[FFmpeg-devel] [PATCH v5 21/25] avfilter/text2graphicsub: Added text2graphicsub subtitle filter

[tcoza <ffmpegagent@gmail.com>]

From: tcoza <traian.coza@gmail.com>

Added a text2graphicsub subtitle filter which converts text-based
subtitle tracks to bitmap-based subtitle tracks. The filter uses libass
to render the subtitles.
It takes as parameters an output height and width, as well as a number
of colors in the output palette as well as sources of fonts. All its
arguments are optional.

Reviewed-by: softworkz <softworkz@hotmail.com>
Signed-off-by: softworkz <softworkz@hotmail.com>
Signed-off-by: tcoza <traian.coza@gmail.com>
---
 configure                        |   1 +
 doc/filters.texi                 |  51 +++
 libavfilter/Makefile             |   1 +
 libavfilter/allfilters.c         |   1 +
 libavfilter/sf_text2graphicsub.c | 630 +++++++++++++++++++++++++++++++
 5 files changed, 684 insertions(+)
 create mode 100644 libavfilter/sf_text2graphicsub.c

diff --git a/configure b/configure
index 89db322fb8..f74077b439 100755
--- a/configure
+++ b/configure
@@ -3734,6 +3734,7 @@ subscale_filter_deps="swscale avcodec"
 subtitles_filter_deps="avformat avcodec libass"
 super2xsai_filter_deps="gpl"
 pixfmts_super2xsai_test_deps="super2xsai_filter"
+text2graphicsub_filter_deps="avformat avcodec libass"
 textsub2video_filter_deps="avcodec libass"
 tinterlace_filter_deps="gpl"
 tinterlace_merge_test_deps="tinterlace_filter"
diff --git a/doc/filters.texi b/doc/filters.texi
index 00fa9bbac5..56da160634 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -27744,6 +27744,57 @@ ffmpeg -y -y -loglevel verbose -i "https://streams.videolan.org/samples/sub/larg
 @end example
 @end itemize
 
+@section text2graphicsub
+
+Converts a text-based subtitle track to a bitmap-based subtitle track.
+
+The text2graphicsub filter uses libass to render all the subtitle
+frames in a text-based subtitle track (such as srt or ass) to allow
+its encoding with a bitmap-based subtitle encoder (such as dvd_subtitle).
+
+Inputs:
+- 0: Subtitles [text]
+
+Outputs:
+- 0: Subtitles [bitmap]
+
+It accepts the following parameters:
+
+@table @option
+
+@item s, size
+Set the size of the output. Default from input track.
+
+@item n, num_colors
+Set the number of palette colors for output images,
+Range [2,256]. Default 16.
+
+@item f, filename
+Set the media container from which to extract fonts required
+for rendering the subtitles, usually the same as the input
+track's media container. Can be omitted.
+
+@item fd, fontsdir
+Set the directory from which to load fonts required for
+rendering the subtitles. Can be used with 'fonts'. Can be omitted.
+
+@item ss, stripstyles
+Remove certain styles from an ass track which do not render well.
+Stripped styles include blurs, fades, and other animations.
+Default yes.
+
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Convert a video's text-based subtitle track to a dvd_subtitle subtitle track.
