escape124.c
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1 /*
2  * Escape 124 Video Decoder
3  * Copyright (C) 2008 Eli Friedman (eli.friedman@gmail.com)
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 "avcodec.h"
23 
24 #define BITSTREAM_READER_LE
25 #include "get_bits.h"
26 
27 typedef union MacroBlock {
28  uint16_t pixels[4];
29  uint32_t pixels32[2];
30 } MacroBlock;
31 
32 typedef union SuperBlock {
33  uint16_t pixels[64];
34  uint32_t pixels32[32];
35 } SuperBlock;
36 
37 typedef struct CodeBook {
38  unsigned depth;
39  unsigned size;
41 } CodeBook;
42 
43 typedef struct Escape124Context {
45 
46  unsigned num_superblocks;
47 
50 
51 static int can_safely_read(GetBitContext* gb, int bits) {
52  return get_bits_left(gb) >= bits;
53 }
54 
61 {
62  Escape124Context *s = avctx->priv_data;
63 
64  avctx->pix_fmt = PIX_FMT_RGB555;
65 
66  s->num_superblocks = ((unsigned)avctx->width / 8) *
67  ((unsigned)avctx->height / 8);
68 
69  return 0;
70 }
71 
73 {
74  unsigned i;
75  Escape124Context *s = avctx->priv_data;
76 
77  for (i = 0; i < 3; i++)
78  av_free(s->codebooks[i].blocks);
79 
80  if (s->frame.data[0])
81  avctx->release_buffer(avctx, &s->frame);
82 
83  return 0;
84 }
85 
87  unsigned size)
88 {
89  unsigned i, j;
90  CodeBook cb = { 0 };
91 
92  if (!can_safely_read(gb, size * 34))
93  return cb;
94 
95  if (size >= INT_MAX / sizeof(MacroBlock))
96  return cb;
97  cb.blocks = av_malloc(size ? size * sizeof(MacroBlock) : 1);
98  if (!cb.blocks)
99  return cb;
100 
101  cb.depth = depth;
102  cb.size = size;
103  for (i = 0; i < size; i++) {
104  unsigned mask_bits = get_bits(gb, 4);
105  unsigned color0 = get_bits(gb, 15);
106  unsigned color1 = get_bits(gb, 15);
107 
108  for (j = 0; j < 4; j++) {
109  if (mask_bits & (1 << j))
110  cb.blocks[i].pixels[j] = color1;
111  else
112  cb.blocks[i].pixels[j] = color0;
113  }
114  }
115  return cb;
116 }
117 
118 static unsigned decode_skip_count(GetBitContext* gb)
119 {
120  unsigned value;
121  // This function reads a maximum of 23 bits,
122  // which is within the padding space
123  if (!can_safely_read(gb, 1))
124  return -1;
125  value = get_bits1(gb);
126  if (!value)
127  return value;
128 
129  value += get_bits(gb, 3);
130  if (value != (1 + ((1 << 3) - 1)))
131  return value;
132 
133  value += get_bits(gb, 7);
134  if (value != (1 + ((1 << 3) - 1)) + ((1 << 7) - 1))
135  return value;
136 
137  return value + get_bits(gb, 12);
138 }
139 
141  int* codebook_index, int superblock_index)
142 {
143  // This function reads a maximum of 22 bits; the callers
144  // guard this function appropriately
145  unsigned block_index, depth;
146 
147  if (get_bits1(gb)) {
148  static const char transitions[3][2] = { {2, 1}, {0, 2}, {1, 0} };
149  *codebook_index = transitions[*codebook_index][get_bits1(gb)];
150  }
151 
152  depth = s->codebooks[*codebook_index].depth;
153 
154  // depth = 0 means that this shouldn't read any bits;
155  // in theory, this is the same as get_bits(gb, 0), but
156  // that doesn't actually work.
157  block_index = depth ? get_bits(gb, depth) : 0;
158 
159  if (*codebook_index == 1) {
160  block_index += superblock_index << s->codebooks[1].depth;
161  }
162 
163  // This condition can occur with invalid bitstreams and
164  // *codebook_index == 2
165  if (block_index >= s->codebooks[*codebook_index].size)
166  return (MacroBlock) { { 0 } };
167 
168  return s->codebooks[*codebook_index].blocks[block_index];
169 }
170 
171 static void insert_mb_into_sb(SuperBlock* sb, MacroBlock mb, unsigned index) {
172  // Formula: ((index / 4) * 16 + (index % 4) * 2) / 2
173  uint32_t *dst = sb->pixels32 + index + (index & -4);
174 
175  // This technically violates C99 aliasing rules, but it should be safe.
176  dst[0] = mb.pixels32[0];
177  dst[4] = mb.pixels32[1];
178 }
179 
180 static void copy_superblock(uint16_t* dest, unsigned dest_stride,
181  uint16_t* src, unsigned src_stride)
182 {
183  unsigned y;
184  if (src)
185  for (y = 0; y < 8; y++)
186  memcpy(dest + y * dest_stride, src + y * src_stride,
187  sizeof(uint16_t) * 8);
188  else
189  for (y = 0; y < 8; y++)
190  memset(dest + y * dest_stride, 0, sizeof(uint16_t) * 8);
191 }
192 
193 static const uint16_t mask_matrix[] = {0x1, 0x2, 0x10, 0x20,
194  0x4, 0x8, 0x40, 0x80,
195  0x100, 0x200, 0x1000, 0x2000,
196  0x400, 0x800, 0x4000, 0x8000};
197 
199  void *data, int *data_size,
200  AVPacket *avpkt)
201 {
202  const uint8_t *buf = avpkt->data;
203  int buf_size = avpkt->size;
204  Escape124Context *s = avctx->priv_data;
205 
206  GetBitContext gb;
207  unsigned frame_flags, frame_size;
208  unsigned i;
209 
210  unsigned superblock_index, cb_index = 1,
211  superblock_col_index = 0,
212  superblocks_per_row = avctx->width / 8, skip = -1;
213 
214  uint16_t* old_frame_data, *new_frame_data;
215  unsigned old_stride, new_stride;
216 
217  AVFrame new_frame = { { 0 } };
218 
219  init_get_bits(&gb, buf, buf_size * 8);
220 
221  // This call also guards the potential depth reads for the
222  // codebook unpacking.
