2 * Escape 124 Video Decoder
3 * Copyright (C) 2008 Eli Friedman (eli.friedman@gmail.com)
5 * This file is part of FFmpeg.
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.
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.
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
24 #define ALT_BITSTREAM_READER_LE
27 typedef union MacroBlock {
32 typedef union SuperBlock {
34 uint32_t pixels32[32];
37 typedef struct CodeBook {
43 typedef struct Escape124Context {
46 unsigned num_superblocks;
48 CodeBook codebooks[3];
51 static int can_safely_read(GetBitContext* gb, int bits) {
52 return get_bits_count(gb) + bits <= gb->size_in_bits;
56 * Initialize the decoder
57 * @param avctx decoder context
58 * @return 0 success, negative on error
60 static av_cold int escape124_decode_init(AVCodecContext *avctx)
62 Escape124Context *s = avctx->priv_data;
64 avcodec_get_frame_defaults(&s->frame);
65 avctx->pix_fmt = PIX_FMT_RGB555;
67 s->num_superblocks = ((unsigned)avctx->width / 8) *
68 ((unsigned)avctx->height / 8);
73 static av_cold int escape124_decode_close(AVCodecContext *avctx)
76 Escape124Context *s = avctx->priv_data;
78 for (i = 0; i < 3; i++)
79 av_free(s->codebooks[i].blocks);
82 avctx->release_buffer(avctx, &s->frame);
87 static CodeBook unpack_codebook(GetBitContext* gb, unsigned depth,
93 if (!can_safely_read(gb, size * 34))
96 if (size >= INT_MAX / sizeof(MacroBlock))
98 cb.blocks = av_malloc(size ? size * sizeof(MacroBlock) : 1);
104 for (i = 0; i < size; i++) {
105 unsigned mask_bits = get_bits(gb, 4);
106 unsigned color0 = get_bits(gb, 15);
107 unsigned color1 = get_bits(gb, 15);
109 for (j = 0; j < 4; j++) {
110 if (mask_bits & (1 << j))
111 cb.blocks[i].pixels[j] = color1;
113 cb.blocks[i].pixels[j] = color0;
119 static unsigned decode_skip_count(GetBitContext* gb)
122 // This function reads a maximum of 23 bits,
123 // which is within the padding space
124 if (!can_safely_read(gb, 1))
126 value = get_bits1(gb);
130 value += get_bits(gb, 3);
131 if (value != (1 + ((1 << 3) - 1)))
134 value += get_bits(gb, 7);
135 if (value != (1 + ((1 << 3) - 1)) + ((1 << 7) - 1))
138 return value + get_bits(gb, 12);
141 static MacroBlock decode_macroblock(Escape124Context* s, GetBitContext* gb,
142 int* codebook_index, int superblock_index)
144 // This function reads a maximum of 22 bits; the callers
145 // guard this function appropriately
146 unsigned block_index, depth;
149 static const char transitions[3][2] = { {2, 1}, {0, 2}, {1, 0} };
150 *codebook_index = transitions[*codebook_index][get_bits1(gb)];
153 depth = s->codebooks[*codebook_index].depth;
155 // depth = 0 means that this shouldn't read any bits;
156 // in theory, this is the same as get_bits(gb, 0), but
157 // that doesn't actually work.
158 block_index = depth ? get_bits(gb, depth) : 0;
160 if (*codebook_index == 1) {
161 block_index += superblock_index << s->codebooks[1].depth;
164 // This condition can occur with invalid bitstreams and
165 // *codebook_index == 2
166 if (block_index >= s->codebooks[*codebook_index].size)
167 return (MacroBlock) { { 0 } };
169 return s->codebooks[*codebook_index].blocks[block_index];
172 static void insert_mb_into_sb(SuperBlock* sb, MacroBlock mb, unsigned index) {
173 // Formula: ((index / 4) * 16 + (index % 4) * 2) / 2
174 uint32_t *dst = sb->pixels32 + index + (index & -4);
176 // This technically violates C99 aliasing rules, but it should be safe.
177 dst[0] = mb.pixels32[0];
178 dst[4] = mb.pixels32[1];
181 static void copy_superblock(uint16_t* dest, unsigned dest_stride,
182 uint16_t* src, unsigned src_stride)
186 for (y = 0; y < 8; y++)
187 memcpy(dest + y * dest_stride, src + y * src_stride,
188 sizeof(uint16_t) * 8);
190 for (y = 0; y < 8; y++)
191 memset(dest + y * dest_stride, 0, sizeof(uint16_t) * 8);
194 static const uint16_t mask_matrix[] = {0x1, 0x2, 0x10, 0x20,
195 0x4, 0x8, 0x40, 0x80,
196 0x100, 0x200, 0x1000, 0x2000,
197 0x400, 0x800, 0x4000, 0x8000};
199 static int escape124_decode_frame(AVCodecContext *avctx,
200 void *data, int *data_size,
203 const uint8_t *buf = avpkt->data;
204 int buf_size = avpkt->size;
205 Escape124Context *s = avctx->priv_data;
208 unsigned frame_flags, frame_size;
211 unsigned superblock_index, cb_index = 1,
212 superblock_col_index = 0,
213 superblocks_per_row = avctx->width / 8, skip = -1;
215 uint16_t* old_frame_data, *new_frame_data;
216 unsigned old_stride, new_stride;
219 avcodec_get_frame_defaults(&new_frame);
221 init_get_bits(&gb, buf, buf_size * 8);
223 // This call also guards the potential depth reads for the
224 // codebook unpacking.