+@example
+ffmpeg -i video.mkv -map 0:v -map 0:a -filter_complex [0:s]text2graphicsub=f=video.mkv[dvd_sub] -map [dvd_sub] -c copy -c:s dvd_subtitle output.mkv
+@end example
+@end itemize
+
 @c man end SUBTITLE FILTERS
 
 @chapter Multimedia Filters
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 780e5333a0..adbc16a5a9 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -585,6 +585,7 @@ OBJS-$(CONFIG_SPLITCC_FILTER)                += sf_splitcc.o
 OBJS-$(CONFIG_STRIPSTYLES_FILTER)            += sf_stripstyles.o
 OBJS-$(CONFIG_SUBFEED_FILTER)                += sf_subfeed.o
 OBJS-$(CONFIG_SUBSCALE_FILTER)               += sf_subscale.o
+OBJS-$(CONFIG_TEXT2GRAPHICSUB_FILTER)        += sf_text2graphicsub.o
 OBJS-$(CONFIG_TEXTMOD_FILTER)                += sf_textmod.o
 
 # multimedia filters
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index ff56661b67..82297e9657 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -577,6 +577,7 @@ extern const AVFilter ff_sf_splitcc;
 extern const AVFilter ff_sf_stripstyles;
 extern const AVFilter ff_sf_subfeed;
 extern const AVFilter ff_sf_subscale;
+extern const AVFilter ff_sf_text2graphicsub;
 extern const AVFilter ff_sf_textmod;
 
 /* those filters are part of public or internal API,
diff --git a/libavfilter/sf_text2graphicsub.c b/libavfilter/sf_text2graphicsub.c
new file mode 100644
index 0000000000..072d70d51a
--- /dev/null
+++ b/libavfilter/sf_text2graphicsub.c
@@ -0,0 +1,630 @@
+/*
+ * Copyright (c) 2021 tcoza
+ *
+ * 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
+ * convert text subtitles to bitmap subtitles filter
+ */
+
+#include <ass/ass.h>
+#include "libavutil/avstring.h"
+
+#include "internal.h"
+#include "avfilter.h"
+#include "drawutils.h"
+#include "libavutil/opt.h"
+#include "libavutil/buffer.h"
+#include "libavutil/internal.h"
+#include "libavformat/avformat.h"
+#include "libavcodec/elbg.h"
+#include "libavutil/ass_split_internal.h"
+#include "libavutil/ass_internal.h"
+#include "libavutil/lfg.h"
+
+typedef struct PalettizeContext {
+    int *codeword, *codebook;
+    int *codeword_closest_codebook_idxs;
+    int r_idx, g_idx, b_idx, a_idx;
+    struct ELBGContext *elbg;
+    AVLFG lfg;
+} PalettizeContext;
+
+typedef struct Text2GraphicSubContext {
+    const AVClass *class;
+    ASS_Library *library;
+    ASS_Renderer *renderer;
+    ASS_Track *track;
+    PalettizeContext *palettize_context;
+    FFDrawContext draw_context;
+    struct { int width; int height; } size;
+    int num_colors, stripstyles;
+    char *filename, *fontsdir, *force_style;
+    int got_header;
+} Text2GraphicSubContext;
+
+typedef struct DialogContext {
+    int is_animated;
+    int has_text;
+} DialogContext;
+
+static void dialog_text_cb(void *priv, const char *text, int len)
+{
+    DialogContext *s = priv;
+    if (!s->is_animated )
+        s->has_text = 1;
+}
+
+static void dialog_drawing_mode_cb(void *priv, int scale)
+{
+    DialogContext *s = priv;
+    s->is_animated = 1;
+}
+
+static void dialog_animate_cb(void *priv, int t1, int t2, int accel, char *style)
+{
+    DialogContext *s = priv;
+    s->is_animated = 1;
+}
+
+static void dialog_move_cb(void *priv, int x1, int y1, int x2, int y2, int t1, int t2)
+{
+    DialogContext *s = priv;
+    if (t1 >= 0 || t2 >= 0)
+        s->is_animated = 1;
+}
+
+static const ASSCodesCallbacks dialog_callbacks = {
+    .text             = dialog_text_cb,
+    .drawing_mode     = dialog_drawing_mode_cb,
+    .animate          = dialog_animate_cb,
+    .move             = dialog_move_cb,
+};
+
+static char *process_dialog(const char *ass_line)
+{
+    DialogContext dlg_ctx = { 0 };
+    ASSDialog *dialog = avpriv_ass_split_dialog(NULL, ass_line);
+    AVBPrint buffer;
+    char *result = NULL;
+
+    if (!dialog)
+        return NULL;
+
+    av_bprint_init(&buffer, 512, AV_BPRINT_SIZE_UNLIMITED);
+
