FFmpeg: libavcodec/h261dec.c Source File

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h261dec.c

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1 /*

2 * H261 decoder

5 *

6 * This file is part of FFmpeg.

7 *

8 * FFmpeg is free software; you can redistribute it and/or

9 * modify it under the terms of the GNU Lesser General Public

10 * License as published by the Free Software Foundation; either

11 * version 2.1 of the License, or (at your option) any later version.

12 *

13 * FFmpeg is distributed in the hope that it will be useful,

14 * but WITHOUT ANY WARRANTY; without even the implied warranty of

15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

16 * Lesser General Public License for more details.

17 *

18 * You should have received a copy of the GNU Lesser General Public

19 * License along with FFmpeg; if not, write to the Free Software

20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

21 */

23 /**

24 * @file

25 * H.261 decoder.

26 */

28 #include "libavutil/avassert.h"

29 #include "avcodec.h"

30 #include "mpegvideo.h"

31 #include "h263.h"

32 #include "h261.h"

34 #define H261_MBA_VLC_BITS 9

35 #define H261_MTYPE_VLC_BITS 6

36 #define H261_MV_VLC_BITS 7

37 #define H261_CBP_VLC_BITS 9

38 #define TCOEFF_VLC_BITS 9

39 #define MBA_STUFFING 33

40 #define MBA_STARTCODE 34

42 static VLC h261_mba_vlc;

43 static VLC h261_mtype_vlc;

44 static VLC h261_mv_vlc;

45 static VLC h261_cbp_vlc;

47 static av_cold void h261_decode_init_vlc(H261Context *h)

48 {

49 static int done = 0;

51 if (!done) {

52 done = 1;

53 INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,

54 ff_h261_mba_bits, 1, 1,

55 ff_h261_mba_code, 1, 1, 662);

56 INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,

57 ff_h261_mtype_bits, 1, 1,

58 ff_h261_mtype_code, 1, 1, 80);

59 INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,

60 &ff_h261_mv_tab[0][1], 2, 1,

61 &ff_h261_mv_tab[0][0], 2, 1, 144);

62 INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,

63 &ff_h261_cbp_tab[0][1], 2, 1,

64 &ff_h261_cbp_tab[0][0], 2, 1, 512);

65 INIT_VLC_RL(ff_h261_rl_tcoeff, 552);

66 }

67 }

69 static av_cold int h261_decode_init(AVCodecContext *avctx)

70 {

71 H261Context *h = avctx->priv_data;

72 MpegEncContext *const s = &h->s;

74 // set defaults

75 ff_MPV_decode_defaults(s);

76 s->avctx = avctx;

77 s->width = s->avctx->coded_width;

78 s->height = s->avctx->coded_height;

79 s->codec_id = s->avctx->codec->id;

80 s->out_format = FMT_H261;

81 s->low_delay = 1;

82 avctx->pix_fmt = AV_PIX_FMT_YUV420P;

83 s->codec_id = avctx->codec->id;

85 ff_h261_common_init();

86 h261_decode_init_vlc(h);

88 h->gob_start_code_skipped = 0;

90 return 0;

91 }

93 /**

94 * Decode the group of blocks header or slice header.

95 * @return <0 if an error occurred

96 */

97 static int h261_decode_gob_header(H261Context *h)

98 {

99 unsigned int val;

100 MpegEncContext *const s = &h->s;

101

102 if (!h->gob_start_code_skipped) {

103 /* Check for GOB Start Code */

104 val = show_bits(&s->gb, 15);

105 if (val)

106 return -1;

107

108 /* We have a GBSC */

109 skip_bits(&s->gb, 16);

110 }

111

112 h->gob_start_code_skipped = 0;

113

114 h->gob_number = get_bits(&s->gb, 4); /* GN */

115 s->qscale = get_bits(&s->gb, 5); /* GQUANT */

116

117 /* Check if gob_number is valid */

118 if (s->mb_height == 18) { // CIF

119 if ((h->gob_number <= 0) || (h->gob_number > 12))

120 return -1;

121 } else { // QCIF

122 if ((h->gob_number != 1) && (h->gob_number != 3) &&

123 (h->gob_number != 5))

124 return -1;

125 }

126

127 /* GEI */

128 while (get_bits1(&s->gb) != 0)

129 skip_bits(&s->gb, 8);

130

131 if (s->qscale == 0) {

132 av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");

133 if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))

134 return -1;

135 }

136

137 /* For the first transmitted macroblock in a GOB, MBA is the absolute

138 * address. For subsequent macroblocks, MBA is the difference between

139 * the absolute addresses of the macroblock and the last transmitted

140 * macroblock. */

141 h->current_mba = 0;

142 h->mba_diff = 0;

143

144 return 0;

145 }

146

147 /**

148 * Decode the group of blocks / video packet header.

