[FFmpeg-devel] [PATCH v9 16/25] avfilter/stripstyles: Add stripstyles filter

[softworkz <ffmpegagent@gmail.com>]

From: softworkz <softworkz@hotmail.com>

- stripstyles {S -> S)
  Remove all inline styles from subtitle events

Signed-off-by: softworkz <softworkz@hotmail.com>
---
 doc/filters.texi             |  37 ++++++
 libavfilter/Makefile         |   1 +
 libavfilter/allfilters.c     |   1 +
 libavfilter/sf_stripstyles.c | 237 +++++++++++++++++++++++++++++++++++
 4 files changed, 276 insertions(+)
 create mode 100644 libavfilter/sf_stripstyles.c

diff --git a/doc/filters.texi b/doc/filters.texi
index 1f7989e92f..383e020c8d 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -27432,6 +27432,43 @@ ffmpeg -i "http://streams.videolan.org/samples/sub/SSA/subtitle_testing_complex.
 @end example
 @end itemize
 
+@section stripstyles
+
+Remove all inline styles from subtitle events.
+
+Inputs:
+@itemize
+@item 0: Subtitles[TEXT]
+@end itemize
+
+Outputs:
+@itemize
+@item 0: Subtitles[TEXT]
+@end itemize
+
+It accepts the following parameters:
+
+@table @option
+@item remove_animated
+Also remove text which is subject to animation (default: true)
+Usually, animated text elements are used used in addition to static subtitle lines for creating effects, so in most cases it is safe to remove the animation content.
+If subtitle text is missing, try setting this to false.
+
+@item select_layer
+Process only ASS subtitle events from a specific layer. This allows to filter out certain effects where an ASS author duplicates the text onto multiple layers.
+
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Remove styles and animations from ASS subtitles and output events from ass layer 0 only. Then convert asn save as SRT stream:
+@example
+ffmpeg -i "https://streams.videolan.org/samples/sub/SSA/subtitle_testing_complex.mkv" -filter_complex "[0:1]stripstyles=select_layer=0" -map 0 -c:s srt output.mkv
+@end example
+@end itemize
+
 
 @section textmod
 
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 5d82b3e8c4..01b7440cce 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -590,6 +590,7 @@ OBJS-$(CONFIG_NULLSINK_FILTER)               += vsink_nullsink.o
 # subtitle filters
 OBJS-$(CONFIG_CENSOR_FILTER)                 += sf_textmod.o
 OBJS-$(CONFIG_SHOW_SPEAKER_FILTER)           += sf_textmod.o
+OBJS-$(CONFIG_STRIPSTYLES_FILTER)            += sf_stripstyles.o
 OBJS-$(CONFIG_TEXTMOD_FILTER)                += sf_textmod.o
 
 # multimedia filters
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index d7f24ab7db..33bfae7358 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -578,6 +578,7 @@ extern const AVFilter ff_avsrc_movie;
 /* subtitle filters */
 extern const AVFilter ff_sf_censor;
 extern const AVFilter ff_sf_showspeaker;
+extern const AVFilter ff_sf_stripstyles;
 extern const AVFilter ff_sf_textmod;
 