+    avpriv_ass_filter_override_codes(&dialog_callbacks, &dlg_ctx, dialog->text, &buffer, ASS_SPLIT_BASIC);
+
+    if (av_bprint_is_complete(&buffer) && buffer.len > 0 && dlg_ctx.has_text > 0)
+        result = avpriv_ass_get_dialog_ex(dialog->readorder, dialog->layer, dialog->style, dialog->name, dialog->margin_l, dialog->margin_r, dialog->margin_v, dialog->effect, buffer.str);
+
+    av_bprint_finalize(&buffer, NULL);
+    avpriv_ass_free_dialog(&dialog);
+
+    return result;
+}
+
+static void palettize_image(PalettizeContext *const s,
+                           const int w, const int h,
+                           uint8_t *src_data, const int src_linesize,
+                           uint8_t *dst_data, const int dst_linesize,
+                           uint32_t *dst_pal, const int num_colors)
+{
+    const int codeword_length = w * h;
+
+    /* Re-Initialize */
+    s->codeword = av_realloc_f(s->codeword, codeword_length, 4 * sizeof(*s->codeword));
+    s->codeword_closest_codebook_idxs = av_realloc_f(
+        s->codeword_closest_codebook_idxs, codeword_length,
+        sizeof(*s->codeword_closest_codebook_idxs));
+    s->codebook = av_realloc_f(s->codebook, num_colors, 4 * sizeof(*s->codebook));
+
+    /* build the codeword */
+    for (int k = 0, i = 0; i < h; i++)
+        for (int j = 0; j < w; j++) {
+            s->codeword[k++] = src_data[i * src_linesize + j * 4 + s->b_idx];
+            s->codeword[k++] = src_data[i * src_linesize + j * 4 + s->g_idx];
+            s->codeword[k++] = src_data[i * src_linesize + j * 4 + s->r_idx];
+            s->codeword[k++] = src_data[i * src_linesize + j * 4 + s->a_idx];
+        }
+
+    /* compute the codebook */
+    avpriv_elbg_do(&s->elbg, s->codeword, 4,
+        codeword_length, s->codebook, num_colors, 1,
+        s->codeword_closest_codebook_idxs, &s->lfg, 0);
+
+    /* Write Palette */
+    for (int i = 0; i < num_colors; i++)
+        dst_pal[i] = (s->codebook[i*4+3] << 24) |
+                     (s->codebook[i*4+2] << 16) |
+                     (s->codebook[i*4+1] <<  8) |
+                     (s->codebook[i*4+0] <<  0);
+
+    /* Write Image */
+    for (int k = 0, i = 0; i < h; i++)
+        for (int j = 0; j < w; j++)
+            dst_data[i * dst_linesize + j] =
+                s->codeword_closest_codebook_idxs[k++];
+}
+
+static void init_palettizecontext(PalettizeContext **palettizecontext)
+{
+    uint8_t rgba_map[4];
+    PalettizeContext *context = (PalettizeContext *)av_malloc(sizeof(PalettizeContext));
+    context->codebook = NULL;
+    context->codeword = NULL;
+    context->codeword_closest_codebook_idxs = NULL;
+    context->elbg = NULL;
+    av_lfg_init(&context->lfg, 0xACBADF);
+    ff_fill_rgba_map(&rgba_map[0], AV_PIX_FMT_RGB32);
+    context->r_idx = rgba_map[0]; // R
+    context->g_idx = rgba_map[1]; // G
+    context->b_idx = rgba_map[2]; // B
+    context->a_idx = rgba_map[3]; // A
+    *palettizecontext = context;
+}
+
+static void free_palettizecontext(PalettizeContext **palettizecontext)
+{
+    PalettizeContext *context = *palettizecontext;
+    av_freep(&context->codebook);
+    av_freep(&context->codeword);
+    av_freep(&context->codeword_closest_codebook_idxs);
+    avpriv_elbg_free(&context->elbg);
+    av_free(context);
+    *palettizecontext = NULL;
+}
+
+/* libass supports a log level ranging from 0 to 7 */
+static const int ass_libavfilter_log_level_map[] = {
+    [0] = AV_LOG_FATAL,     /* MSGL_FATAL */
+    [1] = AV_LOG_ERROR,     /* MSGL_ERR */
+    [2] = AV_LOG_WARNING,   /* MSGL_WARN */
+    [3] = AV_LOG_WARNING,   /* <undefined> */
+    [4] = AV_LOG_INFO,      /* MSGL_INFO */
+    [5] = AV_LOG_INFO,      /* <undefined> */
+    [6] = AV_LOG_VERBOSE,   /* MSGL_V */
+    [7] = AV_LOG_DEBUG,     /* MSGL_DBG2 */
+};
+
+static void ass_log(int ass_level, const char *fmt, va_list args, void *ctx)
+{
+    const int ass_level_clip = av_clip(ass_level, 0,