149 * @return <0 if no resync found

150 */

151 static int h261_resync(H261Context *h)

152 {

153 MpegEncContext *const s = &h->s;

154 int left, ret;

155

156 if (h->gob_start_code_skipped) {

157 ret = h261_decode_gob_header(h);

158 if (ret >= 0)

159 return 0;

160 } else {

161 if (show_bits(&s->gb, 15) == 0) {

162 ret = h261_decode_gob_header(h);

163 if (ret >= 0)

164 return 0;

165 }

166 // OK, it is not where it is supposed to be ...

167 s->gb = s->last_resync_gb;

168 align_get_bits(&s->gb);

169 left = get_bits_left(&s->gb);

170

171 for (; left > 15 + 1 + 4 + 5; left -= 8) {

172 if (show_bits(&s->gb, 15) == 0) {

173 GetBitContext bak = s->gb;

174

175 ret = h261_decode_gob_header(h);

176 if (ret >= 0)

177 return 0;

178

179 s->gb = bak;

180 }

181 skip_bits(&s->gb, 8);

182 }

183 }

184

185 return -1;

186 }

187

188 /**

189 * Decode skipped macroblocks.

190 * @return 0

191 */

192 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)

193 {

194 MpegEncContext *const s = &h->s;

195 int i;

196

197 s->mb_intra = 0;

198

199 for (i = mba1; i < mba2; i++) {

200 int j, xy;

201

202 s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;

203 s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;

204 xy = s->mb_x + s->mb_y * s->mb_stride;

205 ff_init_block_index(s);

206 ff_update_block_index(s);

207

208 for (j = 0; j < 6; j++)

209 s->block_last_index[j] = -1;

210

211 s->mv_dir = MV_DIR_FORWARD;

212 s->mv_type = MV_TYPE_16X16;

213 s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;

214 s->mv[0][0][0] = 0;

215 s->mv[0][0][1] = 0;

216 s->mb_skipped = 1;

217 h->mtype &= ~MB_TYPE_H261_FIL;

218

219 ff_MPV_decode_mb(s, s->block);

220 }

221

222 return 0;

223 }

224

225 static const int mvmap[17] = {

226 0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16

227 };

228

229 static int decode_mv_component(GetBitContext *gb, int v)

230 {

231 int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);

232

233 /* check if mv_diff is valid */

234 if (mv_diff < 0)

235 return v;

236

237 mv_diff = mvmap[mv_diff];

238

239 if (mv_diff && !get_bits1(gb))

240 mv_diff = -mv_diff;

241

242 v += mv_diff;

243 if (v <= -16)

244 v += 32;

245 else if (v >= 16)

246 v -= 32;

247

248 return v;

249 }

250

251 /**

252 * Decode a macroblock.

253 * @return <0 if an error occurred

254 */

255 static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)

256 {

257 MpegEncContext *const s = &h->s;

258 int code, level, i, j, run;

259 RLTable *rl = &ff_h261_rl_tcoeff;

260 const uint8_t *scan_table;

261

262 /* For the variable length encoding there are two code tables, one being

263 * used for the first transmitted LEVEL in INTER, INTER + MC and

264 * INTER + MC + FIL blocks, the second for all other LEVELs except the

265 * first one in INTRA blocks which is fixed length coded with 8 bits.

