[FFmpeg-devel] [PATCH v14 13/14] avfilter/graphicsub2text: Add new graphicsub2text filter (OCR)
Soft Works
softworkz at hotmail.com
Thu Oct 21 06:19:55 EEST 2021
Signed-off-by: softworkz <softworkz at hotmail.com>
---
configure | 1 +
doc/filters.texi | 55 ++++++
libavfilter/Makefile | 2 +
libavfilter/allfilters.c | 1 +
libavfilter/sf_graphicsub2text.c | 323 +++++++++++++++++++++++++++++++
5 files changed, 382 insertions(+)
create mode 100644 libavfilter/sf_graphicsub2text.c
diff --git a/configure b/configure
index 31092ab38b..3276264c0c 100755
--- a/configure
+++ b/configure
@@ -3605,6 +3605,7 @@ frei0r_deps_any="libdl LoadLibrary"
frei0r_filter_deps="frei0r"
frei0r_src_filter_deps="frei0r"
fspp_filter_deps="gpl"
+graphicsub2text_filter_deps="libtesseract"
histeq_filter_deps="gpl"
hqdn3d_filter_deps="gpl"
interlace_filter_deps="gpl"
diff --git a/doc/filters.texi b/doc/filters.texi
index 7f7ccc3f2a..e75d095ea4 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -25502,6 +25502,61 @@ ffmpeg -i "https://streams.videolan.org/ffmpeg/mkv_subtitles.mkv" -filter_comple
@end example
@end itemize
+ at section graphicsub2text
+
+Converts graphic subtitles to text subtitles by performing OCR.
+
+For this filter to be available, ffmpeg needs to be compiled with libtesseract (see https://github.com/tesseract-ocr/tesseract).
+Language models need to be downloaded from https://github.com/tesseract-ocr/tessdata and put into as subfolder named 'tessdata' or into a folder specified via the environment variable 'TESSDATA_PREFIX'.
+The path can also be specified via filter option (see below).
+
+Note: These models are including the data for both OCR modes.
+
+Inputs:
+- 0: Subtitles [bitmap]
+
+Outputs:
+- 0: Subtitles [text]
+
+It accepts the following parameters:
+
+ at table @option
+ at item ocr_mode
+The character recognition mode to use.
+
+Supported OCR modes are:
+
+ at table @var
+ at item 0, tesseract
+This is the classic libtesseract operation mode. It is fast but less accurate than LSTM.
+ at item 1, lstm
+Newer OCR implementation based on ML models. Provides usually better results, requires more processing resources.
+ at item 2, both
+Use a combination of both modes.
+ at end table
+
+ at item tessdata_path
+The path to a folder containing the language models to be used.
+
+ at item language
+The recognition language. It needs to match the first three characters of a language model file in the tessdata path.
+
+ at end table
+
+
+ at subsection Examples
+
+ at itemize
+ at item
+Convert DVB graphic subtitles to ASS (text) subtitles
+
+Note: For this to work, you need to have the data file 'eng.traineddata' in a 'tessdata' subfolder (see above).
+ at example
+ffmpeg ffmpeg -loglevel verbose -i "https://streams.videolan.org/streams/ts/video_subs_ttxt%2Bdvbsub.ts" -filter_complex "[0:13]graphicsub2text=ocr_mode=both" -c:s ass -y output.mkv
+ at end example
+ at end itemize
+
+
@section graphicsub2video
Renders graphic subtitles as video frames.
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 302bdaf416..6e5b04c250 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -293,6 +293,8 @@ OBJS-$(CONFIG_GBLUR_FILTER) += vf_gblur.o
OBJS-$(CONFIG_GEQ_FILTER) += vf_geq.o
OBJS-$(CONFIG_GRADFUN_FILTER) += vf_gradfun.o
OBJS-$(CONFIG_GRAPHICSUB2VIDEO_FILTER) += vf_overlaygraphicsubs.o framesync.o
+OBJS-$(CONFIG_GRAPHICSUB2TEXT_FILTER) += sf_graphicsub2text.o
+OBJS-$(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
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index f0eccbacd4..70399a77f4 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -535,6 +535,7 @@ extern const AVFilter ff_avf_showwaves;
extern const AVFilter ff_avf_showwavespic;
extern const AVFilter ff_vaf_spectrumsynth;
extern const AVFilter ff_sf_censor;
+extern const AVFilter ff_sf_graphicsub2text;
extern const AVFilter ff_sf_showspeaker;
extern const AVFilter ff_sf_splitcc;