+        FF_ARRAY_ELEMS(ass_libavfilter_log_level_map) - 1);
+    const int level = ass_libavfilter_log_level_map[ass_level_clip];
+    av_vlog(ctx, level, fmt, args);
+    av_log(ctx, level, "\n");
+}
+
+static const char * const font_mimetypes[] = {
+    "font/ttf",
+    "font/otf",
+    "font/sfnt",
+    "font/woff",
+    "font/woff2",
+    "application/font-sfnt",
+    "application/font-woff",
+    "application/x-truetype-font",
+    "application/vnd.ms-opentype",
+    "application/x-font-ttf",
+    NULL
+};
+
+static int stream_is_font(AVStream* st)
+{
+    const AVDictionaryEntry *tag = NULL;
+
+    if (st->codecpar->codec_type != AVMEDIA_TYPE_ATTACHMENT)
+        return 0;
+
+    tag = av_dict_get(st->metadata, "mimetype", NULL, AV_DICT_MATCH_CASE);
+    if (!tag) return 0;
+    for (int i = 0; font_mimetypes[i]; i++)
+        if (av_strcasecmp(font_mimetypes[i], tag->value) == 0)
+            return 1;
+    return 0;
+}
+
+#define AR(c)  (((c)>>24)&0xFF)
+#define AG(c)  (((c)>>16)&0xFF)
+#define AB(c)  (((c)>> 8)&0xFF)
+#define AA(c)  ((0xFF-(c))&0xFF)
+
+static void set_area_bounds(ASS_Image *image, AVSubtitleArea *area)
+{
+    int x_min = INT_MAX, y_min = INT_MAX;
+    int x_max = 0, y_max = 0;
+    int stride_max = 0;
+
+    for (ASS_Image *img = image; img != NULL; img = img->next)
+    {
+        x_min = FFMIN(x_min, img->dst_x);
+        y_min = FFMIN(y_min, img->dst_y);
+        x_max = FFMAX(x_max, img->dst_x + img->w);
+        y_max = FFMAX(y_max, img->dst_y + img->h);
+        stride_max = FFMAX(stride_max, img->dst_x + img->stride);
+    }
+
+    area->x = x_min;
+    area->y = y_min;
+    area->w = FFALIGN(x_max - x_min, 2);
+    area->h = FFALIGN(y_max - y_min, 2);
+    area->linesize[0] = area->w;    //stride_max - x_min;
+}
+
+static void ass_image_to_area_palletization(Text2GraphicSubContext *context, ASS_Image *image, AVSubtitleArea *area)
+{
+    size_t image_rgba_size;
+    uint8_t *image_rgba;
+
+    set_area_bounds(image, area);
+    av_log(context, AV_LOG_VERBOSE, "set_area_bounds %d,%d %dx%d\n", area->x, area->y, area->w, area->h);
+
+    // Create rgba image
+    image_rgba_size = (area->linesize[0] * area->h) * 4 * sizeof(uint8_t);
+    image_rgba = (uint8_t *)av_mallocz(image_rgba_size);
+    for (; image != NULL; image = image->next)
+    {
+        uint8_t rgba_color[] = {AR(image->color), AG(image->color), AB(image->color), AA(image->color)};
+        int linesize = area->linesize[0] * 4;
+        FFDrawColor color;
+        ff_draw_color(&context->draw_context, &color, rgba_color);
+        ff_blend_mask(&context->draw_context, &color,
+                      &image_rgba, &linesize, area->w, area->h,
+                      image->bitmap, image->stride, image->w, image->h,
+                      3, 0, image->dst_x - area->x, image->dst_y - area->y);
+    }
+
+    area->nb_colors = context->num_colors;
+    area->buf[0] = av_buffer_alloc(image_rgba_size / 4);
+
+    palettize_image(context->palettize_context,
+                    area->w, area->h,
+                    image_rgba, area->linesize[0] * 4,
+                    area->buf[0]->data, area->linesize[0],
+                    &area->pal[0], context->num_colors);
+
+    // Clean up
+    av_free(image_rgba);
+}
+
+static void process_header(const AVFilterContext *link, const AVFrame *frame)
+{
+    Text2GraphicSubContext *s = link->priv;
+    ASS_Track *track = s->track;
+    ASS_Style *style;
+    int sid = 0;
+
+    if (!track)
+        return;
+
+    if (frame && frame->subtitle_header) {
+        char *subtitle_header = (char *)frame->subtitle_header->data;
+        ass_process_codec_private(s->track, subtitle_header, strlen(subtitle_header));
+    }
+    else {
+        char* subtitle_header = avpriv_ass_get_subtitle_header_default(0);
+        if (!subtitle_header)
+            return;
+
