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;
93 if (sub->rects[i]->type != SUBTITLE_ASS) {
94 av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
95 return AVERROR(EINVAL);
98 dialog = ff_ass_split_dialog2(s->ass_ctx, ass);
100 return AVERROR(ENOMEM);
103 av_bprintf(&s->buffer, "<span region=\"");
104 av_bprint_escape(&s->buffer, dialog->style, NULL,
106 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
107 av_bprintf(&s->buffer, "\">");
110 ret = ff_ass_split_override_codes(&ttml_callbacks, s, dialog->text);
112 int log_level = (ret != AVERROR_INVALIDDATA ||
113 avctx->err_recognition & AV_EF_EXPLODE) ?
114 AV_LOG_ERROR : AV_LOG_WARNING;
115 av_log(avctx, log_level,
116 "Splitting received ASS dialog text %s failed: %s\n",
120 if (log_level == AV_LOG_ERROR) {
121 ff_ass_free_dialog(&dialog);
127 av_bprintf(&s->buffer, "</span>");
129 ff_ass_free_dialog(&dialog);
132 if (!av_bprint_is_complete(&s->buffer))
133 return AVERROR(ENOMEM);
137 // force null-termination, so in case our destination buffer is
138 // too small, the return value is larger than bufsize minus null.
139 if (av_strlcpy(buf, s->buffer.str, bufsize) > bufsize - 1) {
140 av_log(avctx, AV_LOG_ERROR, "Buffer too small for TTML event.\n");
141 return AVERROR_BUFFER_TOO_SMALL;
144 return s->buffer.len;
147 static av_cold int ttml_encode_close(AVCodecContext *avctx)
149 TTMLContext *s = avctx->priv_data;
151 ff_ass_split_free(s->ass_ctx);
153 av_bprint_finalize(&s->buffer, NULL);
158 static const char *ttml_get_display_alignment(int alignment)
178 static const char *ttml_get_text_alignment(int alignment)
198 static void ttml_get_origin(ASSScriptInfo script_info, ASSStyle style,
199 int *origin_left, int *origin_top)
201 *origin_left = av_rescale(style.margin_l, 100, script_info.play_res_x);
203 av_rescale((style.alignment >= 7) ? style.margin_v : 0,
204 100, script_info.play_res_y);
207 static void ttml_get_extent(ASSScriptInfo script_info, ASSStyle style,
208 int *width, int *height)
210 *width = av_rescale(script_info.play_res_x - style.margin_r,
211 100, script_info.play_res_x);
212 *height = av_rescale((style.alignment <= 3) ?
213 script_info.play_res_y - style.margin_v :
214 script_info.play_res_y,
215 100, script_info.play_res_y);
218 static int ttml_write_region(AVCodecContext *avctx, AVBPrint *buf,
219 ASSScriptInfo script_info, ASSStyle style)
221 const char *display_alignment = NULL;
222 const char *text_alignment = NULL;
229 av_log(avctx, AV_LOG_ERROR, "Subtitle style name not set!\n");
230 return AVERROR_INVALIDDATA;
233 if (style.font_size < 0) {
234 av_log(avctx, AV_LOG_ERROR, "Invalid font size for TTML: %d!\n",
236 return AVERROR_INVALIDDATA;
239 if (style.margin_l < 0 || style.margin_r < 0 || style.margin_v < 0) {
240 av_log(avctx, AV_LOG_ERROR,
241 "One or more negative margin values in subtitle style: "
242 "left: %d, right: %d, vertical: %d!\n",
243 style.margin_l, style.margin_r, style.margin_v);
244 return AVERROR_INVALIDDATA;
247 display_alignment = ttml_get_display_alignment(style.alignment);
248 text_alignment = ttml_get_text_alignment(style.alignment);
249 if (!display_alignment || !text_alignment) {
250 av_log(avctx, AV_LOG_ERROR,
251 "Failed to convert ASS style alignment %d of style %s to "
252 "TTML display and text alignment!\n",
255 return AVERROR_INVALIDDATA;
258 ttml_get_origin(script_info, style, &origin_left, &origin_top);
259 ttml_get_extent(script_info, style, &width, &height);
261 av_bprintf(buf, " <region xml:id=\"");
262 av_bprint_escape(buf, style.name, NULL, AV_ESCAPE_MODE_XML,
263 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
264 av_bprintf(buf, "\"\n");
266 av_bprintf(buf, " tts:origin=\"%d%% %d%%\"\n",
267 origin_left, origin_top);
268 av_bprintf(buf, " tts:extent=\"%d%% %d%%\"\n",
271 av_bprintf(buf, " tts:displayAlign=\"");
272 av_bprint_escape(buf, display_alignment, NULL, AV_ESCAPE_MODE_XML,
273 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
274 av_bprintf(buf, "\"\n");
276 av_bprintf(buf, " tts:textAlign=\"");
277 av_bprint_escape(buf, text_alignment, NULL, AV_ESCAPE_MODE_XML,
278 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
279 av_bprintf(buf, "\"\n");
281 // if we set cell resolution to our script reference resolution,
282 // then a single line is a single "point" on our canvas. Thus, by setting
283 // our font size to font size in cells, we should gain a similar enough
284 // scale without resorting to explicit pixel based font sizing, which is
285 // frowned upon in the TTML community.
