_overlaygraphicsubs.c
diff mbox series

Patch

diff --git a/doc/filters.texi b/doc/filters.texi
index c3ccaf97c4..dcbe718664 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -25543,6 +25543,124 @@  tools.
 
 @c man end VIDEO SINKS
 
+@chapter Subtitle Filters
+@c man begin SUBTITLE FILTERS
+
+When you configure your FFmpeg build, you can disable any of the
+existing filters using @code{--disable-filters}.
+
+Below is a description of the currently available subtitle filters.
+
+@section graphicsub2video
+
+Renders graphic subtitles as video frames.
+
+This filter replaces the previous "sub2video" hack which did the conversion implicitly and up-front as subtitle filtering wasn't possible at that time.
+To retain compatibility with earlier sub2video command lines, this filter is being auto-inserted in those cases.
+
+For overlaying graphicsal subtitles it is recommended to use the 'overlay_graphicsubs' filter which is more efficient and takes less processing resources.
+
+This filter is still useful in cases where the overlay is done with hardware acceleration (e.g. overlay_qsv, overlay_vaapi, overlay_cuda) for preparing the overlay frames.
+
+Inputs:
+@itemize
+@item 0: Subtitles [BITMAP]
+@end itemize
+
+Outputs:
+@itemize
+@item 0: Video [RGB32]
+@end itemize
+
+
+It accepts the following parameters:
+
+@table @option
+@item size, s
+Set the size of the output video frame.
+
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Overlay PGS subtitles
+(not recommended - better use overlay_graphicsubs)
+@example
+ffmpeg -i "https://streams.videolan.org/samples/sub/PGS/Girl_With_The_Dragon_Tattoo_2%3A23%3A56.mkv" -filter_complex "[0:1]graphicsub2video[subs];[0:0][subs]overlay" output.mp4
+@end example
+
+@item
+Overlay PGS subtitles implicitly
+The graphicsub2video is inserted automatically for compatibility with legacy command lines.
+@example
+ffmpeg -i "https://streams.videolan.org/samples/sub/PGS/Girl_With_The_Dragon_Tattoo_2%3A23%3A56.mkv" -filter_complex "[0:0][0:1]overlay" output.mp4
+@end example
+@end itemize
+
+@section overlaygraphicsubs
+
+Overlay graphic subtitles onto a video stream.
+
+This filter can blend graphical subtitles on a video stream directly, i.e. without creating full-size alpha images first.
+The blending operation is limited to the area of the subtitle rectangles, which also means that no processing is done at times where no subtitles are to be displayed.
+
+Inputs:
+@itemize
+@item 0: Video [YUV420P, YUV422P, YUV444P, ARGB, RGBA, ABGR, BGRA, RGB24, BGR24]
+@item 1: Subtitles [BITMAP]
+@end itemize
+
+Outputs:
+@itemize
+@item 0: Video (same as input)
+@end itemize
+
+It accepts the following parameters:
+
+@table @option
+@item x
+@item y
+Set the expression for the x and y coordinates of the overlaid video
+on the main video. Default value is "0" for both expressions. In case
+the expression is invalid, it is set to a huge value (meaning that the
+overlay will not be displayed within the output visible area).
+
+@item eof_action
+See @ref{framesync}.
+
+@item eval
+Set when the expressions for @option{x}, and @option{y} are evaluated.
+
+It accepts the following values:
+@table @samp
+@item init
+only evaluate expressions once during the filter initialization or
+when a command is processed
+
+@item frame
+evaluate expressions for each incoming frame
+@end table
+
+Default value is @samp{frame}.
+
+@item shortest
+See @ref{framesync}.