+        ass_process_codec_private(s->track, subtitle_header, strlen(subtitle_header));
+        av_free(subtitle_header);
+    }
+
+    if (!s->track->event_format) {
+        s->track->event_format = av_strdup("ReadOrder, Layer, Style, Name, MarginL, MarginR, MarginV, Effect, Text");
+    }
+
+    if (s->track->n_styles == 0) {
+        sid = ass_alloc_style(track);
+        style = &s->track->styles[sid];
+        style->Name             = av_strdup("Default");
+        style->PrimaryColour    = 0xffffff00;
+        style->SecondaryColour  = 0x00ffff00;
+        style->OutlineColour    = 0x00000000;
+        style->BackColour       = 0x00000080;
+        style->Bold             = 200;
+        style->ScaleX           = 1.0;
+        style->ScaleY           = 1.0;
+        style->Spacing          = 0;
+        style->BorderStyle      = 1;
+        style->Outline          = 2;
+        style->Shadow           = 3;
+        style->Alignment        = 2;
+        track->default_style = sid;
+    }
+
+    s->got_header = 1;
+}
+
+// Main interface functions
+
+static av_cold int init(AVFilterContext *ctx)
+{
+    Text2GraphicSubContext *context = ctx->priv;
+
+    context->library = ass_library_init();
+    ass_set_message_cb(context->library, ass_log, context);
+    ass_set_fonts_dir(context->library, context->fontsdir);
+    ass_set_extract_fonts(context->library, 1);
+
+    if (context->filename) {
+        AVFormatContext *video = NULL;
+        int ret = avformat_open_input(&video, context->filename, NULL, NULL);
+        if (ret < 0) {
+            av_log(ctx, AV_LOG_ERROR, "Unable to open %s\n", context->filename);
+            return ret;
+        }
+        for (int i = 0; i < video->nb_streams; i++) {
+            const AVDictionaryEntry *tag;
+            AVStream *st = video->streams[i];
+            if (!stream_is_font(st)) continue;
+            tag = av_dict_get(st->metadata, "filename", NULL, AV_DICT_MATCH_CASE);
+            if (!tag) continue;
+            av_log(NULL, AV_LOG_DEBUG, "Loading attached font: %s\n", tag->value);
+            ass_add_font(context->library, tag->value,
+                 (char *)st->codecpar->extradata,
+                 st->codecpar->extradata_size);
+        }
+        avformat_close_input(&video);
+    }
+
+    context->renderer = ass_renderer_init(context->library);
+    ass_set_pixel_aspect(context->renderer, 1);
+    ass_set_shaper(context->renderer, 0);
+    ass_set_fonts(context->renderer, NULL, NULL, 1, NULL, 1);
+
+    context->track = ass_new_track(context->library);
+    if (!context->track) {
+        av_log(ctx, AV_LOG_ERROR, "ass_new_track() failed!\n");
+        return AVERROR(EINVAL);
+    }
+
+    ass_set_check_readorder(context->track, 0);
+
+    if (context->force_style) {
+        char **list = NULL;
+        char *temp = NULL;
+        char *ptr = av_strtok(context->force_style, ",", &temp);
+        int i = 0;
+        while (ptr) {
+            av_dynarray_add(&list, &i, ptr);
+            if (!list) {
+                return AVERROR(ENOMEM);
+            }
+            ptr = av_strtok(NULL, ",", &temp);
+        }
+        av_dynarray_add(&list, &i, NULL);
+        if (!list) {
+            return AVERROR(ENOMEM);
+        }
+        ass_set_style_overrides(context->library, list);
+        av_free(list);
+    }
+
+    init_palettizecontext(&context->palettize_context);
+
+    ff_draw_init(&context->draw_context, AV_PIX_FMT_BGRA, FF_DRAW_PROCESS_ALPHA);
+
+    return 0;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    const AVFilterContext *ctx = inlink->dst;
+    Text2GraphicSubContext *context = ctx->priv;
+    if (!context->size.width)  context->size.width  = inlink->w;
+    if (!context->size.height) context->size.height = inlink->h;
+    if (!context->size.height || !context->size.width) {