286 av_bprintf(buf, " tts:fontSize=\"%dc\"\n",
289 if (style.font_name) {
290 av_bprintf(buf, " tts:fontFamily=\"");
291 av_bprint_escape(buf, style.font_name, NULL, AV_ESCAPE_MODE_XML,
292 AV_ESCAPE_FLAG_XML_DOUBLE_QUOTES);
293 av_bprintf(buf, "\"\n");
296 av_bprintf(buf, " tts:overflow=\"visible\" />\n");
301 static int ttml_write_header_content(AVCodecContext *avctx)
303 TTMLContext *s = avctx->priv_data;
304 ASS *ass = (ASS *)s->ass_ctx;
305 ASSScriptInfo script_info = ass->script_info;
306 const size_t base_extradata_size = TTMLENC_EXTRADATA_SIGNATURE_SIZE + 1 +
307 AV_INPUT_BUFFER_PADDING_SIZE;
308 size_t additional_extradata_size = 0;
310 if (script_info.play_res_x <= 0 || script_info.play_res_y <= 0) {
311 av_log(avctx, AV_LOG_ERROR,
312 "Invalid subtitle reference resolution %dx%d!\n",
313 script_info.play_res_x, script_info.play_res_y);
314 return AVERROR_INVALIDDATA;
317 // write the first string in extradata, attributes in the base "tt" element.
318 av_bprintf(&s->buffer, ttml_default_namespacing);
319 // the cell resolution is in character cells, so not exactly 1:1 against
320 // a pixel based resolution, but as the tts:extent in the root
321 // "tt" element is frowned upon (and disallowed in the EBU-TT profile),
322 // we mimic the reference resolution by setting it as the cell resolution.
323 av_bprintf(&s->buffer, " ttp:cellResolution=\"%d %d\"\n",
324 script_info.play_res_x, script_info.play_res_y);
325 av_bprint_chars(&s->buffer, '\0', 1);
327 // write the second string in extradata, head element containing the styles
328 av_bprintf(&s->buffer, " <head>\n");
329 av_bprintf(&s->buffer, " <layout>\n");
331 for (int i = 0; i < ass->styles_count; i++) {
332 int ret = ttml_write_region(avctx, &s->buffer, script_info,
338 av_bprintf(&s->buffer, " </layout>\n");
339 av_bprintf(&s->buffer, " </head>\n");
340 av_bprint_chars(&s->buffer, '\0', 1);
342 if (!av_bprint_is_complete(&s->buffer)) {
343 return AVERROR(ENOMEM);
346 additional_extradata_size = s->buffer.len;
348 if (!(avctx->extradata =
349 av_mallocz(base_extradata_size + additional_extradata_size))) {
350 return AVERROR(ENOMEM);
353 avctx->extradata_size =
354 TTMLENC_EXTRADATA_SIGNATURE_SIZE + additional_extradata_size;
355 memcpy(avctx->extradata, TTMLENC_EXTRADATA_SIGNATURE,
356 TTMLENC_EXTRADATA_SIGNATURE_SIZE);
358 if (additional_extradata_size)
359 memcpy(avctx->extradata + TTMLENC_EXTRADATA_SIGNATURE_SIZE,
360 s->buffer.str, additional_extradata_size);
362 av_bprint_clear(&s->buffer);
367 static av_cold int ttml_encode_init(AVCodecContext *avctx)
369 TTMLContext *s = avctx->priv_data;
370 int ret = AVERROR_BUG;
373 av_bprint_init(&s->buffer, 0, AV_BPRINT_SIZE_UNLIMITED);
375 if (!(s->ass_ctx = ff_ass_split(avctx->subtitle_header))) {
376 return AVERROR_INVALIDDATA;
379 if ((ret = ttml_write_header_content(avctx)) < 0) {
386 const AVCodec ff_ttml_encoder = {
388 .long_name = NULL_IF_CONFIG_SMALL("TTML subtitle"),
389 .type = AVMEDIA_TYPE_SUBTITLE,
390 .id = AV_CODEC_ID_TTML,
391 .priv_data_size = sizeof(TTMLContext),
392 .init = ttml_encode_init,
393 .encode_sub = ttml_encode_frame,
394 .close = ttml_encode_close,
395 .capabilities = FF_CODEC_CAP_INIT_CLEANUP,