diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 0e752c5bf9..5a5a4be47e 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -534,6 +534,9 @@ OBJS-$(CONFIG_YUVTESTSRC_FILTER)             += vsrc_testsrc.o
 
 OBJS-$(CONFIG_NULLSINK_FILTER)               += vsink_nullsink.o
 
+# subtitle filters
+OBJS-$(CONFIG_TEXTMOD_FILTER)                += sf_textmod.o
+
 # multimedia filters
 OBJS-$(CONFIG_ABITSCOPE_FILTER)              += avf_abitscope.o
 OBJS-$(CONFIG_ADRAWGRAPH_FILTER)             += f_drawgraph.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 77463aa4c8..6d7a535ee8 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -524,6 +524,7 @@ 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_sf_textmod;
 extern const AVFilter ff_svf_graphicsub2video;
 extern const AVFilter ff_svf_textsub2video;
 
diff --git a/libavfilter/sf_textmod.c b/libavfilter/sf_textmod.c
new file mode 100644
index 0000000000..fca47d68da
--- /dev/null
+++ b/libavfilter/sf_textmod.c
@@ -0,0 +1,409 @@
+/*
+ * 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 allows to modify subtitle text in several ways
+ */
+
+#include <libavcodec/ass.h>
+
+#include "libavutil/avassert.h"
+#include "libavutil/avstring.h"
+#include "libavutil/opt.h"
+#include "avfilter.h"
+#include "internal.h"
+#include "libavcodec/avcodec.h"
+#include "libavcodec/ass_split.h"
+
+static const char* leet_src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+static const char* leet_dst = "abcd3f6#1jklmn0pq257uvwxyzAB(D3F6#1JKLMN0PQ257UVWXYZ";
+
+enum TextModOperation {
+    OP_LEET,
+    OP_TO_UPPER,
+    OP_TO_LOWER,
+    OP_REPLACE_CHARS,
+    OP_REMOVE_CHARS,
+    OP_REPLACE_WORDS,
+    OP_REMOVE_WORDS,
+    NB_OPS,
+};
+
+typedef struct TextModContext {
+    const AVClass *class;
+    enum AVSubtitleType format;
+    enum TextModOperation operation;
+    char *find;
+    char *replace;
+    char *separator;
+    char **find_list;
+    int  nb_find_list;
+    char **replace_list;
+    int  nb_replace_list;
+} TextModContext;
+
+static char **split_string(char *source, int *nb_elems, char delim)
+{
+    char **list = NULL;
+    char *temp = NULL;
+    char *ptr = av_strtok(source, &delim, &temp);
+
+    while (ptr) {
+        av_dynarray_add(&list, nb_elems, ptr);
+        if (!list)
+            return NULL;
+
+        ptr = av_strtok(NULL, &delim, &temp);
+    }
+
+    av_dynarray_add(&list, nb_elems, NULL);
+
+    return list;
+}
+
+static int init(AVFilterContext *ctx)
+{
+    TextModContext *s = ctx->priv;
+
+    switch (s->operation) {
+    case OP_REPLACE_CHARS:
+    case OP_REMOVE_CHARS:
+    case OP_REPLACE_WORDS:
+    case OP_REMOVE_WORDS:
+        if (!s->find || !strlen(s->find)) {
+            av_log(ctx, AV_LOG_ERROR, "Selected mode requires the 'find' parameter to be specified");
+            return AVERROR(EINVAL);
+        }
+        break;
+    }
+
+    switch (s->operation) {
+    case OP_REPLACE_CHARS:
+    case OP_REPLACE_WORDS:
+        if (!s->replace || !strlen(s->replace)) {
+            av_log(ctx, AV_LOG_ERROR, "Selected mode requires the 'replace' parameter to be specified");
+            return AVERROR(EINVAL);
+        }
+        break;
+    }
+
+    if (s->operation == OP_REPLACE_CHARS && strlen(s->find) != strlen(s->replace)) {
+        av_log(ctx, AV_LOG_ERROR, "Selected mode requires the 'find' and 'replace' parameters to have the same length");
+        return AVERROR(EINVAL);
+    }
+
+    if (s->operation == OP_REPLACE_WORDS || s->operation == OP_REMOVE_WORDS) {
+        if (!s->separator || strlen(s->separator) != 1) {
+            av_log(ctx, AV_LOG_ERROR, "Selected mode requires a single separator char to be specified");
+            return AVERROR(EINVAL);
+        }
+
+        s->find_list = split_string(s->find, &s->nb_find_list, *s->separator);
+        if (!s->find_list)
+            return AVERROR(ENOMEM);
+
+        if (s->operation == OP_REPLACE_WORDS) {
+
+            s->replace_list = split_string(s->replace, &s->nb_replace_list, *s->separator);
+            if (!s->replace_list)
+                return AVERROR(ENOMEM);
+
+            if (s->nb_find_list != s->nb_replace_list) {
+                av_log(ctx, AV_LOG_ERROR, "The number of words in 'find' and 'replace' needs to be equal");
+                return AVERROR(EINVAL);
