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webvttenc.c
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1 /*
2  * WebVTT subtitle encoder
3  * Copyright (c) 2010 Aurelien Jacobs <aurel@gnuage.org>
4  * Copyright (c) 2014 Aman Gupta <ffmpeg@tmm1.net>
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include <stdarg.h>
24 #include "avcodec.h"
25 #include "libavutil/avstring.h"
26 #include "libavutil/bprint.h"
27 #include "ass_split.h"
28 #include "ass.h"
29 
30 #define WEBVTT_STACK_SIZE 64
31 typedef struct {
35  unsigned timestamp_end;
36  int count;
37  char stack[WEBVTT_STACK_SIZE];
38  int stack_ptr;
40 
41 #ifdef __GNUC__
42 __attribute__ ((__format__ (__printf__, 2, 3)))
43 #endif
44 static void webvtt_print(WebVTTContext *s, const char *str, ...)
45 {
46  va_list vargs;
47  va_start(vargs, str);
48  av_vbprintf(&s->buffer, str, vargs);
49  va_end(vargs);
50 }
51 
52 static int webvtt_stack_push(WebVTTContext *s, const char c)
53 {
54  if (s->stack_ptr >= WEBVTT_STACK_SIZE)
55  return -1;
56  s->stack[s->stack_ptr++] = c;
57  return 0;
58 }
59 
61 {
62  if (s->stack_ptr <= 0)
63  return 0;
64  return s->stack[--s->stack_ptr];
65 }
66 
67 static int webvtt_stack_find(WebVTTContext *s, const char c)
68 {
69  int i;
70  for (i = s->stack_ptr-1; i >= 0; i--)
71  if (s->stack[i] == c)
72  break;
73  return i;
74 }
75 
76 static void webvtt_close_tag(WebVTTContext *s, char tag)
77 {
78  webvtt_print(s, "</%c>", tag);
79 }
80 
81 static void webvtt_stack_push_pop(WebVTTContext *s, const char c, int close)
82 {
83  if (close) {
84  int i = c ? webvtt_stack_find(s, c) : 0;
85  if (i < 0)
86  return;
87  while (s->stack_ptr != i)
89  } else if (webvtt_stack_push(s, c) < 0)
90  av_log(s->avctx, AV_LOG_ERROR, "tag stack overflow\n");
91 }
92 
93 static void webvtt_style_apply(WebVTTContext *s, const char *style)
94 {
95  ASSStyle *st = ff_ass_style_get(s->ass_ctx, style);
96  if (st) {
97  if (st->bold != ASS_DEFAULT_BOLD) {
98  webvtt_print(s, "<b>");
99  webvtt_stack_push(s, 'b');
100  }
101  if (st->italic != ASS_DEFAULT_ITALIC) {
102  webvtt_print(s, "<i>");
103  webvtt_stack_push(s, 'i');
104  }
105  if (st->underline != ASS_DEFAULT_UNDERLINE) {
106  webvtt_print(s, "<u>");
107  webvtt_stack_push(s, 'u');
108  }
109  }
110 }
111 
112 static void webvtt_text_cb(void *priv, const char *text, int len)
113 {
114  WebVTTContext *s = priv;
115  av_bprint_append_data(&s->buffer, text, len);
116 }
117 
118 static void webvtt_new_line_cb(void *priv, int forced)
119 {
120  webvtt_print(priv, "\n");
121 }
122 
123 static void webvtt_style_cb(void *priv, char style, int close)
124 {
125  if (style == 's') // strikethrough unsupported
126  return;
127 
128  webvtt_stack_push_pop(priv, style, close);
129  if (!close)
130  webvtt_print(priv, "<%c>", style);
131 }
132 
133 static void webvtt_cancel_overrides_cb(void *priv, const char *style)
134 {
135  webvtt_stack_push_pop(priv, 0, 1);
136  webvtt_style_apply(priv, style);
137 }
138 
139 static void webvtt_end_cb(void *priv)
140 {
141  webvtt_stack_push_pop(priv, 0, 1);
142 }
143 
145  .text = webvtt_text_cb,
146  .new_line = webvtt_new_line_cb,
147  .style = webvtt_style_cb,
148  .color = NULL,
149  .font_name = NULL,
150  .font_size = NULL,
151  .alignment = NULL,
152  .cancel_overrides = webvtt_cancel_overrides_cb,
153  .move = NULL,
154  .end = webvtt_end_cb,
155 };
156 
158  unsigned char *buf, int bufsize, const AVSubtitle *sub)
159 {
160  WebVTTContext *s = avctx->priv_data;
161  ASSDialog *dialog;
162  int i, num;
163 
164  av_bprint_clear(&s->buffer);
165 
166  for (i=0; i<sub->num_rects; i++) {
167  if (sub->rects[i]->type != SUBTITLE_ASS) {
168  av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
169  return AVERROR(ENOSYS);
170  }
171 
172  dialog = ff_ass_split_dialog(s->ass_ctx, sub->rects[i]->ass, 0, &num);
173  for (; dialog && num--; dialog++) {
174  webvtt_style_apply(s, dialog->style);
175  ff_ass_split_override_codes(&webvtt_callbacks, s, dialog->text);
176  }
177  }
178 
179  if (!av_bprint_is_complete(&s->buffer))
180  return AVERROR(ENOMEM);
181  if (!s->buffer.len)
182  return 0;
183 
184  if (s->buffer.len > bufsize) {
185  av_log(avctx, AV_LOG_ERROR, "Buffer too small for ASS event.\n");
186  return -1;
187  }
188  memcpy(buf, s->buffer.str, s->buffer.len);
189 
190  return s->buffer.len;
191 }
192 
194 {
195  WebVTTContext *s = avctx->priv_data;
197  av_bprint_finalize(&s->buffer, NULL);
198  return 0;
199 }
200 
202 {
203  WebVTTContext *s = avctx->priv_data;
204  s->avctx = avctx;
205  s->ass_ctx = ff_ass_split(avctx->subtitle_header);
207  return s->ass_ctx ? 0 : AVERROR_INVALIDDATA;
208 }
209 
211  .name = "webvtt",
212  .long_name = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
213  .type = AVMEDIA_TYPE_SUBTITLE,
214  .id = AV_CODEC_ID_WEBVTT,
215  .priv_data_size = sizeof(WebVTTContext),
217  .encode_sub = webvtt_encode_frame,
219 };