266 * NOTE: The two code tables only differ in one VLC so we handle that

267 * manually. */

268 scan_table = s->intra_scantable.permutated;

269 if (s->mb_intra) {

270 /* DC coef */

271 level = get_bits(&s->gb, 8);

272 // 0 (00000000b) and -128 (10000000b) are FORBIDDEN

273 if ((level & 0x7F) == 0) {

274 av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",

275 level, s->mb_x, s->mb_y);

276 return -1;

277 }

278 /* The code 1000 0000 is not used, the reconstruction level of 1024

279 * being coded as 1111 1111. */

280 if (level == 255)

281 level = 128;

282 block[0] = level;

283 i = 1;

284 } else if (coded) {

285 // Run Level Code

286 // EOB Not possible for first level when cbp is available (that's why the table is different)

287 // 0 1 1s

288 // * * 0*

289 int check = show_bits(&s->gb, 2);

290 i = 0;

291 if (check & 0x2) {

292 skip_bits(&s->gb, 2);

293 block[0] = (check & 0x1) ? -1 : 1;

294 i = 1;

295 }

296 } else {

297 i = 0;

298 }

299 if (!coded) {

300 s->block_last_index[n] = i - 1;

301 return 0;

302 }

303 for (;;) {

304 code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);

305 if (code < 0) {

306 av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",

307 s->mb_x, s->mb_y);

308 return -1;

309 }

310 if (code == rl->n) {

311 /* escape */

312 /* The remaining combinations of (run, level) are encoded with a

313 * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits

314 * level. */

315 run = get_bits(&s->gb, 6);

316 level = get_sbits(&s->gb, 8);

317 } else if (code == 0) {

318 break;

319 } else {

320 run = rl->table_run[code];

321 level = rl->table_level[code];

322 if (get_bits1(&s->gb))

323 level = -level;

324 }

325 i += run;

326 if (i >= 64) {

327 av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",

328 s->mb_x, s->mb_y);

329 return -1;

330 }

331 j = scan_table[i];

332 block[j] = level;

333 i++;

334 }

335 s->block_last_index[n] = i - 1;

336 return 0;

337 }

338

339 static int h261_decode_mb(H261Context *h)

340 {

341 MpegEncContext *const s = &h->s;

342 int i, cbp, xy;

343

344 cbp = 63;

345 // Read mba

346 do {

347 h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,

348 H261_MBA_VLC_BITS, 2);

349

350 /* Check for slice end */

351 /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */

352 if (h->mba_diff == MBA_STARTCODE) { // start code

353 h->gob_start_code_skipped = 1;

354 return SLICE_END;

355 }

356 } while (h->mba_diff == MBA_STUFFING); // stuffing

357

358 if (h->mba_diff < 0) {

359 if (get_bits_left(&s->gb) <= 7)

360 return SLICE_END;

361

362 av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);

363 return SLICE_ERROR;

364 }

365

366 h->mba_diff += 1;

367 h->current_mba += h->mba_diff;

368

369 if (h->current_mba > MBA_STUFFING)

370 return SLICE_ERROR;

371

372 s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);

373 s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);

374 xy = s->mb_x + s->mb_y * s->mb_stride;

375 ff_init_block_index(s);

376 ff_update_block_index(s);

377

378 // Read mtype

379 h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);

380 if (h->mtype < 0) {

381 av_log(s->avctx, AV_LOG_ERROR, "illegal mtype %d\n", h->mtype);

382 return SLICE_ERROR;

383 }

384 h->mtype = ff_h261_mtype_map[h->mtype];

385

386 // Read mquant

387 if (IS_QUANT(h->mtype))

388 ff_set_qscale(s, get_bits(&s->gb, 5));

389

390 s->mb_intra = IS_INTRA4x4(h->mtype);

391

392 // Read mv

393 if (IS_16X16(h->mtype)) {

394 /* Motion vector data is included for all MC macroblocks. MVD is

395 * obtained from the macroblock vector by subtracting the vector

396 * of the preceding macroblock. For this calculation the vector

397 * of the preceding macroblock is regarded as zero in the

398 * following three situations:

399 * 1) evaluating MVD for macroblocks 1, 12 and 23;

400 * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;

401 * 3) MTYPE of the previous macroblock was not MC. */

402 if ((h->current_mba == 1) || (h->current_mba == 12) ||

403 (h->current_mba == 23) || (h->mba_diff != 1)) {

404 h->current_mv_x = 0;

405 h->current_mv_y = 0;

406 }

407

408 h->current_mv_x = decode_mv_component(&s->gb, h->current_mv_x);