extern const AVFilter ff_sf_stripstyles;
diff --git a/libavfilter/sf_graphicsub2text.c b/libavfilter/sf_graphicsub2text.c
new file mode 100644
index 0000000000..c963ba4384
--- /dev/null
+++ b/libavfilter/sf_graphicsub2text.c
@@ -0,0 +1,323 @@
+/*
+ * 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
+ * subtitle filter to convert graphical subs to text subs via OCR
+ */
+
+#include <tesseract/capi.h>
+#include <libavutil/ass_internal.h>
+
+#include "libavutil/opt.h"
+#include "subtitles.h"
+
+typedef struct SubOcrContext {
+ const AVClass *class;
+ int w, h;
+
+ TessBaseAPI *tapi;
+ TessOcrEngineMode ocr_mode;
+ char *tessdata_path;
+ char *language;
+
+ int readorder_counter;
+
+ AVFrame *pending_frame;
+} SubOcrContext;
+
+
+static int init(AVFilterContext *ctx)
+{
+ SubOcrContext *s = ctx->priv;
+ const char* tver = TessVersion();
+ int ret;
+
+ s->tapi = TessBaseAPICreate();
+
+ if (!s->tapi || !tver || !strlen(tver)) {
+ av_log(ctx, AV_LOG_ERROR, "Failed to access libtesseract\n");
+ return AVERROR(ENOSYS);
+ }
+
+ av_log(ctx, AV_LOG_VERBOSE, "Initializing libtesseract, version: %s\n", tver);
+
+ ret = TessBaseAPIInit4(s->tapi, s->tessdata_path, s->language, s->ocr_mode, NULL, 0, NULL, NULL, 0, 1);
+ if (ret < 0 ) {
+ av_log(ctx, AV_LOG_ERROR, "Failed to initialize libtesseract. Error: %d\n", ret);
+ return AVERROR(ENOSYS);
+ }
+
+ ret = TessBaseAPISetVariable(s->tapi, "tessedit_char_blacklist", "|");
+ if (ret < 0 ) {
+ av_log(ctx, AV_LOG_ERROR, "Failed to set 'tessedit_char_blacklist'. Error: %d\n", ret);
+ return AVERROR(EINVAL);
+ }
+
+ return 0;
+}
+
+static void uninit(AVFilterContext *ctx)
+{
+ SubOcrContext *s = ctx->priv;
+
+ if (s->tapi) {
+ TessBaseAPIEnd(s->tapi);
+ TessBaseAPIDelete(s->tapi);
+ }
+}
+
+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_BITMAP, AV_SUBTITLE_FMT_NONE };
+ static const enum AVSubtitleType out_fmts[] = { AV_SUBTITLE_FMT_ASS, 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;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+ AVFilterContext *ctx = inlink->dst;
+ SubOcrContext *s = ctx->priv;
+
+ if (s->w <= 0 || s->h <= 0) {
+ s->w = inlink->w;
+ s->h = inlink->h;
+ }
+ return 0;
+}
+
+static int config_output(AVFilterLink *outlink)
+{
+ const AVFilterContext *ctx = outlink->src;
+ SubOcrContext *s = ctx->priv;
+
+ outlink->format = AV_SUBTITLE_FMT_ASS;
+ outlink->w = s->w;
+ outlink->h = s->h;
+
+ return 0;
+}
+
+static uint8_t* create_grayscale_image(AVFilterContext *ctx, AVSubtitleArea *area)
+{
+ uint8_t gray_pal[256];
+ const size_t img_size = area->buf[0]->size;
+ const uint8_t* img = area->buf[0]->data;
+ uint8_t* gs_img = av_malloc(img_size);
+
+ if (!gs_img)
+ return NULL;
+
+ for (unsigned i = 0; i < 256; i++) {
+ const uint8_t *col = (uint8_t*)&area->pal[i];
+ const int val = (int)col[3] * FFMAX3(col[0], col[1], col[2]);
+ gray_pal[i] = (uint8_t)(val >> 8);
+ }
+
+ for (unsigned i = 0; i < img_size; i++)
+ gs_img[i] = 255 - gray_pal[img[i]];
+
+ return gs_img;
+}
+
+static int convert_area(AVFilterContext *ctx, AVSubtitleArea *area)
+{
+ SubOcrContext *s = ctx->priv;
+ char *ocr_text = NULL;
+ int ret;
+ uint8_t *gs_img = create_grayscale_image(ctx, area);
+
+ if (!gs_img)
+ return AVERROR(ENOMEM);
+
+ area->type = AV_SUBTITLE_FMT_ASS;
+ TessBaseAPISetImage(s->tapi, gs_img, area->w, area->h, 1, area->linesize[0]);
+ TessBaseAPISetSourceResolution(s->tapi, 70);
+
+ ret = TessBaseAPIRecognize(s->tapi, NULL);
+ if (ret == 0)
+ ocr_text = TessBaseAPIGetUTF8Text(s->tapi);
+
+ if (!ocr_text) {
+ av_log(ctx, AV_LOG_WARNING, "OCR didn't return a text. ret=%d\n", ret);
+ area->ass = NULL;
+ }
+ else {
+ const size_t len = strlen(ocr_text);
+
+ if (len > 0 && ocr_text[len - 1] == '\n')
+ ocr_text[len - 1] = 0;
+
+ av_log(ctx, AV_LOG_VERBOSE, "OCR Result: %s\n", ocr_text);
+
+ area->ass = av_strdup(ocr_text);
+
+ TessDeleteText(ocr_text);
+ }
+
+ av_freep(&gs_img);