223  if (!can_safely_read(&gb, 64))
224  return -1;
225 
226  frame_flags = get_bits_long(&gb, 32);
227  frame_size = get_bits_long(&gb, 32);
228 
229  // Leave last frame unchanged
230  // FIXME: Is this necessary? I haven't seen it in any real samples
231  if (!(frame_flags & 0x114) || !(frame_flags & 0x7800000)) {
232  av_log(NULL, AV_LOG_DEBUG, "Skipping frame\n");
233 
234  *data_size = sizeof(AVFrame);
235  *(AVFrame*)data = s->frame;
236 
237  return frame_size;
238  }
239 
240  for (i = 0; i < 3; i++) {
241  if (frame_flags & (1 << (17 + i))) {
242  unsigned cb_depth, cb_size;
243  if (i == 2) {
244  // This codebook can be cut off at places other than
245  // powers of 2, leaving some of the entries undefined.
246  cb_size = get_bits_long(&gb, 20);
247  cb_depth = av_log2(cb_size - 1) + 1;
248  } else {
249  cb_depth = get_bits(&gb, 4);
250  if (i == 0) {
251  // This is the most basic codebook: pow(2,depth) entries
252  // for a depth-length key
253  cb_size = 1 << cb_depth;
254  } else {
255  // This codebook varies per superblock
256  // FIXME: I don't think this handles integer overflow
257  // properly
258  cb_size = s->num_superblocks << cb_depth;
259  }
260  }
261  av_free(s->codebooks[i].blocks);
262  s->codebooks[i] = unpack_codebook(&gb, cb_depth, cb_size);
263  if (!s->codebooks[i].blocks)
264  return -1;
265  }
266  }
267 
268  new_frame.reference = 3;
269  if (avctx->get_buffer(avctx, &new_frame)) {
270  av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
271  return -1;
272  }
273 
274  new_frame_data = (uint16_t*)new_frame.data[0];
275  new_stride = new_frame.linesize[0] / 2;
276  old_frame_data = (uint16_t*)s->frame.data[0];
277  old_stride = s->frame.linesize[0] / 2;
278 
279  for (superblock_index = 0; superblock_index < s->num_superblocks;
280  superblock_index++) {
281  MacroBlock mb;
282  SuperBlock sb;
283  unsigned multi_mask = 0;
284 
285  if (skip == -1) {
286  // Note that this call will make us skip the rest of the blocks
287  // if the frame prematurely ends
288  skip = decode_skip_count(&gb);
289  }
290 
291  if (skip) {
292  copy_superblock(new_frame_data, new_stride,
293  old_frame_data, old_stride);
294  } else {
295  copy_superblock(sb.pixels, 8,
296  old_frame_data, old_stride);
297 
298  while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
299  unsigned mask;
300  mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
301  mask = get_bits(&gb, 16);
302  multi_mask |= mask;
303  for (i = 0; i < 16; i++) {
304  if (mask & mask_matrix[i]) {
305  insert_mb_into_sb(&sb, mb, i);
306  }
307  }
308  }
309 
310  if (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
311  unsigned inv_mask = get_bits(&gb, 4);
312  for (i = 0; i < 4; i++) {
313  if (inv_mask & (1 << i)) {
314  multi_mask ^= 0xF << i*4;
315  } else {
316  multi_mask ^= get_bits(&gb, 4) << i*4;
317  }
318  }
319 
320  for (i = 0; i < 16; i++) {
321  if (multi_mask & mask_matrix[i]) {
322  if (!can_safely_read(&gb, 1))
323  break;
324  mb = decode_macroblock(s, &gb, &cb_index,
325  superblock_index);
326  insert_mb_into_sb(&sb, mb, i);
327  }
328  }
329  } else if (frame_flags & (1 << 16)) {
330  while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
331  mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
332  insert_mb_into_sb(&sb, mb, get_bits(&gb, 4));
333  }
334  }
335 
336  copy_superblock(new_frame_data, new_stride, sb.pixels, 8);
337  }
338 
339  superblock_col_index++;
340  new_frame_data += 8;
341  if (old_frame_data)
342  old_frame_data += 8;
343  if (superblock_col_index == superblocks_per_row) {
344  new_frame_data += new_stride * 8 - superblocks_per_row * 8;
345  if (old_frame_data)
346  old_frame_data += old_stride * 8 - superblocks_per_row * 8;
347  superblock_col_index = 0;
348  }
349  skip--;
350  }
351 
353  "Escape sizes: %i, %i, %i\n",
354  frame_size, buf_size, get_bits_count(&gb) / 8);
355 
356  if (s->frame.data[0])
357  avctx->release_buffer(avctx, &s->frame);
358 
359  *(AVFrame*)data = s->frame = new_frame;
360  *data_size = sizeof(AVFrame);
361 
362  return frame_size;
363 }
364 
365 
367  .name = "escape124",
368  .type = AVMEDIA_TYPE_VIDEO,
369  .id = CODEC_ID_ESCAPE124,
370  .priv_data_size = sizeof(Escape124Context),
374  .capabilities = CODEC_CAP_DR1,
375  .long_name = NULL_IF_CONFIG_SMALL("Escape 124"),
376 };
377