409 h->current_mv_y = decode_mv_component(&s->gb, h->current_mv_y);

410 } else {

411 h->current_mv_x = 0;

412 h->current_mv_y = 0;

413 }

414

415 // Read cbp

416 if (HAS_CBP(h->mtype))

417 cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;

418

419 if (s->mb_intra) {

420 s->current_picture.mb_type[xy] = MB_TYPE_INTRA;

421 goto intra;

422 }

423

424 //set motion vectors

425 s->mv_dir = MV_DIR_FORWARD;

426 s->mv_type = MV_TYPE_16X16;

427 s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;

428 s->mv[0][0][0] = h->current_mv_x * 2; // gets divided by 2 in motion compensation

429 s->mv[0][0][1] = h->current_mv_y * 2;

430

431 intra:

432 /* decode each block */

433 if (s->mb_intra || HAS_CBP(h->mtype)) {

434 s->dsp.clear_blocks(s->block[0]);

435 for (i = 0; i < 6; i++) {

436 if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)

437 return SLICE_ERROR;

438 cbp += cbp;

439 }

440 } else {

441 for (i = 0; i < 6; i++)

442 s->block_last_index[i] = -1;

443 }

444

445 ff_MPV_decode_mb(s, s->block);

446

447 return SLICE_OK;

448 }

449

450 /**

451 * Decode the H.261 picture header.

452 * @return <0 if no startcode found

453 */

454 static int h261_decode_picture_header(H261Context *h)

455 {

456 MpegEncContext *const s = &h->s;

457 int format, i;

458 uint32_t startcode = 0;

459

460 for (i = get_bits_left(&s->gb); i > 24; i -= 1) {

461 startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;

462

463 if (startcode == 0x10)

464 break;

465 }

466

467 if (startcode != 0x10) {

468 av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");

469 return -1;

470 }

471

472 /* temporal reference */

473 i = get_bits(&s->gb, 5); /* picture timestamp */

474 if (i < (s->picture_number & 31))

475 i += 32;

476 s->picture_number = (s->picture_number & ~31) + i;

477

478 s->avctx->time_base = (AVRational) { 1001, 30000 };

479 s->current_picture.f.pts = s->picture_number;

480

481 /* PTYPE starts here */

482 skip_bits1(&s->gb); /* split screen off */

483 skip_bits1(&s->gb); /* camera off */

484 skip_bits1(&s->gb); /* freeze picture release off */

485

486 format = get_bits1(&s->gb);

487

488 // only 2 formats possible

489 if (format == 0) { // QCIF

490 s->width = 176;

491 s->height = 144;

492 s->mb_width = 11;

493 s->mb_height = 9;

494 } else { // CIF

495 s->width = 352;

496 s->height = 288;

497 s->mb_width = 22;

498 s->mb_height = 18;

499 }

500

501 s->mb_num = s->mb_width * s->mb_height;

502

503 skip_bits1(&s->gb); /* still image mode off */

504 skip_bits1(&s->gb); /* Reserved */

505

506 /* PEI */

507 while (get_bits1(&s->gb) != 0)

508 skip_bits(&s->gb, 8);

509

510 /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first

511 * frame, the codec crashes if it does not contain all I-blocks

512 * (e.g. when a packet is lost). */

513 s->pict_type = AV_PICTURE_TYPE_P;

514

515 h->gob_number = 0;

516 return 0;

517 }

518

519 static int h261_decode_gob(H261Context *h)

520 {

521 MpegEncContext *const s = &h->s;

522

523 ff_set_qscale(s, s->qscale);

524

525 /* decode mb's */

526 while (h->current_mba <= MBA_STUFFING) {

527 int ret;

528 /* DCT & quantize */

529 ret = h261_decode_mb(h);

530 if (ret < 0) {

531 if (ret == SLICE_END) {

532 h261_decode_mb_skipped(h, h->current_mba, 33);

533 return 0;

534 }

535 av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",

536 s->mb_x + s->mb_y * s->mb_stride);

537 return -1;

538 }

539

540 h261_decode_mb_skipped(h,

541 h->current_mba - h->mba_diff,

542 h->current_mba - 1);

543 }

544

545 return -1;

546 }

547

548 /**

549 * returns the number of bytes consumed for building the current frame

550 */

551 static int get_consumed_bytes(MpegEncContext *s, int buf_size)

552 {

553 int pos = get_bits_count(&s->gb) >> 3;

554 if (pos == 0)

555 pos = 1; // avoid infinite loops (i doubt that is needed but ...)

