FFmpeg
webvttenc.c
Go to the documentation of this file.
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 {
34  AVBPrint buffer;
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;
163 
164  av_bprint_clear(&s->buffer);
165 
166  for (i=0; i<sub->num_rects; i++) {
167  const char *ass = sub->rects[i]->ass;
168 
169  if (sub->rects[i]->type != SUBTITLE_ASS) {
170  av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
171  return AVERROR(EINVAL);
172  }
173 
174 #if FF_API_ASS_TIMING
175  if (!strncmp(ass, "Dialogue: ", 10)) {
176  int num;
177  dialog = ff_ass_split_dialog(s->ass_ctx, ass, 0, &num);
178  // TODO reindent
179  for (; dialog && num--; dialog++) {
180  webvtt_style_apply(s, dialog->style);
182  }
183  } else {
184 #endif
185  dialog = ff_ass_split_dialog2(s->ass_ctx, ass);
186  if (!dialog)
187  return AVERROR(ENOMEM);
188  webvtt_style_apply(s, dialog->style);
190  ff_ass_free_dialog(&dialog);
191 #if FF_API_ASS_TIMING
192  }
193 #endif
194  }
195 
196  if (!av_bprint_is_complete(&s->buffer))
197  return AVERROR(ENOMEM);
198  if (!s->buffer.len)
199  return 0;
200 
201  if (s->buffer.len > bufsize) {
202  av_log(avctx, AV_LOG_ERROR, "Buffer too small for ASS event.\n");
204  }
205  memcpy(buf, s->buffer.str, s->buffer.len);
206 
207  return s->buffer.len;
208 }
209 
211 {
212  WebVTTContext *s = avctx->priv_data;
213  ff_ass_split_free(s->ass_ctx);
214  av_bprint_finalize(&s->buffer, NULL);
215  return 0;
216 }
217 
219 {
220  WebVTTContext *s = avctx->priv_data;
221  s->avctx = avctx;
222  s->ass_ctx = ff_ass_split(avctx->subtitle_header);
224  return s->ass_ctx ? 0 : AVERROR_INVALIDDATA;
225 }
226 
228  .name = "webvtt",
229  .long_name = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
230  .type = AVMEDIA_TYPE_SUBTITLE,
231  .id = AV_CODEC_ID_WEBVTT,
232  .priv_data_size = sizeof(WebVTTContext),
234  .encode_sub = webvtt_encode_frame,
235  .close = webvtt_encode_close,
236 };
AVSubtitle
Definition: avcodec.h:2722
AVCodec
AVCodec.
Definition: codec.h:197
AVMEDIA_TYPE_SUBTITLE
@ AVMEDIA_TYPE_SUBTITLE
Definition: avutil.h:204
AV_BPRINT_SIZE_UNLIMITED
#define AV_BPRINT_SIZE_UNLIMITED
webvtt_print
static void webvtt_print(WebVTTContext *s, const char *str,...)
Definition: webvttenc.c:44
init
static av_cold int init(AVCodecContext *avctx)
Definition: avrndec.c:31
ASSCodesCallbacks
Set of callback functions corresponding to each override codes that can be encountered in a "Dialogue...
Definition: ass_split.h:154
AVERROR
Filter the word “frame” indicates either a video frame or a group of audio as stored in an AVFrame structure Format for each input and each output the list of supported formats For video that means pixel format For audio that means channel sample they are references to shared objects When the negotiation mechanism computes the intersection of the formats supported at each end of a all references to both lists are replaced with a reference to the intersection And when a single format is eventually chosen for a link amongst the remaining all references to the list are updated That means that if a filter requires that its input and output have the same format amongst a supported all it has to do is use a reference to the same list of formats query_formats can leave some formats unset and return AVERROR(EAGAIN) to cause the negotiation mechanism toagain later. That can be used by filters with complex requirements to use the format negotiated on one link to set the formats supported on another. Frame references ownership and permissions
ff_ass_split_dialog
ASSDialog * ff_ass_split_dialog(ASSSplitContext *ctx, const char *buf, int cache, int *number)
Split one or several ASS "Dialogue" lines from a string buffer and store them in an already initializ...