 /* those filters are part of public or internal API,
diff --git a/libavfilter/sf_stripstyles.c b/libavfilter/sf_stripstyles.c
new file mode 100644
index 0000000000..78dc6f3ef4
--- /dev/null
+++ b/libavfilter/sf_stripstyles.c
@@ -0,0 +1,237 @@
+/*
+ * Copyright (c) 2021 softworkz
+ *
+ * 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
+ * text subtitle filter which removes inline-styles from subtitles
+ */
+
+#include "libavutil/opt.h"
+#include "internal.h"
+#include "libavutil/ass_internal.h"
+#include "libavutil/ass_split_internal.h"
+#include "libavutil/bprint.h"
+
+typedef struct StripStylesContext {
+    const AVClass *class;
+    enum AVSubtitleType format;
+    int remove_animated;
+    enum ASSSplitComponents keep_flags;
+    int select_layer;
+} StripStylesContext;
+
+typedef struct DialogContext {
+    StripStylesContext* ss_ctx;
+    AVBPrint buffer;
+    int drawing_scale;
+    int is_animated;
+    int plain_text_length;
+} DialogContext;
+
+static void dialog_text_cb(void *priv, const char *text, int len)
+{
+    DialogContext *s = priv;
+
+    av_log(s->ss_ctx, AV_LOG_DEBUG, "dialog_text_cb: %s\n", text);
+
+    if (!s->drawing_scale && (!s->is_animated || !s->ss_ctx->remove_animated))
+        s->plain_text_length += len;
+        ////av_bprint_append_data(&s->buffer, text, len);
+}
+
+static void dialog_new_line_cb(void *priv, int forced)
+{
+    DialogContext *s = priv;
+    if (!s->drawing_scale && !s->is_animated)
+        s->plain_text_length += 2;
+        ////av_bprint_append_data(&s->buffer, forced ? "\\N" : "\\n", 2);
+}
+
+static void dialog_drawing_mode_cb(void *priv, int scale)
+{
+    DialogContext *s = priv;
+    s->drawing_scale = scale;
+}
+
+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,
+    .new_line         = dialog_new_line_cb,
+    .drawing_mode     = dialog_drawing_mode_cb,
+    .animate          = dialog_animate_cb,
+    .move             = dialog_move_cb,
+};
+
+static char *process_dialog(StripStylesContext *s, const char *ass_line)
+{
+    DialogContext dlg_ctx = { .ss_ctx = s };
+    ASSDialog *dialog = avpriv_ass_split_dialog(NULL, ass_line);
+    char *result = NULL;
+
+    if (!dialog)
+        return NULL;
+
+    if (s->select_layer >= 0 && dialog->layer != s->select_layer) {
+        avpriv_ass_free_dialog(&dialog);
+        return NULL;
+    }
+
+    dlg_ctx.ss_ctx = s;
+
+    av_bprint_init(&dlg_ctx.buffer, 512, AV_BPRINT_SIZE_UNLIMITED);
+
+    avpriv_ass_filter_override_codes(&dialog_callbacks, &dlg_ctx, dialog->text, &dlg_ctx.buffer, s->keep_flags);
+
+    if (av_bprint_is_complete(&dlg_ctx.buffer) && dlg_ctx.buffer.len > 0 && dlg_ctx.plain_text_length > 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, dlg_ctx.buffer.str);
+
+    av_bprint_finalize(&dlg_ctx.buffer, NULL);
+    avpriv_ass_free_dialog(&dialog);
+
+    return result;
+}
+
+static int config_output(AVFilterLink *outlink)
+{
+    AVFilterLink *inlink = outlink->src->inputs[0];
+
+    outlink->w = inlink->w;
+    outlink->h = inlink->h;
+    outlink->time_base = inlink->time_base;
+    outlink->frame_rate = inlink->frame_rate;
+
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
+{
+    StripStylesContext *s = inlink->dst->priv;
+    AVFilterLink *outlink = inlink->dst->outputs[0];
+    int ret;
+
+    outlink->format = inlink->format;
+
+    ret = av_frame_make_writable(frame);
+    if (ret <0 ) {
+        av_frame_free(&frame);
+        return AVERROR(ENOMEM);
+    }
+
+    for (unsigned i = 0; i < frame->num_subtitle_areas; i++) {
+
+        AVSubtitleArea *area = frame->subtitle_areas[i];
+
+        if (area->ass) {
+            char *tmp = area->ass;
+            area->ass = process_dialog(s, area->ass);
+
+            if (area->ass) {
+                av_log(inlink->dst, AV_LOG_DEBUG, "original: %d %s\n", i, tmp);
+                av_log(inlink->dst, AV_LOG_DEBUG, "stripped: %d %s\n", i, area->ass);
+            }
+            else
+                area->ass = NULL;
+
+            av_free(tmp);
+        }
+    }
+
+    return ff_filter_frame(outlink, frame);
+}
+
+#define OFFSET(x) offsetof(StripStylesContext, x)
+#define FLAGS (AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_FILTERING_PARAM)
+
+static const AVOption stripstyles_options[] = {
+    { "keep_flags", "flags to control which override codes to keep", OFFSET(keep_flags), AV_OPT_TYPE_FLAGS, { .i64 = ASS_SPLIT_TEXT }, .flags = FLAGS, .unit = "keepflags" },
+        { "basic",          "keep static style tags only",             .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_BASIC          },  .flags=FLAGS, .unit = "keepflags" },
+        { "all_known",      "keep all known tags",                     .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_ALL_KNOWN      },  .flags=FLAGS, .unit = "keepflags" },
+        { "text",           "keep text content",                       .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT           },  .flags=FLAGS, .unit = "keepflags" },
+        { "color",          "keep color tags (\\c, \\<n>c)",           .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_COLOR          },  .flags=FLAGS, .unit = "keepflags" },