+
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Overlay PGS subtitles
+@example
+ffmpeg -i "https://streams.videolan.org/samples/sub/PGS/Girl_With_The_Dragon_Tattoo_2%3A23%3A56.mkv" -filter_complex "[0:0][0:1]overlaygraphicsubs" output.mp4
+@end example
+@end itemize
+@c man end SUBTITLE FILTERS
+
 @chapter Multimedia Filters
 @c man begin MULTIMEDIA FILTERS
 
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 99f3047965..6c790391b8 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -293,6 +293,7 @@  OBJS-$(CONFIG_GBLUR_FILTER)                  += vf_gblur.o
 OBJS-$(CONFIG_GBLUR_VULKAN_FILTER)           += vf_gblur_vulkan.o vulkan.o vulkan_filter.o
 OBJS-$(CONFIG_GEQ_FILTER)                    += vf_geq.o
 OBJS-$(CONFIG_GRADFUN_FILTER)                += vf_gradfun.o
+OBJS-$(CONFIG_GRAPHICSUB2VIDEO_FILTER)       += vf_overlaygraphicsubs.o framesync.o
 OBJS-$(CONFIG_GRAPHMONITOR_FILTER)           += f_graphmonitor.o
 OBJS-$(CONFIG_GRAYWORLD_FILTER)              += vf_grayworld.o
 OBJS-$(CONFIG_GREYEDGE_FILTER)               += vf_colorconstancy.o
@@ -373,6 +374,7 @@  OBJS-$(CONFIG_OVERLAY_OPENCL_FILTER)         += vf_overlay_opencl.o opencl.o \
                                                 opencl/overlay.o framesync.o
 OBJS-$(CONFIG_OVERLAY_QSV_FILTER)            += vf_overlay_qsv.o framesync.o
 OBJS-$(CONFIG_OVERLAY_VULKAN_FILTER)         += vf_overlay_vulkan.o vulkan.o vulkan_filter.o
+OBJS-$(CONFIG_OVERLAYGRAPHICSUBS_FILTER)     += vf_overlaygraphicsubs.o framesync.o
 OBJS-$(CONFIG_OWDENOISE_FILTER)              += vf_owdenoise.o
 OBJS-$(CONFIG_PAD_FILTER)                    += vf_pad.o
 OBJS-$(CONFIG_PAD_OPENCL_FILTER)             += vf_pad_opencl.o opencl.o opencl/pad.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 4072f08385..825b636e60 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -354,6 +354,7 @@  extern const AVFilter ff_vf_oscilloscope;
 extern const AVFilter ff_vf_overlay;
 extern const AVFilter ff_vf_overlay_opencl;
 extern const AVFilter ff_vf_overlay_qsv;
+extern const AVFilter ff_vf_overlaygraphicsubs;
 extern const AVFilter ff_vf_overlay_vulkan;
 extern const AVFilter ff_vf_overlay_cuda;
 extern const AVFilter ff_vf_owdenoise;
@@ -539,6 +540,7 @@  extern const AVFilter ff_avf_showvolume;
 extern const AVFilter ff_avf_showwaves;
 extern const AVFilter ff_avf_showwavespic;
 extern const AVFilter ff_vaf_spectrumsynth;
+extern const AVFilter ff_svf_graphicsub2video;
 
 /* multimedia sources */
 extern const AVFilter ff_avsrc_amovie;
diff --git a/libavfilter/vf_overlaygraphicsubs.c b/libavfilter/vf_overlaygraphicsubs.c
new file mode 100644
index 0000000000..fa0b7107c8
--- /dev/null
+++ b/libavfilter/vf_overlaygraphicsubs.c
@@ -0,0 +1,737 @@ 
+/*
+ * Copyright (c) 2021 softworkz (derived from vf_overlay)
+ * 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 graphical subtitles on top of a video frame
+ */
+
+#include "libavutil/eval.h"
+#include "libavutil/imgutils.h"
+#include "libavutil/opt.h"
+#include "internal.h"
+#include "drawutils.h"
+#include "framesync.h"
+
+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
+};
+
+typedef struct OverlaySubsContext {
+    const AVClass *class;
+    int x, y;                   ///< position of overlaid picture
+    int w, h;
+    AVFrame *outpicref;
+
+    int main_is_packed_rgb;
+    uint8_t main_rgba_map[4];
+    int main_has_alpha;
+    uint8_t overlay_rgba_map[4];
+    int eval_mode;              ///< EvalMode
+
+    FFFrameSync fs;
+
+    int main_pix_step[4];       ///< steps per pixel for each plane of the main output
