xsubdec.c
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1 /*
2  * XSUB subtitle decoder
3  * Copyright (c) 2007 Reimar Döffinger
4  *
5  * This file is part of Libav.
6  *
7  * Libav 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  * Libav 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 Libav; 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 = 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, rlelen, i;
57  int64_t packet_time = 0;
58  GetBitContext gb;
59 
60  memset(sub, 0, sizeof(*sub));
61 
62  // check that at least header fits
63  if (buf_size < 27 + 7 * 2 + 4 * 3) {
64  av_log(avctx, AV_LOG_ERROR, "coded frame too small\n");
65  return -1;
66  }
67 
68  // read start and end time
69  if (buf[0] != '[' || buf[13] != '-' || buf[26] != ']') {
70  av_log(avctx, AV_LOG_ERROR, "invalid time code\n");
71  return -1;
72  }
73  if (avpkt->pts != AV_NOPTS_VALUE)
74  packet_time = av_rescale_q(avpkt->pts, AV_TIME_BASE_Q, (AVRational){1, 1000});
75  sub->start_display_time = parse_timecode(buf + 1, packet_time);
76  sub->end_display_time = parse_timecode(buf + 14, packet_time);
77  buf += 27;
78 
79  // read header
80  w = bytestream_get_le16(&buf);
81  h = bytestream_get_le16(&buf);
82  if (av_image_check_size(w, h, 0, avctx) < 0)
83  return -1;
84  x = bytestream_get_le16(&buf);
85  y = bytestream_get_le16(&buf);
86  // skip bottom right position, it gives no new information
87  bytestream_get_le16(&buf);
88  bytestream_get_le16(&buf);
89  rlelen = bytestream_get_le16(&buf);
90 
91  // allocate sub and set values
92  sub->rects = av_mallocz(sizeof(*sub->rects));
93  sub->rects[0] = av_mallocz(sizeof(*sub->rects[0]));
94  sub->num_rects = 1;
95  sub->rects[0]->x = x; sub->rects[0]->y = y;
96  sub->rects[0]->w = w; sub->rects[0]->h = h;
97  sub->rects[0]->type = SUBTITLE_BITMAP;
98  sub->rects[0]->pict.linesize[0] = w;
99  sub->rects[0]->pict.data[0] = av_malloc(w * h);
100  sub->rects[0]->nb_colors = 4;
101  sub->rects[0]->pict.data[1] = av_mallocz(AVPALETTE_SIZE);
102 
103  // read palette
104  for (i = 0; i < sub->rects[0]->nb_colors; i++)
105  ((uint32_t*)sub->rects[0]->pict.data[1])[i] = bytestream_get_be24(&buf);
106  // make all except background (first entry) non-transparent
107  for (i = 1; i < sub->rects[0]->nb_colors; i++)
108  ((uint32_t*)sub->rects[0]->pict.data[1])[i] |= 0xff000000;
109 
110  // process RLE-compressed data
111  rlelen = FFMIN(rlelen, buf_end - buf);
112  init_get_bits(&gb, buf, rlelen * 8);
113  bitmap = sub->rects[0]->pict.data[0];
114  for (y = 0; y < h; y++) {
115  // interlaced: do odd lines
116  if (y == (h + 1) / 2) bitmap = sub->rects[0]->pict.data[0] + w;
117  for (x = 0; x < w; ) {
118  int log2 = ff_log2_tab[show_bits(&gb, 8)];
119  int run = get_bits(&gb, 14 - 4 * (log2 >> 1));
120  int color = get_bits(&gb, 2);
121  run = FFMIN(run, w - x);
122  // run length 0 means till end of row
123  if (!run) run = w - x;
124  memset(bitmap, color, run);
125  bitmap += run;
126  x += run;
127  }
128  // interlaced, skip every second line
129  bitmap += w;
130  align_get_bits(&gb);
131  }
132  *data_size = 1;
133  return buf_size;
134 }
135 
137  .name = "xsub",
138  .type = AVMEDIA_TYPE_SUBTITLE,
139  .id = CODEC_ID_XSUB,
140  .init = decode_init,
141  .decode = decode_frame,
142  .long_name = NULL_IF_CONFIG_SMALL("XSUB"),
143 };