+ av_buffer_unref(&area->buf[0]);
+ area->type = AV_SUBTITLE_FMT_ASS;
+
+ return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
+{
+ AVFilterContext *ctx = inlink->dst;
+ SubOcrContext *s = ctx->priv;
+ AVFilterLink *outlink = inlink->dst->outputs[0];
+ int ret, frame_sent = 0;
+
+ if (s->pending_frame) {
+ const uint64_t pts_diff = frame->subtitle_pts - s->pending_frame->subtitle_pts;
+ s->pending_frame->subtitle_end_time = (uint32_t)(pts_diff / 1000);
+
+ ret = ff_filter_frame(outlink, s->pending_frame);
+ s->pending_frame = NULL;
+ if (ret < 0)
+ return ret;
+
+ frame_sent = 1;
+
+ if (frame->num_subtitle_areas == 0) {
+ // No need to forward this empty frame
+ av_frame_free(&frame);
+ return 0;
+ }
+ }
+
+ ret = av_frame_make_writable(frame);
+
+ if (ret < 0) {
+ av_frame_free(&frame);
+ return ret;
+ }
+
+ frame->format = AV_SUBTITLE_FMT_ASS;
+
+ av_log(ctx, AV_LOG_DEBUG, "filter_frame sub_pts: %"PRIu64", start_time: %d, end_time: %d, num_areas: %d\n",
+ frame->subtitle_pts, frame->subtitle_start_time, frame->subtitle_end_time, frame->num_subtitle_areas);
+
+ if (frame->num_subtitle_areas > 1 &&
+ frame->subtitle_areas[0]->y > frame->subtitle_areas[frame->num_subtitle_areas - 1]->y) {
+
+ for (unsigned i = 0; i < frame->num_subtitle_areas / 2; i++)
+ FFSWAP(AVSubtitleArea*, frame->subtitle_areas[i], frame->subtitle_areas[frame->num_subtitle_areas - i - 1]);
+ }
+
+ for (unsigned i = 0; i < frame->num_subtitle_areas; i++) {
+ AVSubtitleArea *area = frame->subtitle_areas[i];
+
+ ret = convert_area(ctx, area);
+ if (ret < 0)
+ return ret;
+
+ if (area->ass && area->ass[0] != '\0') {
+ char *tmp = area->ass;
+
+ if (i == 0)
+ area->ass = avpriv_ass_get_dialog(s->readorder_counter++, 0, "Default", NULL, tmp);
+ else
+ area->ass = av_asprintf("\\N%s", tmp);
+
+ av_free(tmp);
+ }
+ }
+
+ // When decoders can't determine the end time, they are setting it either to UINT32_NAX
+ // or 30s (dvbsub).
+ if (frame->num_subtitle_areas > 0 && frame->subtitle_end_time >= 30000) {
+ // Can't send it without end time, wait for the next frame to determine the end_display time
+ s->pending_frame = frame;
+
+ if (frame_sent)
+ return 0;
+
+ // To keep all going, send an empty frame instead
+ frame = ff_get_subtitles_buffer(outlink, AV_SUBTITLE_FMT_ASS);
+ if (!frame)
+ return AVERROR(ENOMEM);
+
+ av_frame_copy_props(frame, s->pending_frame);
+ frame->subtitle_end_time = 1;
+ }
+
+ return ff_filter_frame(outlink, frame);
+}
+
+#define OFFSET(x) offsetof(SubOcrContext, x)
+#define FLAGS (AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_FILTERING_PARAM)
+
+static const AVOption graphicsub2text_options[] = {
+ { "ocr_mode", "set ocr mode", OFFSET(ocr_mode), AV_OPT_TYPE_INT, {.i64=OEM_TESSERACT_ONLY}, OEM_TESSERACT_ONLY, 2, FLAGS, "ocr_mode" },
+ { "tesseract", "classic tesseract ocr", 0, AV_OPT_TYPE_CONST, {.i64=OEM_TESSERACT_ONLY}, 0, 0, FLAGS, "ocr_mode" },
+ { "lstm", "lstm (ML based)", 0, AV_OPT_TYPE_CONST, {.i64=OEM_LSTM_ONLY}, 0, 0, FLAGS, "ocr_mode" },
+ { "both", "use both models combined", 0, AV_OPT_TYPE_CONST, {.i64=OEM_TESSERACT_LSTM_COMBINED}, 0, 0, FLAGS, "ocr_mode" },
+ { "tessdata_path", "path to tesseract data", OFFSET(tessdata_path), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS, NULL },
+ { "language", "ocr language", OFFSET(language), AV_OPT_TYPE_STRING, {.str = "eng"}, 0, 0, FLAGS, NULL },
+ { NULL },
+};
+
+AVFILTER_DEFINE_CLASS(graphicsub2text);
+
+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_graphicsub2text = {
+ .name = "graphicsub2text",
+ .description = NULL_IF_CONFIG_SMALL("Convert graphical subtitles to text subtitles via OCR"),
+ .init = init,
+ .uninit = uninit,
+ .priv_size = sizeof(SubOcrContext),
+ .priv_class = &graphicsub2text_class,
+ FILTER_INPUTS(inputs),
+ FILTER_OUTPUTS(outputs),
+ FILTER_QUERY_FUNC(query_formats),
+};
--
2.30.2.windows.1
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