+    int hsub, vsub;             ///< chroma subsampling values
+    const AVPixFmtDescriptor *main_desc; ///< format descriptor for main input
+
+    double var_values[VAR_VARS_NB];
+    char *x_expr, *y_expr;
+
+    AVExpr *x_pexpr, *y_pexpr;
+
+    int pic_counter;
+} OverlaySubsContext;
+
+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
+};
+
+#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
+
+enum EvalMode {
+    EVAL_MODE_INIT,
+    EVAL_MODE_FRAME,
+    EVAL_MODE_NB
+};
+
+static av_cold void overlay_graphicsubs_uninit(AVFilterContext *ctx)
+{
+    OverlaySubsContext *s = ctx->priv;
+
+    ff_framesync_uninit(&s->fs);
+    av_expr_free(s->x_pexpr); s->x_pexpr = NULL;
+    av_expr_free(s->y_pexpr); s->y_pexpr = NULL;
+}
+
+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)
+{
+    OverlaySubsContext *s = ctx->priv;
+
+    s->var_values[VAR_X] = av_expr_eval(s->x_pexpr, s->var_values, NULL);
+    s->var_values[VAR_Y] = av_expr_eval(s->y_pexpr, s->var_values, NULL);
+    /* It is necessary if x is expressed from y  */
+    s->var_values[VAR_X] = av_expr_eval(s->x_pexpr, s->var_values, NULL);
+    s->x = normalize_xy(s->var_values[VAR_X], s->hsub);
+    s->y = normalize_xy(s->var_values[VAR_Y], s->vsub);
+}
+
+static int set_expr(AVExpr **pexpr, const char *expr, const char *option, void *log_ctx)
+{
+    int ret;
+    AVExpr *old = NULL;
+
+    if (*pexpr)
+        old = *pexpr;
+    ret = av_expr_parse(pexpr, expr, var_names,
+                        NULL, NULL, NULL, NULL, 0, log_ctx);
+    if (ret < 0) {
+        av_log(log_ctx, AV_LOG_ERROR,
+               "Error when evaluating the expression '%s' for %s\n",
+               expr, option);
+        *pexpr = old;
+        return ret;
+    }
+
+    av_expr_free(old);
+    return 0;
+}
+
+static int overlay_graphicsubs_query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats;
+    AVFilterLink *inlink0 = ctx->inputs[0];
+    AVFilterLink *inlink1 = ctx->inputs[1];
+    AVFilterLink *outlink = ctx->outputs[0];
+    int ret;
+    static const enum AVSubtitleType subtitle_fmts[] = { AV_SUBTITLE_FMT_BITMAP, AV_SUBTITLE_FMT_NONE };
+    static const enum AVPixelFormat supported_pix_fmts[] = {
+        AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV444P,
+        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
+    };
+
+    /* set input0 video formats */
+    formats = ff_make_format_list(supported_pix_fmts);
+    if ((ret = ff_formats_ref(formats, &inlink0->outcfg.formats)) < 0)
+        return ret;
+
+    /* set output0 video formats */
+    if ((ret = ff_formats_ref(formats, &outlink->incfg.formats)) < 0)
+        return ret;
+
+    /* set input1 subtitle formats */
+    formats = ff_make_format_list(subtitle_fmts);
+    if ((ret = ff_formats_ref(formats, &inlink1->outcfg.formats)) < 0)
+        return ret;
+
+    return 0;
+}
+
+static int config_output(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    OverlaySubsContext *s = ctx->priv;
+    int ret;
+
+    if ((ret = ff_framesync_init_dualinput(&s->fs, ctx)) < 0)
+        return ret;
+
+    outlink->w = ctx->inputs[MAIN]->w;
+    outlink->h = ctx->inputs[MAIN]->h;
+    outlink->time_base = ctx->inputs[MAIN]->time_base;
+
+    return ff_framesync_configure(&s->fs);
+}
+
+// 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 non-pre-multiplied 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 av_always_inline void blend_packed_rgb(const AVFilterContext *ctx,
+    const AVFrame *dst, const AVSubtitleArea *src,
+    int x, int y,
+    int is_straight)
+{
+    OverlaySubsContext *s = ctx->priv;