+        av_log(NULL, AV_LOG_ERROR, "A positive height and width are required to render subtitles\n");
+        return AVERROR_EXIT;
+    }
+    ass_set_frame_size(context->renderer, context->size.width, context->size.height);
+    ass_set_storage_size(context->renderer, inlink->w, inlink->h);
+
+    return 0;
+}
+
+static int config_output(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    Text2GraphicSubContext *context = ctx->priv;
+
+    outlink->w = context->size.width;
+    outlink->h = context->size.height;
+
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
+{
+    const AVFilterContext *ctx = inlink->dst;
+    Text2GraphicSubContext *context = ctx->priv;
+    AVFilterLink *outlink = ctx->outputs[0];
+    AVSubtitleArea *area;
+    int ret;
+    unsigned processed_area_cnt = 0;
+    const int64_t start_time = av_rescale_q(frame->subtitle_timing.start_pts, AV_TIME_BASE_Q, av_make_q(1, 1000));
+    const int64_t duration   = av_rescale_q(frame->subtitle_timing.duration, AV_TIME_BASE_Q, av_make_q(1, 1000));
+    ASS_Image *image;
+
+    // Postpone header processing until we receive a frame with content
+    if (!context->got_header && frame->num_subtitle_areas > 0)
+        process_header(ctx, frame);
+
+    if (frame->repeat_sub || frame->num_subtitle_areas == 0) {
+        av_frame_free(&frame);
+        return 0;
+    }
+
+    ret = av_frame_make_writable(frame);
+    if (ret < 0)
+        return ret;
+
+    if (context->stripstyles) {
+        for (unsigned r = 0; r < frame->num_subtitle_areas; r++) {
+
+            area = frame->subtitle_areas[r];
+
+            if (area->ass) {
+                char *tmp = area->ass;
+                area->ass = process_dialog(area->ass);
+
+                if (area->ass) {
+                    av_log(inlink->dst, AV_LOG_DEBUG, "original: %d %s\n", r, tmp);
+                    av_log(inlink->dst, AV_LOG_DEBUG, "stripped: %d %s\n", r, area->ass);
+                }
+
+                av_free(tmp);
+            }
+        }
+    }
+
+    for (unsigned r = 0; r < frame->num_subtitle_areas; r++)
+    {
+        area = frame->subtitle_areas[r];
+        if (area->type != AV_SUBTITLE_FMT_ASS || area->ass == NULL)
+            continue;
+
+        ass_process_chunk(context->track, area->ass, strlen(area->ass), start_time, duration);
+        processed_area_cnt++;
+
+    }
+
+    if (processed_area_cnt == 0) {
+        av_frame_free(&frame);
+        return 0;
+    }
+
+    for (unsigned r = 1; r < frame->num_subtitle_areas; r++)
+        av_free(frame->subtitle_areas[r]);
+
+    frame->num_subtitle_areas = 1;
+    area = frame->subtitle_areas[0];
+
+    image = ass_render_frame(context->renderer, context->track, start_time + duration / 2, NULL);
+    if (image == NULL) {
+        av_log(NULL, AV_LOG_WARNING, "failed to render ass: %s\n", area->ass);
+        return 0;
+    }
+
+    // TODO: Split into multiple bitmaps
+
+    ass_image_to_area_palletization(context, image, area);
+    area->type = AV_SUBTITLE_FMT_BITMAP;
+
+    av_log(NULL, AV_LOG_DEBUG, "successfully rendered ass: %s\n", area->ass);
+
+    frame->width = context->size.width;
+    frame->height = context->size.height;
+    frame->format = AV_SUBTITLE_FMT_BITMAP;
+    return ff_filter_frame(outlink, frame);
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    Text2GraphicSubContext *context = ctx->priv;
+    free_palettizecontext(&context->palettize_context);
+    if (context->track) ass_free_track(context->track);
+    if (context->renderer) ass_renderer_done(context->renderer);
+    if (context->library) ass_library_done(context->library);
+    context->track = NULL;
+    context->renderer = NULL;
+    context->library = NULL;
+}
+
+// Copied from sf_graphicsub2text, with formats swapped
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats, *formats2;
+    AVFilterLink *inlink = ctx->inputs[0];
+    AVFilterLink *outlink = ctx->outputs[0];