225 if (!can_safely_read(&gb, 64))
228 frame_flags = get_bits_long(&gb, 32);
229 frame_size = get_bits_long(&gb, 32);
231 // Leave last frame unchanged
232 // FIXME: Is this necessary? I haven't seen it in any real samples
233 if (!(frame_flags & 0x114) || !(frame_flags & 0x7800000)) {
234 av_log(NULL, AV_LOG_DEBUG, "Skipping frame\n");
236 *data_size = sizeof(AVFrame);
237 *(AVFrame*)data = s->frame;
242 for (i = 0; i < 3; i++) {
243 if (frame_flags & (1 << (17 + i))) {
244 unsigned cb_depth, cb_size;
246 // This codebook can be cut off at places other than
247 // powers of 2, leaving some of the entries undefined.
248 cb_size = get_bits_long(&gb, 20);
249 cb_depth = av_log2(cb_size - 1) + 1;
251 cb_depth = get_bits(&gb, 4);
253 // This is the most basic codebook: pow(2,depth) entries
254 // for a depth-length key
255 cb_size = 1 << cb_depth;
257 // This codebook varies per superblock
258 // FIXME: I don't think this handles integer overflow
260 cb_size = s->num_superblocks << cb_depth;
263 av_free(s->codebooks[i].blocks);
264 s->codebooks[i] = unpack_codebook(&gb, cb_depth, cb_size);
265 if (!s->codebooks[i].blocks)
270 new_frame.reference = 3;
271 if (avctx->get_buffer(avctx, &new_frame)) {
272 av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
276 new_frame_data = (uint16_t*)new_frame.data[0];
277 new_stride = new_frame.linesize[0] / 2;
278 old_frame_data = (uint16_t*)s->frame.data[0];
279 old_stride = s->frame.linesize[0] / 2;
281 for (superblock_index = 0; superblock_index < s->num_superblocks;
282 superblock_index++) {
285 unsigned multi_mask = 0;
288 // Note that this call will make us skip the rest of the blocks
289 // if the frame prematurely ends
290 skip = decode_skip_count(&gb);
294 copy_superblock(new_frame_data, new_stride,
295 old_frame_data, old_stride);
297 copy_superblock(sb.pixels, 8,
298 old_frame_data, old_stride);
300 while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
302 mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
303 mask = get_bits(&gb, 16);
305 for (i = 0; i < 16; i++) {
306 if (mask & mask_matrix[i]) {
307 insert_mb_into_sb(&sb, mb, i);
312 if (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
313 unsigned inv_mask = get_bits(&gb, 4);
314 for (i = 0; i < 4; i++) {
315 if (inv_mask & (1 << i)) {
316 multi_mask ^= 0xF << i*4;
318 multi_mask ^= get_bits(&gb, 4) << i*4;
322 for (i = 0; i < 16; i++) {
323 if (multi_mask & mask_matrix[i]) {
324 if (!can_safely_read(&gb, 1))
326 mb = decode_macroblock(s, &gb, &cb_index,
328 insert_mb_into_sb(&sb, mb, i);
331 } else if (frame_flags & (1 << 16)) {
332 while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
333 mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
334 insert_mb_into_sb(&sb, mb, get_bits(&gb, 4));
338 copy_superblock(new_frame_data, new_stride, sb.pixels, 8);
341 superblock_col_index++;
345 if (superblock_col_index == superblocks_per_row) {
346 new_frame_data += new_stride * 8 - superblocks_per_row * 8;
348 old_frame_data += old_stride * 8 - superblocks_per_row * 8;
349 superblock_col_index = 0;
354 av_log(NULL, AV_LOG_DEBUG,
355 "Escape sizes: %i, %i, %i\n",
356 frame_size, buf_size, get_bits_count(&gb) / 8);
358 if (s->frame.data[0])
359 avctx->release_buffer(avctx, &s->frame);
361 *(AVFrame*)data = s->frame = new_frame;
362 *data_size = sizeof(AVFrame);
368 AVCodec ff_escape124_decoder = {
370 .type = AVMEDIA_TYPE_VIDEO,
371 .id = CODEC_ID_ESCAPE124,
372 .priv_data_size = sizeof(Escape124Context),
373 .init = escape124_decode_init,
374 .close = escape124_decode_close,
375 .decode = escape124_decode_frame,
376 .capabilities = CODEC_CAP_DR1,
377 .long_name = NULL_IF_CONFIG_SMALL("Escape 124"),