+    int i, imax, j, jmax;
+    const int src_w = src->w;
+    const int src_h = src->h;
+    const int dst_w = dst->width;
+    const int dst_h = dst->height;
+    uint8_t alpha;          ///< the amount of overlay to blend on to main
+    const int dr = s->main_rgba_map[R];
+    const int dg = s->main_rgba_map[G];
+    const int db = s->main_rgba_map[B];
+    const int da = s->main_rgba_map[A];
+    const int dstep = s->main_pix_step[0];
+    const int sr = s->overlay_rgba_map[R];
+    const int sg = s->overlay_rgba_map[G];
+    const int sb = s->overlay_rgba_map[B];
+    const int sa = s->overlay_rgba_map[A];
+    int slice_start, slice_end;
+    uint8_t *S, *sp, *d, *dp;
+
+    i = FFMAX(-y, 0);
+    imax = FFMIN3(-y + dst_h, FFMIN(src_h, dst_h), y + src_h);
+
+    slice_start = i;
+    slice_end = i + imax;
+
+    sp = src->buf[0]->data + slice_start       * src->linesize[0];
+    dp = dst->data[0] + (slice_start + y) * dst->linesize[0];
+
+    for (i = slice_start; i < slice_end; i++) {
+        j = FFMAX(-x, 0);
+        S = sp + j;
+        d = dp + ((x + j) * dstep);
+
+        for (jmax = FFMIN(-x + dst_w, src_w); j < jmax; j++) {
+            uint32_t val = src->pal[*S];
+            const uint8_t *sval = (uint8_t *)&val;
+            alpha = sval[sa];
+
+            // if the main channel has an alpha channel, alpha has to be calculated
+            // to create an un-premultiplied (straight) alpha value
+            if (s->main_has_alpha && alpha != 0 && alpha != 255) {
+                const uint8_t alpha_d = d[da];
+                alpha = UNPREMULTIPLY_ALPHA(alpha, alpha_d);
+            }
+
+            switch (alpha) {
+            case 0:
+                break;
+            case 255:
+                d[dr] = sval[sr];
+                d[dg] = sval[sg];
+                d[db] = sval[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] = is_straight ? FAST_DIV255(d[dr] * (255 - alpha) + sval[sr] * alpha) :
+                        FFMIN(FAST_DIV255(d[dr] * (255 - alpha)) + sval[sr], 255);
+                d[dg] = is_straight ? FAST_DIV255(d[dg] * (255 - alpha) + sval[sg] * alpha) :
+                        FFMIN(FAST_DIV255(d[dg] * (255 - alpha)) + sval[sg], 255);
+                d[db] = is_straight ? FAST_DIV255(d[db] * (255 - alpha) + sval[sb] * alpha) :
+                        FFMIN(FAST_DIV255(d[db] * (255 - alpha)) + sval[sb], 255);
+            }
+
+            if (s->main_has_alpha) {
+                switch (alpha) {
+                case 0:
+                    break;
+                case 255:
+                    d[da] = sval[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 += 1;
+        }
+        dp += dst->linesize[0];
+        sp += src->linesize[0];
+    }
+}
+
+static av_always_inline void blend_plane_8_8bits(const AVFilterContext *ctx, const AVFrame *dst, const AVSubtitleArea *area,
+    const uint32_t *yuv_pal, int src_w, int src_h, int dst_w, int dst_h, int plane, int hsub, int vsub,
+    int x, int y, int dst_plane, int dst_offset, int dst_step)
+{
+    const int src_wp = AV_CEIL_RSHIFT(src_w, hsub);
+    const int src_hp = AV_CEIL_RSHIFT(src_h, vsub);
+    const int dst_wp = AV_CEIL_RSHIFT(dst_w, hsub);
+    const int dst_hp = AV_CEIL_RSHIFT(dst_h, vsub);
+    const int yp = y >> vsub;
+    const int xp = x >> hsub;
+    uint8_t *s, *sp, *d, *dp, *dap;
+    int imax, i, j, jmax;
+    int slice_start, slice_end;
+
+    i = FFMAX(-yp, 0);                                                                                     \
+    imax = FFMIN3(-yp + dst_hp, FFMIN(src_hp, dst_hp), yp + src_hp);                                       \