+        { "alpha",          "keep color alpha tags (\\alpha, \\<n>a)", .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_ALPHA          },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_name",      "keep font name tags (\\fn)",              .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_NAME      },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_size",      "keep font size tags (\\fs)",              .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_SIZE      },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_scale",     "keep font scale tags (\\fscx, \\fscy)",   .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_SCALE     },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_spacing",   "keep font spacing tags (\\fsp)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_SPACING   },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_charset",   "keep font charset tags (\\fe)",           .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_CHARSET   },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_bold",      "keep font bold tags (\\b)",               .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_BOLD      },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_italic",    "keep font italic tags (\\i)",             .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_ITALIC    },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_underline", "keep font underline tags (\\u)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_UNDERLINE },  .flags=FLAGS, .unit = "keepflags" },
+        { "font_strikeout", "keep font strikeout tags (\\s)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FONT_STRIKEOUT },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_border",    "keep text border tags (\\bord)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_BORDER    },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_shadow",    "keep text shadow tags (\\shad)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_SHADOW    },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_rotate",    "keep text rotate tags (\\fr)",            .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_ROTATE    },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_blur",      "keep text blur tags (\\blur, \\be)",      .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_BLUR      },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_wrap",      "keep text wrap tags (\\q)",               .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_WRAP      },  .flags=FLAGS, .unit = "keepflags" },
+        { "text_align",     "keep text align tags (\\a, \\an)",        .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_TEXT_ALIGNMENT },  .flags=FLAGS, .unit = "keepflags" },
+        { "reset_override", "keep override reset tags (\\r)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_CANCELLING     },  .flags=FLAGS, .unit = "keepflags" },
+        { "move",           "keep move tags (\\move)",                 .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_MOVE           },  .flags=FLAGS, .unit = "keepflags" },
+        { "pos",            "keep position tags (\\pos)",              .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_POS            },  .flags=FLAGS, .unit = "keepflags" },
+        { "origin",         "keep origin tags (\\org)",                .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_ORIGIN         },  .flags=FLAGS, .unit = "keepflags" },
+        { "draw",           "keep drawing tags (\\p)",                 .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_DRAW           },  .flags=FLAGS, .unit = "keepflags" },
+        { "animate",        "keep animation tags (\\t)",               .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_ANIMATE        },  .flags=FLAGS, .unit = "keepflags" },
+        { "fade",           "keep fade tags (\\fad, \\fade)",          .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_FADE           },  .flags=FLAGS, .unit = "keepflags" },
+        { "clip",           "keep clip tags (\\clip)",                 .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_CLIP           },  .flags=FLAGS, .unit = "keepflags" },
+        { "unknown",        "keep unknown tags",                       .type = AV_OPT_TYPE_CONST, { .i64 = ASS_SPLIT_UNKNOWN        },  .flags=FLAGS, .unit = "keepflags" },
+    { "remove_animated", "remove animated text (default: yes)",   OFFSET(remove_animated),  AV_OPT_TYPE_BOOL, {.i64 = 1 },  0, 1, FLAGS, 0 },
+    { "select_layer", "process a specific ass layer only",   OFFSET(select_layer),  AV_OPT_TYPE_INT, {.i64 = -1 }, -1, INT_MAX, FLAGS, 0 },
+    { NULL },
+};
+
+AVFILTER_DEFINE_CLASS(stripstyles);
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+        .filter_frame = filter_frame,
+    },
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_SUBTITLE,
+        .config_props  = config_output,
+    },
+};
+
+const AVFilter ff_sf_stripstyles = {
+    .name          = "stripstyles",
+    .description   = NULL_IF_CONFIG_SMALL("Strip subtitle inline styles"),
+    .priv_size     = sizeof(StripStylesContext),
+    .priv_class    = &stripstyles_class,
+    FILTER_INPUTS(inputs),
+    FILTER_OUTPUTS(outputs),
+    FILTER_SINGLE_SUBFMT(AV_SUBTITLE_FMT_ASS),
+};
+
-- 
ffmpeg-codebot

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