+            }
+        }
+    }
+
+    return 0;
+}
+
+static void uninit(AVFilterContext *ctx)
+{
+    TextModContext *s = ctx->priv;
+    int i;
+
+    for (i = 0; i < s->nb_find_list; i++) {
+        av_free(&s->find_list[i]);
+    }
+    s->nb_find_list = 0;
+    av_freep(&s->find_list);
+
+    for (i = 0; i < s->nb_replace_list; i++) {
+        av_free(&s->replace_list[i]);
+    }
+    s->nb_replace_list = 0;
+    av_freep(&s->replace_list);
+}
+
+static int 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_ASS, AV_SUBTITLE_FMT_NONE };
+    int ret;
+
+    /* set input subtitle format */
+    formats = ff_make_format_list(subtitle_fmts);
+    if ((ret = ff_formats_ref(formats, &inlink->outcfg.formats)) < 0)
+        return ret;
+
+    /* set output video format */
+    if ((ret = ff_formats_ref(formats, &outlink->incfg.formats)) < 0)
+        return ret;
+
+    return 0;
+}
+
+static char *process_text(TextModContext *s, char *text)
+{
+    const char *char_src = s->find;
+    const char *char_dst = s->replace;
+    char *result = NULL;
+    int escape_level = 0, k = 0;
+
+    switch (s->operation) {
+    case OP_LEET:
+    case OP_REPLACE_CHARS:
+
+        if (s->operation == OP_LEET) {
+            char_src = leet_src;
+            char_dst = leet_dst;
+        }
+
+        result = av_strdup(text);
+        if (!result)
+            return NULL;
+
+        for (size_t n = 0; n < strlen(result); n++) {
+            if (result[n] == '{')
+                escape_level++;
+
+            if (!escape_level) {
+                for (size_t t = 0; t < FF_ARRAY_ELEMS(char_src); t++) {
+                    if (result[n] == char_src[t]) {
+                        result[n] = char_dst[t];
+                        break;
+                    }
+                }
+            }
+
+            if (result[n] == '}')
+                escape_level--;
+        }
+
+        break;
+    case OP_TO_UPPER:
+    case OP_TO_LOWER:
+
+        result = av_strdup(text);
+        if (!result)
+            return NULL;
+
+        for (size_t n = 0; n < strlen(result); n++) {
+            if (result[n] == '{')
+                escape_level++;
+            if (!escape_level)
+                result[n] = s->operation == OP_TO_LOWER ? av_tolower(result[n]) : av_toupper(result[n]);
+            if (result[n] == '}')
+                escape_level--;
+        }
+
+        break;
+    case OP_REMOVE_CHARS:
+
+        result = av_strdup(text);
+        if (!result)
+            return NULL;
+
+        for (size_t n = 0; n < strlen(result); n++) {
+            int skip_char = 0;
+
+            if (result[n] == '{')
+                escape_level++;
+
+            if (!escape_level) {
+                for (size_t t = 0; t < FF_ARRAY_ELEMS(char_src); t++) {
+                    if (result[n] == char_src[t]) {
+                        skip_char = 1;
+                        break;
+                    }
+                }
+            }
+
+            if (!skip_char)
+                result[k++] = result[n];
+
+            if (result[n] == '}')
+                escape_level--;
+        }
+
+        result[k] = 0;
+
+        break;
+    case OP_REPLACE_WORDS:
+    case OP_REMOVE_WORDS:
+
+        result = av_strdup(text);
+        if (!result)
+            return NULL;
+
+        for (int n = 0; n < s->nb_find_list; n++) {
+            char *tmp           = result;
+            const char *replace = (s->operation == OP_REPLACE_WORDS) ? s->replace_list[n] : "";
+
+            result = av_strireplace(result, s->find_list[n], replace);
+            if (!result)
+                return NULL;
+
+            av_free(tmp);
+        }
+
+        break;
+    }
+
+    return result;
+}
+
+static char *process_dialog(TextModContext *s, char *ass_line)
+{
+    ASSDialog *dialog = ff_ass_split_dialog(NULL, ass_line);
+    char *result, *text;
+
+    if (!dialog)
+        return NULL;
+
+    text = process_text(s, dialog->text);
+    if (!text)
+        return NULL;
+
+    result = ff_ass_get_dialog(dialog->readorder, dialog->layer, dialog->style, dialog->name, text);
+
+    av_free(text);
+    ff_ass_free_dialog(&dialog);
+    return result;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *src_frame)
+{
+    TextModContext *s = inlink->dst->priv;