+
+    slice_start = i;
+    slice_end = i + imax;
+
+    sp = area->buf[0]->data + (slice_start << vsub) * area->linesize[0];
+    dp = dst->data[dst_plane] + (yp + slice_start) * dst->linesize[dst_plane] + dst_offset;
+
+    dap = dst->data[3] + ((yp + slice_start) << vsub) * dst->linesize[3];
+
+    for (i = slice_start; i < slice_end; i++) {
+        j = FFMAX(-xp, 0);
+        d = dp + (xp + j) * dst_step;
+        s = sp + (j << hsub);
+        jmax = FFMIN(-xp + dst_wp, src_wp);    
+
+        for (; j < jmax; j++) {
+            uint32_t val = yuv_pal[*s];
+            const uint8_t *sval = (uint8_t *)&val;
+            const int alpha = sval[3];
+            const int max = 255, mid = 128;
+            const int d_int = *d;
+            const int sval_int = sval[plane];
+
+            switch (alpha) {
+            case 0:
+                break;
+            case 255:
+                *d = sval[plane];
+                break;
+            default:
+                if (plane > 0)
+                    *d = av_clip(FAST_DIV255((d_int - mid) * (max - alpha) + (sval_int - mid) * alpha) , -mid, mid) + mid;
+                else
+                    *d = FAST_DIV255(d_int * (max - alpha) + sval_int * alpha);
+                break;
+            }
+
+            d += dst_step;
+            s += 1 << hsub;
+        }
+        dp += dst->linesize[dst_plane];
+        sp +=  (1 << vsub) * area->linesize[0];
+        dap += (1 << vsub) * dst->linesize[3];
+    }
+}
+
+#define RGB2Y(r, g, b) (uint8_t)(((66 * (r) + 129 * (g) +  25 * (b) + 128) >> 8) +  16)
+#define RGB2U(r, g, b) (uint8_t)(((-38 * (r) - 74 * (g) + 112 * (b) + 128) >> 8) + 128)
+#define RGB2V(r, g, b) (uint8_t)(((112 * (r) - 94 * (g) -  18 * (b) + 128) >> 8) + 128)
+/* Converts R8 G8 B8 color to YUV. */
+static av_always_inline void rgb_2_yuv(uint8_t r, uint8_t g, uint8_t b, uint8_t* y, uint8_t* u, uint8_t* v)
+{
+    *y = RGB2Y((int)r, (int)g, (int)b);
+    *u = RGB2U((int)r, (int)g, (int)b);
+    *v = RGB2V((int)r, (int)g, (int)b);
+}
+
+
+static av_always_inline void blend_yuv_8_8bits(AVFilterContext *ctx, AVFrame *dst, const AVSubtitleArea *area, int hsub, int vsub, int x, int y)
+{
+    OverlaySubsContext *s = ctx->priv;
+    const int src_w = area->w;
+    const int src_h = area->h;
+    const int dst_w = dst->width;
+    const int dst_h = dst->height;
+    const int sr = s->overlay_rgba_map[R];
+    const int sg = s->overlay_rgba_map[G];
+    const int sb = s->overlay_rgba_map[B];
+    const int sa = s->overlay_rgba_map[A];
+    uint32_t yuvpal[256];
+
+    for (int i = 0; i < 256; ++i) {
+        const uint8_t *rgba = (const uint8_t *)&area->pal[i];
+        uint8_t *yuva = (uint8_t *)&yuvpal[i];
+        rgb_2_yuv(rgba[sr], rgba[sg], rgba[sb], &yuva[Y], &yuva[U], &yuva[V]);
+        yuva[3] = rgba[sa];
+    }
+
+    blend_plane_8_8bits(ctx, dst, area, yuvpal, src_w, src_h, dst_w, dst_h, Y, 0,    0,    x, y, s->main_desc->comp[Y].plane, s->main_desc->comp[Y].offset, s->main_desc->comp[Y].step);
+    blend_plane_8_8bits(ctx, dst, area, yuvpal, src_w, src_h, dst_w, dst_h, U, hsub, vsub, x, y, s->main_desc->comp[U].plane, s->main_desc->comp[U].offset, s->main_desc->comp[U].step);
+    blend_plane_8_8bits(ctx, dst, area, yuvpal, src_w, src_h, dst_w, dst_h, V, hsub, vsub, x, y, s->main_desc->comp[V].plane, s->main_desc->comp[V].offset, s->main_desc->comp[V].step);
+}
+
+static int config_input_main(AVFilterLink *inlink)
+{
+    int ret;
+    AVFilterContext *ctx  = inlink->dst;
+    OverlaySubsContext *s = inlink->dst->priv;