+    static const enum AVSubtitleType in_fmts[] = { AV_SUBTITLE_FMT_ASS, AV_SUBTITLE_FMT_NONE };
+    static const enum AVSubtitleType out_fmts[] = { AV_SUBTITLE_FMT_BITMAP, AV_SUBTITLE_FMT_NONE };
+    int ret;
+
+    /* set input format */
+    formats = ff_make_format_list(in_fmts);
+    if ((ret = ff_formats_ref(formats, &inlink->outcfg.formats)) < 0)
+        return ret;
+
+    /* set output format */
+    formats2 = ff_make_format_list(out_fmts);
+    if ((ret = ff_formats_ref(formats2, &outlink->incfg.formats)) < 0)
+        return ret;
+
+    return 0;
+}
+
+// Filter structures
+
+#define OFFSET(x) offsetof(Text2GraphicSubContext, x)
+#define FLAGS (AV_OPT_FLAG_SUBTITLE_PARAM|AV_OPT_FLAG_FILTERING_PARAM)
+
+static const AVOption text2graphicsub_options[] = {
+        { "s",           "output size",                          OFFSET(size),        AV_OPT_TYPE_IMAGE_SIZE,                         .default_val.str = NULL, .flags = FLAGS },
+        { "size",        "output size",                          OFFSET(size),        AV_OPT_TYPE_IMAGE_SIZE,                         .default_val.str = NULL, .flags = FLAGS },
+        { "n",           "number of output colors",              OFFSET(num_colors),  AV_OPT_TYPE_INT,        .min = 2, .max = 256,   .default_val.i64 = 16,   .flags = FLAGS },
+        { "num_colors",  "number of output colors",              OFFSET(num_colors),  AV_OPT_TYPE_INT,        .min = 2, .max = 256,   .default_val.i64 = 16,   .flags = FLAGS },
+        { "ss",          "strip animations and blur styles",     OFFSET(stripstyles), AV_OPT_TYPE_BOOL,       .min = 0, .max = 1,     .default_val.i64 = 1,    .flags = FLAGS },
+        { "stripstyles", "strip animations and blur styles",     OFFSET(stripstyles), AV_OPT_TYPE_BOOL,       .min = 0, .max = 1,     .default_val.i64 = 1,    .flags = FLAGS },
+        { "force_style", "enforce subtitle styles",              OFFSET(force_style), AV_OPT_TYPE_STRING,                             .default_val.str = NULL, .flags = FLAGS },
+        { "f",           "media file from which to load fonts",  OFFSET(filename),    AV_OPT_TYPE_STRING,                             .default_val.str = NULL, .flags = FLAGS },
+        { "filename",    "media file from which to load fonts",  OFFSET(filename),    AV_OPT_TYPE_STRING,                             .default_val.str = NULL, .flags = FLAGS },
+        { "fd",          "fonts directory",                      OFFSET(fontsdir),    AV_OPT_TYPE_STRING,                             .default_val.str = NULL, .flags = FLAGS },
+        { "fontsdir",    "fonts directory",                      OFFSET(fontsdir),    AV_OPT_TYPE_STRING,                             .default_val.str = NULL, .flags = FLAGS },
+        { .name =  NULL }
+};
+
+static const AVClass text2graphicsub_class = {
+        .class_name       = "text2graphicsub",
+        .item_name        = av_default_item_name,
+        .option           = text2graphicsub_options,
+        .version          = LIBAVUTIL_VERSION_INT,
+        .category         = AV_CLASS_CATEGORY_FILTER,
+};
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+        .filter_frame = filter_frame,
+        .config_props = config_input,
+    },
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+        .config_props = config_output,
+    },
+};
+
+const AVFilter ff_sf_text2graphicsub = {
+        .name            = "text2graphicsub",
+        .description     = NULL_IF_CONFIG_SMALL("Convert text subtitles to bitmap subtitles."),
+        .init            = init,
+        .uninit          = uninit,
+        .priv_size       = sizeof(Text2GraphicSubContext),
+        .priv_class      = &text2graphicsub_class,
+        FILTER_INPUTS(inputs),
+        FILTER_OUTPUTS(outputs),
+        FILTER_QUERY_FUNC(query_formats)
+};
-- 
ffmpeg-codebot

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