+    AVFilterLink *outlink = inlink->dst->outputs[0];
+    AVSubtitle *sub;
+    int ret;
+    AVFrame *out;
+
+    outlink->format = inlink->format;
+
+    out = av_frame_alloc();
+    if (!out) {
+        av_frame_free(&src_frame);
+        return AVERROR(ENOMEM);
+    }
+
+    out->format = outlink->format;
+
+    if ((ret = av_frame_get_buffer2(out, AVMEDIA_TYPE_SUBTITLE, 0)) < 0)
+        return ret;
+
+    out->pts                    = src_frame->pts;
+    out->pkt_dts                = src_frame->pkt_dts;
+    out->pkt_duration           = src_frame->pkt_duration;
+    out->best_effort_timestamp  = src_frame->best_effort_timestamp;
+
+    sub = (AVSubtitle *)src_frame->data[0];
+
+    if (sub) {
+        AVSubtitle *out_sub = av_memdup(sub, sizeof(*out_sub));
+        if (!out_sub)
+            return AVERROR(ENOMEM);
+
+        out->buf[0] = av_buffer_create((uint8_t*)out_sub, sizeof(*out_sub), avsubtitle_free_ref, NULL, AV_BUFFER_FLAG_READONLY);
+        out->data[0] = (uint8_t*)out_sub;
+
+        if (sub->num_rects) {
+            out_sub->rects = av_malloc_array(sub->num_rects, sizeof(AVSubtitleRect *));
+        }
+
+        for (unsigned i = 0; i < sub->num_rects; i++) {
+
+            const AVSubtitleRect *src_rect = sub->rects[i];
+            AVSubtitleRect *dst_rect = av_memdup(src_rect, sizeof(*dst_rect));
+            out_sub->rects[i] = dst_rect;
+
+            if (src_rect->ass) {
+                dst_rect->ass = process_dialog(s, src_rect->ass);
+                if (!dst_rect->ass)
+                    return AVERROR(ENOMEM);
+            }
+        }
+    }
+
+    av_frame_free(&src_frame);
+    return ff_filter_frame(outlink, out);
+}
+
+#define OFFSET(x) offsetof(TextModContext, x)
+#define FLAGS (AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_FILTERING_PARAM)
+
+static const AVOption textmod_options[] = {
+    { "mode",             "set operation mode",              OFFSET(operation),  AV_OPT_TYPE_INT,    {.i64=OP_LEET},          OP_LEET, NB_OPS-1, FLAGS, "mode" },
+    {   "leet",           "convert text to 'leet speak'",    0,                  AV_OPT_TYPE_CONST,  {.i64=OP_LEET},          0,       0,        FLAGS, "mode" },
+    {   "to_upper",       "change to upper case",            0,                  AV_OPT_TYPE_CONST,  {.i64=OP_TO_UPPER},      0,       0,        FLAGS, "mode" },
+    {   "to_lower",       "change to lower case",            0,                  AV_OPT_TYPE_CONST,  {.i64=OP_TO_LOWER},      0,       0,        FLAGS, "mode" },
+    {   "replace_chars",  "replace characters",              0,                  AV_OPT_TYPE_CONST,  {.i64=OP_REPLACE_CHARS}, 0,       0,        FLAGS, "mode" },
+    {   "remove_chars",   "remove characters",               0,                  AV_OPT_TYPE_CONST,  {.i64=OP_REMOVE_CHARS},  0,       0,        FLAGS, "mode" },
+    {   "replace_words",  "replace words",                   0,                  AV_OPT_TYPE_CONST,  {.i64=OP_REPLACE_WORDS}, 0,       0,        FLAGS, "mode" },
+    {   "remove_words",   "remove words",                    0,                  AV_OPT_TYPE_CONST,  {.i64=OP_REMOVE_WORDS},  0,       0,        FLAGS, "mode" },
+    { "find",             "chars/words to find or remove",   OFFSET(find),       AV_OPT_TYPE_STRING, {.str = NULL},           0,       0,        FLAGS, NULL   },
+    { "replace",          "chars/words to replace",          OFFSET(replace),    AV_OPT_TYPE_STRING, {.str = NULL},           0,       0,        FLAGS, NULL   },
+    { "separator",        "word separator (default: ',')",   OFFSET(separator),  AV_OPT_TYPE_STRING, {.str = ","},            0,       0,        FLAGS, NULL   },
+    { NULL },
+};
+
+AVFILTER_DEFINE_CLASS(textmod);
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_SUBTITLE,
+        .filter_frame = filter_frame,
+    },
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_SUBTITLE,
+    },
+};
+
+const AVFilter ff_sf_textmod = {
+    .name          = "textmod",
+    .description   = NULL_IF_CONFIG_SMALL("Modify subtitle text in several ways"),
+    .init          = init,
+    .uninit        = uninit,
+    .query_formats = query_formats,
+    .priv_size     = sizeof(TextModContext),
+    .priv_class    = &textmod_class,
+    FILTER_INPUTS(inputs),
+    FILTER_OUTPUTS(outputs),
+};