+    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(inlink->format);
+
+    av_image_fill_max_pixsteps(s->main_pix_step,    NULL, pix_desc);
+    ff_fill_rgba_map(s->overlay_rgba_map, AV_PIX_FMT_RGB32); // it's actually AV_PIX_FMT_PAL8);
+
+    s->hsub = pix_desc->log2_chroma_w;
+    s->vsub = pix_desc->log2_chroma_h;
+
+    s->main_desc = pix_desc;
+
+    s->main_is_packed_rgb = ff_fill_rgba_map(s->main_rgba_map, inlink->format) >= 0;
+    s->main_has_alpha = !!(pix_desc->flags & AV_PIX_FMT_FLAG_ALPHA);
+
+    /* Finish the configuration by evaluating the expressions
+       now when both inputs are configured. */
+    s->var_values[VAR_MAIN_W   ] = s->var_values[VAR_MW] = ctx->inputs[MAIN   ]->w;
+    s->var_values[VAR_MAIN_H   ] = s->var_values[VAR_MH] = ctx->inputs[MAIN   ]->h;
+    s->var_values[VAR_OVERLAY_W] = s->var_values[VAR_OW] = ctx->inputs[OVERLAY]->w;
+    s->var_values[VAR_OVERLAY_H] = s->var_values[VAR_OH] = ctx->inputs[OVERLAY]->h;
+    s->var_values[VAR_HSUB]  = 1<<pix_desc->log2_chroma_w;
+    s->var_values[VAR_VSUB]  = 1<<pix_desc->log2_chroma_h;
+    s->var_values[VAR_X]     = NAN;
+    s->var_values[VAR_Y]     = NAN;
+    s->var_values[VAR_N]     = 0;
+    s->var_values[VAR_T]     = NAN;
+    s->var_values[VAR_POS]   = NAN;
+
+    if ((ret = set_expr(&s->x_pexpr,      s->x_expr,      "x",      ctx)) < 0 ||
+        (ret = set_expr(&s->y_pexpr,      s->y_expr,      "y",      ctx)) < 0)
+        return ret;
+
+    if (s->eval_mode == EVAL_MODE_INIT) {
+        eval_expr(ctx);
+        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d\n",
+               s->var_values[VAR_X], s->x,
+               s->var_values[VAR_Y], s->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;
+}
+
+static int do_blend(FFFrameSync *fs)
+{
+    AVFilterContext *ctx = fs->parent;
+    AVFrame *mainpic, *second;
+    OverlaySubsContext *s = ctx->priv;
+    AVFilterLink *inlink = ctx->inputs[0];
+    unsigned i;
+    int ret;
+
+    ret = ff_framesync_dualinput_get_writable(fs, &mainpic, &second);
+    if (ret < 0)
+        return ret;
+    if (!second)
+        return ff_filter_frame(ctx->outputs[0], mainpic);
+
+    if (s->eval_mode == EVAL_MODE_FRAME) {
+        int64_t pos = mainpic->pkt_pos;
+
+        s->var_values[VAR_N] = (double)inlink->frame_count_out;
+        s->var_values[VAR_T] = mainpic->pts == AV_NOPTS_VALUE ?
+            NAN :(double)mainpic->pts * av_q2d(inlink->time_base);
+        s->var_values[VAR_POS] = pos == -1 ? NAN : (double)pos;
+
+        s->var_values[VAR_OVERLAY_W] = s->var_values[VAR_OW] = second->width;
+        s->var_values[VAR_OVERLAY_H] = s->var_values[VAR_OH] = second->height;
+        s->var_values[VAR_MAIN_W   ] = s->var_values[VAR_MW] = mainpic->width;
+        s->var_values[VAR_MAIN_H   ] = s->var_values[VAR_MH] = mainpic->height;
+
+        eval_expr(ctx);
+        av_log(ctx, AV_LOG_DEBUG, "n:%f t:%f pos:%f x:%f xi:%d y:%f yi:%d\n",
+               s->var_values[VAR_N], s->var_values[VAR_T], s->var_values[VAR_POS],
+               s->var_values[VAR_X], s->x,
+               s->var_values[VAR_Y], s->y);
+    }
+
+    for (i = 0; i < second->num_subtitle_areas; i++) {
+        const AVSubtitleArea *sub_area = second->subtitle_areas[i];
+
+        if (sub_area->type != AV_SUBTITLE_FMT_BITMAP) {
+            av_log(NULL, AV_LOG_WARNING, "overlay_graphicsub: non-bitmap subtitle\n");
+            return AVERROR_INVALIDDATA;
+        }
+
+        switch (inlink->format) {
+        case AV_PIX_FMT_YUV420P:
+            blend_yuv_8_8bits(ctx, mainpic, sub_area, 1, 1, sub_area->x + s->x, sub_area->y + s->y);
