2 * TTML subtitle encoder
3 * Copyright (c) 2020 24i
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 * TTML subtitle encoder
25 * @see https://www.w3.org/TR/ttml1/
26 * @see https://www.w3.org/TR/ttml2/
27 * @see https://www.w3.org/TR/ttml-imsc/rec
32 #include "libavutil/avstring.h"
33 #include "libavutil/bprint.h"
34 #include "libavutil/internal.h"
35 #include "ass_split.h"
40 AVCodecContext *avctx;
41 ASSSplitContext *ass_ctx;
45 static void ttml_text_cb(void *priv, const char *text, int len)
47 TTMLContext *s = priv;
48 AVBPrint cur_line = { 0 };
49 AVBPrint *buffer = &s->buffer;
51 av_bprint_init(&cur_line, len, AV_BPRINT_SIZE_UNLIMITED);
53 av_bprint_append_data(&cur_line, text, len);
54 if (!av_bprint_is_complete(&cur_line)) {
55 av_log(s->avctx, AV_LOG_ERROR,
56 "Failed to move the current subtitle dialog to AVBPrint!\n");
57 av_bprint_finalize(&cur_line, NULL);
62 av_bprint_escape(buffer, cur_line.str, NULL, AV_ESCAPE_MODE_XML,
65 av_bprint_finalize(&cur_line, NULL);
68 static void ttml_new_line_cb(void *priv, int forced)
70 TTMLContext *s = priv;
72 av_bprintf(&s->buffer, "<br/>");
75 static const ASSCodesCallbacks ttml_callbacks = {
77 .new_line = ttml_new_line_cb,
80 static int ttml_encode_frame(AVCodecContext *avctx, uint8_t *buf,
81 int bufsize, const AVSubtitle *sub)
83 TTMLContext *s = avctx->priv_data;
87 av_bprint_clear(&s->buffer);
89 for (i=0; i<sub->num_rects; i++) {
90 const char *ass = sub->rects[i]->ass;
92 if (sub->rects[i]->type != SUBTITLE_ASS) {
93 av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
94 return AVERROR(EINVAL);
97 dialog = ff_ass_split_dialog2(s->ass_ctx, ass);
99 return AVERROR(ENOMEM);
102 av_bprintf(&s->buffer, "<span region=\"");
103 av_bprint_escape(&s->buffer, dialog->style, NULL,
105 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
106 av_bprintf(&s->buffer, "\">");
110 int ret = ff_ass_split_override_codes(&ttml_callbacks, s,
112 int log_level = (ret != AVERROR_INVALIDDATA ||
113 avctx->err_recognition & AV_EF_EXPLODE) ?
114 AV_LOG_ERROR : AV_LOG_WARNING;
117 av_log(avctx, log_level,
118 "Splitting received ASS dialog text %s failed: %s\n",
122 if (log_level == AV_LOG_ERROR) {
123 ff_ass_free_dialog(&dialog);
129 av_bprintf(&s->buffer, "</span>");
131 ff_ass_free_dialog(&dialog);
135 if (!av_bprint_is_complete(&s->buffer))
136 return AVERROR(ENOMEM);
140 // force null-termination, so in case our destination buffer is
141 // too small, the return value is larger than bufsize minus null.
142 if (av_strlcpy(buf, s->buffer.str, bufsize) > bufsize - 1) {
143 av_log(avctx, AV_LOG_ERROR, "Buffer too small for TTML event.\n");
144 return AVERROR_BUFFER_TOO_SMALL;
147 return s->buffer.len;
150 static av_cold int ttml_encode_close(AVCodecContext *avctx)
152 TTMLContext *s = avctx->priv_data;
154 ff_ass_split_free(s->ass_ctx);
156 av_bprint_finalize(&s->buffer, NULL);
161 static const char *ttml_get_display_alignment(int alignment)
181 static const char *ttml_get_text_alignment(int alignment)
201 static void ttml_get_origin(ASSScriptInfo script_info, ASSStyle style,
202 int *origin_left, int *origin_top)
204 *origin_left = av_rescale(style.margin_l, 100, script_info.play_res_x);
206 av_rescale((style.alignment >= 7) ? style.margin_v : 0,
207 100, script_info.play_res_y);
210 static void ttml_get_extent(ASSScriptInfo script_info, ASSStyle style,
211 int *width, int *height)
213 *width = av_rescale(script_info.play_res_x - style.margin_r,
214 100, script_info.play_res_x);
215 *height = av_rescale((style.alignment <= 3) ?
