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xsubdec.c
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1 /*
2  * XSUB subtitle decoder
3  * Copyright (c) 2007 Reimar Döffinger
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 "libavutil/mathematics.h"
23 #include "libavutil/imgutils.h"
24 #include "avcodec.h"
25 #include "get_bits.h"
26 #include "bytestream.h"
27 
28 static av_cold int decode_init(AVCodecContext *avctx) {
29  avctx->pix_fmt = AV_PIX_FMT_PAL8;
30  return 0;
31 }
32 
33 static const uint8_t tc_offsets[9] = { 0, 1, 3, 4, 6, 7, 9, 10, 11 };
34 static const uint8_t tc_muls[9] = { 10, 6, 10, 6, 10, 10, 10, 10, 1 };
35 
36 static int64_t parse_timecode(const uint8_t *buf, int64_t packet_time) {
37  int i;
38  int64_t ms = 0;
39  if (buf[2] != ':' || buf[5] != ':' || buf[8] != '.')
40  return AV_NOPTS_VALUE;
41  for (i = 0; i < sizeof(tc_offsets); i++) {
42  uint8_t c = buf[tc_offsets[i]] - '0';
43  if (c > 9) return AV_NOPTS_VALUE;
44  ms = (ms + c) * tc_muls[i];
45  }
46  return ms - packet_time;
47 }
48 
49 static int decode_frame(AVCodecContext *avctx, void *data, int *data_size,
50  AVPacket *avpkt) {
51  const uint8_t *buf = avpkt->data;
52  int buf_size = avpkt->size;
53  AVSubtitle *sub = data;
54  const uint8_t *buf_end = buf + buf_size;
55  uint8_t *bitmap;
56  int w, h, x, y, i;
57  int64_t packet_time = 0;
58  GetBitContext gb;
59  int has_alpha = avctx->codec_tag == MKTAG('D','X','S','A');
60 
61  // check that at least header fits
62  if (buf_size < 27 + 7 * 2 + 4 * 3) {
63  av_log(avctx, AV_LOG_ERROR, "coded frame size %d too small\n", buf_size);
64  return -1;
65  }
66 
67  // read start and end time
68  if (buf[0] != '[' || buf[13] != '-' || buf[26] != ']') {
69  av_log(avctx, AV_LOG_ERROR, "invalid time code\n");
70  return -1;
71  }
72  if (avpkt->pts != AV_NOPTS_VALUE)
73  packet_time = av_rescale_q(avpkt->pts, AV_TIME_BASE_Q, (AVRational){1, 1000});
74  sub->start_display_time = parse_timecode(buf + 1, packet_time);
75  sub->end_display_time = parse_timecode(buf + 14, packet_time);
76  buf += 27;
77 
78  // read header
79  w = bytestream_get_le16(&buf);
80  h = bytestream_get_le16(&buf);
81  if (av_image_check_size(w, h, 0, avctx) < 0)
82  return -1;
83  x = bytestream_get_le16(&buf);
84  y = bytestream_get_le16(&buf);
85  // skip bottom right position, it gives no new information
86  bytestream_get_le16(&buf);
87  bytestream_get_le16(&buf);
88  // The following value is supposed to indicate the start offset
89  // (relative to the palette) of the data for the second field,
90  // however there are files in which it has a bogus value and thus
91  // we just ignore it
92  bytestream_get_le16(&buf);
93 
94  // allocate sub and set values
95  sub->rects = av_mallocz(sizeof(*sub->rects));
96  sub->rects[0] = av_mallocz(sizeof(*sub->rects[0]));
97  sub->num_rects = 1;
98  sub->rects[0]->x = x; sub->rects[0]->y = y;
99  sub->rects[0]->w = w; sub->rects[0]->h = h;
100  sub->rects[0]->type = SUBTITLE_BITMAP;
101  sub->rects[0]->pict.linesize[0] = w;
102  sub->rects[0]->pict.data[0] = av_malloc(w * h);
103  sub->rects[0]->nb_colors = 4;
104  sub->rects[0]->pict.data[1] = av_mallocz(AVPALETTE_SIZE);
105 
106  // read palette
107  for (i = 0; i < sub->rects[0]->nb_colors; i++)
108  ((uint32_t*)sub->rects[0]->pict.data[1])[i] = bytestream_get_be24(&buf);
109  // make all except background (first entry) non-transparent
110  for (i = 0; i < sub->rects[0]->nb_colors; i++)
111  ((uint32_t*)sub->rects[0]->pict.data[1])[i] |= (has_alpha ? *buf++ : (i ? 0xff : 0)) << 24;
112 
113  // process RLE-compressed data
114  init_get_bits(&gb, buf, (buf_end - buf) * 8);
115  bitmap = sub->rects[0]->pict.data[0];
116  for (y = 0; y < h; y++) {
117  // interlaced: do odd lines
118  if (y == (h + 1) / 2) bitmap = sub->rects[0]->pict.data[0] + w;
119  for (x = 0; x < w; ) {
120  int log2 = ff_log2_tab[show_bits(&gb, 8)];
121  int run = get_bits(&gb, 14 - 4 * (log2 >> 1));
122  int color = get_bits(&gb, 2);
123  run = FFMIN(run, w - x);
124  // run length 0 means till end of row
125  if (!run) run = w - x;
126  memset(bitmap, color, run);
127  bitmap += run;
128  x += run;
129  }
130  // interlaced, skip every second line
131  bitmap += w;
132  align_get_bits(&gb);
133  }
134  *data_size = 1;
135  return buf_size;
136 }
137 
139  .name = "xsub",
140  .long_name = NULL_IF_CONFIG_SMALL("XSUB"),
141  .type = AVMEDIA_TYPE_SUBTITLE,
142  .id = AV_CODEC_ID_XSUB,
143  .init = decode_init,
144  .decode = decode_frame,
145 };