+            break;
+        case AV_PIX_FMT_YUV422P:
+            blend_yuv_8_8bits(ctx, mainpic, sub_area, 1, 0, sub_area->x + s->x, sub_area->y + s->y);
+            break;
+        case AV_PIX_FMT_YUV444P:
+            blend_yuv_8_8bits(ctx, mainpic, sub_area, 0, 0, sub_area->x + s->x, sub_area->y + s->y);
+            break;
+        case AV_PIX_FMT_RGB24:
+        case AV_PIX_FMT_BGR24:
+        case AV_PIX_FMT_ARGB:
+        case AV_PIX_FMT_RGBA:
+        case AV_PIX_FMT_BGRA:
+        case AV_PIX_FMT_ABGR:
+            blend_packed_rgb(ctx, mainpic, sub_area, sub_area->x + s->x, sub_area->y + s->y, 1);
+            break;
+        default:
+            av_log(NULL, AV_LOG_ERROR, "Unsupported input pix fmt: %d\n", inlink->format);
+            return AVERROR(EINVAL);
+        }
+    }
+
+    return ff_filter_frame(ctx->outputs[0], mainpic);
+}
+
+static av_cold int overlay_graphicsubs_init(AVFilterContext *ctx)
+{
+    OverlaySubsContext *s = ctx->priv;
+
+    s->fs.on_event = do_blend;
+    return 0;
+}
+
+static int overlay_graphicsubs_activate(AVFilterContext *ctx)
+{
+    OverlaySubsContext *s = ctx->priv;
+    return ff_framesync_activate(&s->fs);
+}
+
+static int graphicsub2video_query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats;
+    AVFilterLink *inlink = ctx->inputs[0];
+    AVFilterLink *outlink = ctx->outputs[0];
+    static const enum AVSubtitleType subtitle_fmts[] = { AV_SUBTITLE_FMT_BITMAP, AV_SUBTITLE_FMT_NONE };
+    static const enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_RGB32, AV_PIX_FMT_NONE };
+    int ret;
+
+    /* set input subtitle formats */
+    formats = ff_make_format_list(subtitle_fmts);
+    if ((ret = ff_formats_ref(formats, &inlink->outcfg.formats)) < 0)
+        return ret;
+
+    /* set output video formats */
+    formats = ff_make_format_list(pix_fmts);
+    if ((ret = ff_formats_ref(formats, &outlink->incfg.formats)) < 0)
+        return ret;
+
+    return 0;
+}
+
+static int graphicsub2video_config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    OverlaySubsContext *s = ctx->priv;
+
+    if (s->w <= 0 || s->h <= 0) {
+        s->w = inlink->w;
+        s->h = inlink->h;
+    }
+    return 0;
+}
+
+static int graphicsub2video_config_output(AVFilterLink *outlink)
+{
+    const AVFilterContext *ctx  = outlink->src;
+    OverlaySubsContext *s = ctx->priv;
+    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(outlink->format);
+
+    outlink->w = s->w;
+    outlink->h = s->h;
+    outlink->sample_aspect_ratio = (AVRational){1,1};
+    outlink->time_base = ctx->inputs[0]->time_base;
+
+    av_image_fill_max_pixsteps(s->main_pix_step, NULL, pix_desc);
+    ff_fill_rgba_map(s->overlay_rgba_map, AV_PIX_FMT_RGB32);
+
+    s->hsub = pix_desc->log2_chroma_w;
+    s->vsub = pix_desc->log2_chroma_h;
+
+    s->main_desc = pix_desc;
+
+    s->main_is_packed_rgb = ff_fill_rgba_map(s->main_rgba_map, outlink->format) >= 0;
+    s->main_has_alpha = !!(pix_desc->flags & AV_PIX_FMT_FLAG_ALPHA);
+
+    return 0;
+}
+
+static int graphicsub2video_filter_frame(AVFilterLink *inlink, AVFrame *src_frame)
+{
+    AVFilterLink *outlink = inlink->dst->outputs[0];
+    const AVFilterContext *ctx  = outlink->src;
+    OverlaySubsContext *s = ctx->priv;
+    AVFrame *out;
+    const unsigned num_rects = src_frame->num_subtitle_areas;
+    unsigned int i;
+
+    out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
+    if (!out) {
+        av_frame_free(&src_frame);
+        return AVERROR(ENOMEM);
+    }
+
+    // Maybe we should set these..