216 script_info.play_res_y - style.margin_v :
217 script_info.play_res_y,
218 100, script_info.play_res_y);
221 static int ttml_write_region(AVCodecContext *avctx, AVBPrint *buf,
222 ASSScriptInfo script_info, ASSStyle style)
224 const char *display_alignment = NULL;
225 const char *text_alignment = NULL;
232 av_log(avctx, AV_LOG_ERROR, "Subtitle style name not set!\n");
233 return AVERROR_INVALIDDATA;
236 if (style.font_size < 0) {
237 av_log(avctx, AV_LOG_ERROR, "Invalid font size for TTML: %d!\n",
239 return AVERROR_INVALIDDATA;
242 if (style.margin_l < 0 || style.margin_r < 0 || style.margin_v < 0) {
243 av_log(avctx, AV_LOG_ERROR,
244 "One or more negative margin values in subtitle style: "
245 "left: %d, right: %d, vertical: %d!\n",
246 style.margin_l, style.margin_r, style.margin_v);
247 return AVERROR_INVALIDDATA;
250 display_alignment = ttml_get_display_alignment(style.alignment);
251 text_alignment = ttml_get_text_alignment(style.alignment);
252 if (!display_alignment || !text_alignment) {
253 av_log(avctx, AV_LOG_ERROR,
254 "Failed to convert ASS style alignment %d of style %s to "
255 "TTML display and text alignment!\n",
258 return AVERROR_INVALIDDATA;
261 ttml_get_origin(script_info, style, &origin_left, &origin_top);
262 ttml_get_extent(script_info, style, &width, &height);
264 av_bprintf(buf, " <region xml:id=\"");
265 av_bprint_escape(buf, style.name, NULL, AV_ESCAPE_MODE_XML,
266 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
267 av_bprintf(buf, "\"\n");
269 av_bprintf(buf, " tts:origin=\"%d%% %d%%\"\n",
270 origin_left, origin_top);
271 av_bprintf(buf, " tts:extent=\"%d%% %d%%\"\n",
274 av_bprintf(buf, " tts:displayAlign=\"");
275 av_bprint_escape(buf, display_alignment, NULL, AV_ESCAPE_MODE_XML,
276 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
277 av_bprintf(buf, "\"\n");
279 av_bprintf(buf, " tts:textAlign=\"");
280 av_bprint_escape(buf, text_alignment, NULL, AV_ESCAPE_MODE_XML,
281 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
282 av_bprintf(buf, "\"\n");
284 // if we set cell resolution to our script reference resolution,
285 // then a single line is a single "point" on our canvas. Thus, by setting
286 // our font size to font size in cells, we should gain a similar enough
287 // scale without resorting to explicit pixel based font sizing, which is
288 // frowned upon in the TTML community.
289 av_bprintf(buf, " tts:fontSize=\"%dc\"\n",
292 if (style.font_name) {
293 av_bprintf(buf, " tts:fontFamily=\"");
294 av_bprint_escape(buf, style.font_name, NULL, AV_ESCAPE_MODE_XML,
295 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
296 av_bprintf(buf, "\"\n");
299 av_bprintf(buf, " tts:overflow=\"visible\" />\n");
304 static int ttml_write_header_content(AVCodecContext *avctx)
306 TTMLContext *s = avctx->priv_data;
307 ASS *ass = (ASS *)s->ass_ctx;
308 ASSScriptInfo script_info = ass->script_info;
309 const size_t base_extradata_size = TTMLENC_EXTRADATA_SIGNATURE_SIZE + 1 +
310 AV_INPUT_BUFFER_PADDING_SIZE;
311 size_t additional_extradata_size = 0;
313 if (script_info.play_res_x <= 0 || script_info.play_res_y <= 0) {
314 av_log(avctx, AV_LOG_ERROR,
315 "Invalid subtitle reference resolution %dx%d!\n",
316 script_info.play_res_x, script_info.play_res_y);
317 return AVERROR_INVALIDDATA;
320 // write the first string in extradata, attributes in the base "tt" element.
321 av_bprintf(&s->buffer, ttml_default_namespacing);
322 // the cell resolution is in character cells, so not exactly 1:1 against
323 // a pixel based resolution, but as the tts:extent in the root
324 // "tt" element is frowned upon (and disallowed in the EBU-TT profile),
325 // we mimic the reference resolution by setting it as the cell resolution.
326 av_bprintf(&s->buffer, " ttp:cellResolution=\"%d %d\"\n",
327 script_info.play_res_x, script_info.play_res_y);
328 av_bprint_chars(&s->buffer, '\0', 1);
330 // write the second string in extradata, head element containing the styles
331 av_bprintf(&s->buffer, " <head>\n");
332 av_bprintf(&s->buffer, " <layout>\n");
334 for (int i = 0; i < ass->styles_count; i++) {
335 int ret = ttml_write_region(avctx, &s->buffer, script_info,
341 av_bprintf(&s->buffer, " </layout>\n");
342 av_bprintf(&s->buffer, " </head>\n");
343 av_bprint_chars(&s->buffer, '\0', 1);
345 if (!av_bprint_is_complete(&s->buffer)) {
346 return AVERROR(ENOMEM);
349 additional_extradata_size = s->buffer.len;
351 if (!(avctx->extradata =
352 av_mallocz(base_extradata_size + additional_extradata_size))) {
353 return AVERROR(ENOMEM);
356 avctx->extradata_size =
357 TTMLENC_EXTRADATA_SIGNATURE_SIZE + additional_extradata_size;
358 memcpy(avctx->extradata, TTMLENC_EXTRADATA_SIGNATURE,
359 TTMLENC_EXTRADATA_SIGNATURE_SIZE);
361 if (additional_extradata_size)
362 memcpy(avctx->extradata + TTMLENC_EXTRADATA_SIGNATURE_SIZE,
363 s->buffer.str, additional_extradata_size);
365 av_bprint_clear(&s->buffer);
370 static av_cold int ttml_encode_init(AVCodecContext *avctx)
372 TTMLContext *s = avctx->priv_data;
373 int ret = AVERROR_BUG;
376 av_bprint_init(&s->buffer, 0, AV_BPRINT_SIZE_UNLIMITED);
378 if (!(s->ass_ctx = ff_ass_split(avctx->subtitle_header))) {
379 return AVERROR_INVALIDDATA;
382 if ((ret = ttml_write_header_content(avctx)) < 0) {
389 AVCodec ff_ttml_encoder = {
391 .long_name = NULL_IF_CONFIG_SMALL("TTML subtitle"),
392 .type = AVMEDIA_TYPE_SUBTITLE,
393 .id = AV_CODEC_ID_TTML,
394 .priv_data_size = sizeof(TTMLContext),
395 .init = ttml_encode_init,
396 .encode_sub = ttml_encode_frame,
397 .close = ttml_encode_close,
398 .capabilities = FF_CODEC_CAP_INIT_CLEANUP,