556 if (pos + 10 > buf_size)

557 pos = buf_size; // oops ;)

558

559 return pos;

560 }

561

562 static int h261_decode_frame(AVCodecContext *avctx, void *data,

563 int *got_frame, AVPacket *avpkt)

564 {

565 const uint8_t *buf = avpkt->data;

566 int buf_size = avpkt->size;

567 H261Context *h = avctx->priv_data;

568 MpegEncContext *s = &h->s;

569 int ret;

570 AVFrame *pict = data;

571

572 av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);

573 av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);

574 s->flags = avctx->flags;

575 s->flags2 = avctx->flags2;

576

577 h->gob_start_code_skipped = 0;

578

579 retry:

580 init_get_bits(&s->gb, buf, buf_size * 8);

581

582 if (!s->context_initialized)

583 // we need the IDCT permutaton for reading a custom matrix

584 if (ff_MPV_common_init(s) < 0)

585 return -1;

586

587 /* We need to set current_picture_ptr before reading the header,

588 * otherwise we cannot store anything in there. */

589 if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {

590 int i = ff_find_unused_picture(s, 0);

591 if (i < 0)

592 return i;

593 s->current_picture_ptr = &s->picture[i];

594 }

595

596 ret = h261_decode_picture_header(h);

597

598 /* skip if the header was thrashed */

599 if (ret < 0) {

600 av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");

601 return -1;

602 }

603

604 if (s->width != avctx->coded_width || s->height != avctx->coded_height) {

605 ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat

606 s->parse_context.buffer = 0;

607 ff_MPV_common_end(s);

608 s->parse_context = pc;

609 }

610 if (!s->context_initialized) {

611 avcodec_set_dimensions(avctx, s->width, s->height);

612

613 goto retry;

614 }

615

616 // for skipping the frame

617 s->current_picture.f.pict_type = s->pict_type;

618 s->current_picture.f.key_frame = s->pict_type == AV_PICTURE_TYPE_I;

619

620 if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||

621 (avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I) ||

622 avctx->skip_frame >= AVDISCARD_ALL)

623 return get_consumed_bytes(s, buf_size);

624

625 if (ff_MPV_frame_start(s, avctx) < 0)

626 return -1;

627

628 ff_mpeg_er_frame_start(s);

629

630 /* decode each macroblock */

631 s->mb_x = 0;

632 s->mb_y = 0;

633

634 while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {

635 if (h261_resync(h) < 0)

636 break;

637 h261_decode_gob(h);

638 }

639 ff_MPV_frame_end(s);

640

641 av_assert0(s->current_picture.f.pict_type == s->current_picture_ptr->f.pict_type);

642 av_assert0(s->current_picture.f.pict_type == s->pict_type);

643

644 if ((ret = av_frame_ref(pict, &s->current_picture_ptr->f)) < 0)

645 return ret;

646 ff_print_debug_info(s, s->current_picture_ptr, pict);

647

648 *got_frame = 1;

649

650 return get_consumed_bytes(s, buf_size);

651 }

652

653 static av_cold int h261_decode_end(AVCodecContext *avctx)

654 {

655 H261Context *h = avctx->priv_data;

656 MpegEncContext *s = &h->s;

657

658 ff_MPV_common_end(s);

659 return 0;

660 }

661

662 AVCodec ff_h261_decoder = {

663 .name = "h261",

664 .type = AVMEDIA_TYPE_VIDEO,

665 .id = AV_CODEC_ID_H261,

666 .priv_data_size = sizeof(H261Context),

667 .init = h261_decode_init,

668 .close = h261_decode_end,

669 .decode = h261_decode_frame,

670 .capabilities = CODEC_CAP_DR1,

671 .max_lowres = 3,

672 .long_name = NULL_IF_CONFIG_SMALL("H.261"),

673 };

Generated on Wed Jul 10 2013 23:47:58 for FFmpeg by doxygen 1.8.2