Definition: ass_split.c:413
av_bprint_finalize
int av_bprint_finalize(AVBPrint *buf, char **ret_str)
Finalize a print buffer.
Definition: bprint.c:235
av_bprint_init
void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max)
Definition: bprint.c:69
sub
static float sub(float src0, float src1)
Definition: dnn_backend_native_layer_mathbinary.c:32
webvtt_stack_pop
static char webvtt_stack_pop(WebVTTContext *s)
Definition: webvttenc.c:60
WebVTTContext
Definition: webvttenc.c:31
AVCodecContext::subtitle_header
uint8_t * subtitle_header
Header containing style information for text subtitles.
Definition: avcodec.h:2016
av_bprint_append_data
void av_bprint_append_data(AVBPrint *buf, const char *data, unsigned size)
Append data to a print buffer.
Definition: bprint.c:158
ASSDialog::style
char * style
name of the ASSStyle to use with this dialog
Definition: ass_split.h:76
SUBTITLE_ASS
@ SUBTITLE_ASS
Formatted text, the ass field must be set by the decoder and is authoritative.
Definition: avcodec.h:2682
webvtt_encode_init
static av_cold int webvtt_encode_init(AVCodecContext *avctx)
Definition: webvttenc.c:218
ass_split.h
WEBVTT_STACK_SIZE
#define WEBVTT_STACK_SIZE
Definition: webvttenc.c:30
AVERROR_BUFFER_TOO_SMALL
#define AVERROR_BUFFER_TOO_SMALL
Buffer too small.
Definition: error.h:51
ass.h
ff_ass_free_dialog
void ff_ass_free_dialog(ASSDialog **dialogp)
Free a dialogue obtained from ff_ass_split_dialog2().
Definition: ass_split.c:432
AV_LOG_ERROR
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:194
av_cold
#define av_cold
Definition: attributes.h:90
s
#define s(width, name)
Definition: cbs_vp9.c:257
ff_ass_split_dialog2
ASSDialog * ff_ass_split_dialog2(ASSSplitContext *ctx, const char *buf)
Split one ASS Dialogue line from a string buffer.
Definition: ass_split.c:444
WebVTTContext::stack_ptr
int stack_ptr
Definition: webvttenc.c:38
AV_CODEC_ID_WEBVTT
@ AV_CODEC_ID_WEBVTT
Definition: codec_id.h:542
av_vbprintf
void av_vbprintf(AVBPrint *buf, const char *fmt, va_list vl_arg)
Append a formatted string to a print buffer.
Definition: bprint.c:117
NULL
#define NULL
Definition: coverity.c:32
webvtt_stack_find
static int webvtt_stack_find(WebVTTContext *s, const char c)
Definition: webvttenc.c:67
webvtt_encode_frame
static int webvtt_encode_frame(AVCodecContext *avctx, unsigned char *buf, int bufsize, const AVSubtitle *sub)
Definition: webvttenc.c:157
ASSSplitContext
This struct can be casted to ASS to access to the split data.
Definition: ass_split.c:197
ff_ass_split
ASSSplitContext * ff_ass_split(const char *buf)
Split a full ASS file or a ASS header from a string buffer and store the split structure in a newly a...
Definition: ass_split.c:374
webvtt_text_cb
static void webvtt_text_cb(void *priv, const char *text, int len)
Definition: webvttenc.c:112
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
ASSStyle
fields extracted from the [V4(+) Styles] section
Definition: ass_split.h:39
av_bprint_is_complete
static int av_bprint_is_complete(const AVBPrint *buf)
Test if the print buffer is complete (not truncated).
Definition: bprint.h:185
ASSStyle::underline
int underline
whether text is underlined (1) or not (0)
Definition: ass_split.h:49
webvtt_callbacks
static const ASSCodesCallbacks webvtt_callbacks
Definition: webvttenc.c:144
ff_ass_split_free
void ff_ass_split_free(ASSSplitContext *ctx)
Free all the memory allocated for an ASSSplitContext.
