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movtextdec.c
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1 /*
2  * 3GPP TS 26.245 Timed Text decoder
3  * Copyright (c) 2012 Philip Langdale <philipl@overt.org>
4  *
5  * This file is part of FFmpeg.
6  *
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.
11  *
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.
16  *
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
20  */
21 
22 #include "avcodec.h"
23 #include "ass.h"
24 #include "libavutil/avstring.h"
25 #include "libavutil/common.h"
26 #include "libavutil/bprint.h"
27 #include "libavutil/intreadwrite.h"
28 
29 static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end)
30 {
31  while (text < text_end) {
32  switch (*text) {
33  case '\r':
34  break;
35  case '\n':
36  av_bprintf(buf, "\\N");
37  break;
38  default:
39  av_bprint_chars(buf, *text, 1);
40  break;
41  }
42  text++;
43  }
44 
45  return 0;
46 }
47 
48 static int mov_text_init(AVCodecContext *avctx) {
49  /*
50  * TODO: Handle the default text style.
51  * NB: Most players ignore styles completely, with the result that
52  * it's very common to find files where the default style is broken
53  * and respecting it results in a worse experience than ignoring it.
54  */
55  return ff_ass_subtitle_header_default(avctx);
56 }
57 
59  void *data, int *got_sub_ptr, AVPacket *avpkt)
60 {
61  AVSubtitle *sub = data;
62  int ret, ts_start, ts_end;
63  AVBPrint buf;
64  const char *ptr = avpkt->data;
65  const char *end;
66 
67  if (!ptr || avpkt->size < 2)
68  return AVERROR_INVALIDDATA;
69 
70  /*
71  * A packet of size two with value zero is an empty subtitle
72  * used to mark the end of the previous non-empty subtitle.
73  * We can just drop them here as we have duration information
74  * already. If the value is non-zero, then it's technically a
75  * bad packet.
76  */
77  if (avpkt->size == 2)
78  return AV_RB16(ptr) == 0 ? 0 : AVERROR_INVALIDDATA;
79 
80  /*
81  * The first two bytes of the packet are the length of the text string
82  * In complex cases, there are style descriptors appended to the string
83  * so we can't just assume the packet size is the string size.
84  */
85  end = ptr + FFMIN(2 + AV_RB16(ptr), avpkt->size);
86  ptr += 2;
87 
88  ts_start = av_rescale_q(avpkt->pts,
89  avctx->time_base,
90  (AVRational){1,100});
91  ts_end = av_rescale_q(avpkt->pts + avpkt->duration,
92  avctx->time_base,
93  (AVRational){1,100});
94 
95  // Note that the spec recommends lines be no longer than 2048 characters.
97  text_to_ass(&buf, ptr, end);
98  ret = ff_ass_add_rect_bprint(sub, &buf, ts_start, ts_end-ts_start);
99  av_bprint_finalize(&buf, NULL);
100  if (ret < 0)
101  return ret;
102  *got_sub_ptr = sub->num_rects > 0;
103  return avpkt->size;
104 }
105 
107  .name = "mov_text",
108  .long_name = NULL_IF_CONFIG_SMALL("3GPP Timed Text subtitle"),
109  .type = AVMEDIA_TYPE_SUBTITLE,
110  .id = AV_CODEC_ID_MOV_TEXT,
111  .init = mov_text_init,
112  .decode = mov_text_decode_frame,
113 };