+    ////out->color_primaries = AVCOL_PRI_BT709;
+    ////out->color_range = AVCOL_RANGE_MPEG;
+    ////out->color_trc = AVCOL_TRC_BT709;
+
+    memset(out->data[0], 0, (size_t)out->linesize[0] * out->height);
+
+    out->pts = out->pkt_dts = out->best_effort_timestamp = src_frame->pts;
+    out->coded_picture_number = out->display_picture_number = s->pic_counter++;
+
+    for (i = 0; i < num_rects; i++) {
+        const AVSubtitleArea  *sub_rect = src_frame->subtitle_areas[i];
+
+        if (sub_rect->type != AV_SUBTITLE_FMT_BITMAP) {
+            av_log(NULL, AV_LOG_WARNING, "sub2video: non-bitmap subtitle\n");
+            av_frame_free(&src_frame);
+            return AVERROR_INVALIDDATA;
+        }
+
+        blend_packed_rgb(inlink->dst, out, sub_rect, sub_rect->x, sub_rect->y, 1);
+    }
+
+    av_log(inlink->dst, AV_LOG_DEBUG, "graphicsub2video output - size %dx%d  pts: %"PRId64"  areas: %d\n", out->width, out->height, out->pts, src_frame->num_subtitle_areas);
+
+    av_frame_free(&src_frame);
+    return ff_filter_frame(outlink, out);
+}
+
+#define OFFSET(x) offsetof(OverlaySubsContext, x)
+#define FLAGS (AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM)
+
+static const AVOption overlaygraphicsubs_options[] = {
+    { "x", "set the x expression", OFFSET(x_expr), AV_OPT_TYPE_STRING, {.str = "0"}, 0, 0, .flags = FLAGS },
+    { "y", "set the y expression", OFFSET(y_expr), AV_OPT_TYPE_STRING, {.str = "0"}, 0, 0, .flags = FLAGS },
+    { "eof_action", "Action to take when encountering EOF from secondary input ",
+        OFFSET(fs.opt_eof_action), AV_OPT_TYPE_INT, { .i64 = EOF_ACTION_REPEAT },
+        EOF_ACTION_REPEAT, EOF_ACTION_PASS, .flags = FLAGS, "eof_action" },
+        { "repeat", "Repeat the previous frame.",   0, AV_OPT_TYPE_CONST, { .i64 = EOF_ACTION_REPEAT }, .flags = FLAGS, "eof_action" },
+        { "endall", "End both streams.",            0, AV_OPT_TYPE_CONST, { .i64 = EOF_ACTION_ENDALL }, .flags = FLAGS, "eof_action" },
+        { "pass",   "Pass through the main input.", 0, AV_OPT_TYPE_CONST, { .i64 = EOF_ACTION_PASS },   .flags = FLAGS, "eof_action" },
+    { "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" },
+    { "shortest", "force termination when the shortest input terminates", OFFSET(fs.opt_shortest), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, .flags = FLAGS },
+    { "repeatlast", "repeat overlay of the last overlay frame", OFFSET(fs.opt_repeatlast), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, .flags = FLAGS },
+    { NULL }
+};
+
+static const AVOption graphicsub2video_options[] = {
+    { "size", "set video size", OFFSET(w), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL}, 0, 0, .flags = FLAGS },
+    { "s",    "set video size", OFFSET(w), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL}, 0, 0, .flags = FLAGS },
+    { NULL }
+};
+
+FRAMESYNC_DEFINE_CLASS(overlaygraphicsubs, OverlaySubsContext, fs);
+
+static const AVFilterPad overlaygraphicsubs_inputs[] = {
+    {
+        .name         = "main",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .config_props = config_input_main,
+        .flags        = AVFILTERPAD_FLAG_NEEDS_WRITABLE,
+    },
+    {
+        .name         = "overlay",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+    },
+};
+
+static const AVFilterPad overlaygraphicsubs_outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_VIDEO,
+        .config_props  = config_output,
+    },
+};
+
+const AVFilter ff_vf_overlaygraphicsubs = {
+    .name          = "overlaygraphicsubs",
+    .description   = NULL_IF_CONFIG_SMALL("Overlay graphical subtitles on top of the input."),
+    .preinit       = overlaygraphicsubs_framesync_preinit,
+    .init          = overlay_graphicsubs_init,
+    .uninit        = overlay_graphicsubs_uninit,
+    .priv_size     = sizeof(OverlaySubsContext),
+    .priv_class    = &overlaygraphicsubs_class,
+    .activate      = overlay_graphicsubs_activate,
+    FILTER_INPUTS(overlaygraphicsubs_inputs),
+    FILTER_OUTPUTS(overlaygraphicsubs_outputs),
+    FILTER_QUERY_FUNC(overlay_graphicsubs_query_formats),
+};
+
+AVFILTER_DEFINE_CLASS(graphicsub2video);
+
+static const AVFilterPad graphicsub2video_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+        .filter_frame = graphicsub2video_filter_frame,
+        .config_props = graphicsub2video_config_input,
+    },
+};
+
+static const AVFilterPad graphicsub2video_outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_VIDEO,
+        .config_props  = graphicsub2video_config_output,
+    },
+};
+
+const AVFilter ff_svf_graphicsub2video = {
+    .name          = "graphicsub2video",
+    .description   = NULL_IF_CONFIG_SMALL("Convert graphical subtitles to video"),
+    .priv_size     = sizeof(OverlaySubsContext),
+    .priv_class    = &graphicsub2video_class,
+    FILTER_INPUTS(graphicsub2video_inputs),
+    FILTER_OUTPUTS(graphicsub2video_outputs),
+    FILTER_QUERY_FUNC(graphicsub2video_query_formats),
+};