Definition: ass_split.c:481
ASS_DEFAULT_BOLD
#define ASS_DEFAULT_BOLD
Definition: ass.h:39
NULL_IF_CONFIG_SMALL
#define NULL_IF_CONFIG_SMALL(x)
Return NULL if CONFIG_SMALL is true, otherwise the argument without modification.
Definition: internal.h:117
ASSDialog::text
char * text
actual text which will be displayed as a subtitle, can include style override control codes (see ff_a...
Definition: ass_split.h:82
webvtt_stack_push
static int webvtt_stack_push(WebVTTContext *s, const char c)
Definition: webvttenc.c:52
WebVTTContext::count
int count
Definition: webvttenc.c:36
ASSStyle::italic
int italic
whether text is italic (1) or not (0)
Definition: ass_split.h:48
webvtt_cancel_overrides_cb
static void webvtt_cancel_overrides_cb(void *priv, const char *style)
Definition: webvttenc.c:133
ASS_DEFAULT_UNDERLINE
#define ASS_DEFAULT_UNDERLINE
Definition: ass.h:41
webvtt_end_cb
static void webvtt_end_cb(void *priv)
Definition: webvttenc.c:139
ff_ass_style_get
ASSStyle * ff_ass_style_get(ASSSplitContext *ctx, const char *style)
Find an ASSStyle structure by its name.
Definition: ass_split.c:589
ff_webvtt_encoder
AVCodec ff_webvtt_encoder
Definition: webvttenc.c:227
bprint.h
i
int i
Definition: input.c:407
webvtt_style_cb
static void webvtt_style_cb(void *priv, char style, int close)
Definition: webvttenc.c:123
WebVTTContext::avctx
AVCodecContext * avctx
Definition: webvttenc.c:32
AVCodec::name
const char * name
Name of the codec implementation.
Definition: codec.h:204
ASS_DEFAULT_ITALIC
#define ASS_DEFAULT_ITALIC
Definition: ass.h:40
len
int len
Definition: vorbis_enc_data.h:452
avcodec.h
tag
uint32_t tag
Definition: movenc.c:1611
WebVTTContext::ass_ctx
ASSSplitContext * ass_ctx
Definition: webvttenc.c:33
webvtt_new_line_cb
static void webvtt_new_line_cb(void *priv, int forced)
Definition: webvttenc.c:118
AVCodecContext
main external API structure.
Definition: avcodec.h:536
av_bprint_clear
void av_bprint_clear(AVBPrint *buf)
Reset the string to "" but keep internal allocated data.
Definition: bprint.c:227
WebVTTContext::buffer
AVBPrint buffer
Definition: webvttenc.c:34
webvtt_stack_push_pop
static void webvtt_stack_push_pop(WebVTTContext *s, const char c, int close)
Definition: webvttenc.c:81
ASSDialog
fields extracted from the [Events] section
Definition: ass_split.h:71
webvtt_style_apply
static void webvtt_style_apply(WebVTTContext *s, const char *style)
Definition: webvttenc.c:93
webvtt_encode_close
static int webvtt_encode_close(AVCodecContext *avctx)
Definition: webvttenc.c:210
AVCodecContext::priv_data
void * priv_data
Definition: avcodec.h:563
convert_header.str
string str
Definition: convert_header.py:20
av_log
#define av_log(a,...)
Definition: tableprint_vlc.h:28
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
ff_ass_split_override_codes
int ff_ass_split_override_codes(const ASSCodesCallbacks *callbacks, void *priv, const char *buf)
Split override codes out of a ASS "Dialogue" Text field.
Definition: ass_split.c:494
avstring.h
webvtt_close_tag
static void webvtt_close_tag(WebVTTContext *s, char tag)
Definition: webvttenc.c:76
ASSStyle::bold
int bold
whether text is bold (1) or not (0)
Definition: ass_split.h:47
WebVTTContext::timestamp_end
unsigned timestamp_end
Definition: webvttenc.c:35
ASSCodesCallbacks::text
void(* text)(void *priv, const char *text, int len)
Definition: ass_split.h:159