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h261dec.c
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1 /*
2  * H261 decoder
3  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
4  * Copyright (c) 2004 Maarten Daniels
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  */
22 
23 /**
24  * @file
25  * H.261 decoder.
26  */
27 
28 #include "libavutil/avassert.h"
29 #include "avcodec.h"
30 #include "mpeg_er.h"
31 #include "mpegutils.h"
32 #include "mpegvideo.h"
33 #include "h263.h"
34 #include "h261.h"
35 #include "internal.h"
36 
37 #define H261_MBA_VLC_BITS 9
38 #define H261_MTYPE_VLC_BITS 6
39 #define H261_MV_VLC_BITS 7
40 #define H261_CBP_VLC_BITS 9
41 #define TCOEFF_VLC_BITS 9
42 #define MBA_STUFFING 33
43 #define MBA_STARTCODE 34
44 
49 
51 {
52  static int done = 0;
53 
54  if (!done) {
55  done = 1;
56  INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
57  ff_h261_mba_bits, 1, 1,
58  ff_h261_mba_code, 1, 1, 662);
59  INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
60  ff_h261_mtype_bits, 1, 1,
61  ff_h261_mtype_code, 1, 1, 80);
62  INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
63  &ff_h261_mv_tab[0][1], 2, 1,
64  &ff_h261_mv_tab[0][0], 2, 1, 144);
65  INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
66  &ff_h261_cbp_tab[0][1], 2, 1,
67  &ff_h261_cbp_tab[0][0], 2, 1, 512);
69  }
70 }
71 
73 {
74  H261Context *h = avctx->priv_data;
75  MpegEncContext *const s = &h->s;
76 
77  // set defaults
79  s->avctx = avctx;
80  s->width = s->avctx->coded_width;
81  s->height = s->avctx->coded_height;
82  s->codec_id = s->avctx->codec->id;
83  s->out_format = FMT_H261;
84  s->low_delay = 1;
85  avctx->pix_fmt = AV_PIX_FMT_YUV420P;
86  s->codec_id = avctx->codec->id;
87 
90 
92 
93  return 0;
94 }
95 
96 /**
97  * Decode the group of blocks header or slice header.
98  * @return <0 if an error occurred
99  */
101 {
102  unsigned int val;
103  MpegEncContext *const s = &h->s;
104 
105  if (!h->gob_start_code_skipped) {
106  /* Check for GOB Start Code */
107  val = show_bits(&s->gb, 15);
108  if (val)
109  return -1;
110 
111  /* We have a GBSC */
112  skip_bits(&s->gb, 16);
113  }
114 
115  h->gob_start_code_skipped = 0;
116 
117  h->gob_number = get_bits(&s->gb, 4); /* GN */
118  s->qscale = get_bits(&s->gb, 5); /* GQUANT */
119 
120  /* Check if gob_number is valid */
121  if (s->mb_height == 18) { // CIF
122  if ((h->gob_number <= 0) || (h->gob_number > 12))
123  return -1;
124  } else { // QCIF
125  if ((h->gob_number != 1) && (h->gob_number != 3) &&
126  (h->gob_number != 5))
127  return -1;
128  }
129 
130  /* GEI */
131  if (skip_1stop_8data_bits(&s->gb) < 0)
132  return AVERROR_INVALIDDATA;
133 
134  if (s->qscale == 0) {
135  av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
137  return -1;
138  }
139 
140  /* For the first transmitted macroblock in a GOB, MBA is the absolute
141  * address. For subsequent macroblocks, MBA is the difference between
142  * the absolute addresses of the macroblock and the last transmitted
143  * macroblock. */
144  h->current_mba = 0;
145  h->mba_diff = 0;
146 
147  return 0;
148 }
149 
150 /**
151  * Decode the group of blocks / video packet header.
152  * @return <0 if no resync found
153  */
154 static int h261_resync(H261Context *h)
155 {
156  MpegEncContext *const s = &h->s;
157  int left, ret;
158 
159  if (h->gob_start_code_skipped) {
160  ret = h261_decode_gob_header(h);
161  if (ret >= 0)
162  return 0;
163  } else {
164  if (show_bits(&s->gb, 15) == 0) {
165  ret = h261_decode_gob_header(h);
166  if (ret >= 0)
167  return 0;
168  }
169  // OK, it is not where it is supposed to be ...
170  s->gb = s->last_resync_gb;
171  align_get_bits(&s->gb);
172  left = get_bits_left(&s->gb);
173 
174  for (; left > 15 + 1 + 4 + 5; left -= 8) {
175  if (show_bits(&s->gb, 15) == 0) {
176  GetBitContext bak = s->gb;
177 
178  ret = h261_decode_gob_header(h);
179  if (ret >= 0)
180  return 0;
181 
182  s->gb = bak;
183  }
184  skip_bits(&s->gb, 8);
185  }
186  }
187 
188  return -1;
189 }
190 
191 /**
192  * Decode skipped macroblocks.
193  * @return 0
194  */
195 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)
196 {
197  MpegEncContext *const s = &h->s;
198  int i;
199 
200  s->mb_intra = 0;
201 
202  for (i = mba1; i < mba2; i++) {
203  int j, xy;
204 
205  s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;
206  s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;
207  xy = s->mb_x + s->mb_y * s->mb_stride;
210 
211  for (j = 0; j < 6; j++)
212  s->block_last_index[j] = -1;
213 
214  s->mv_dir = MV_DIR_FORWARD;
215  s->mv_type = MV_TYPE_16X16;
217  s->mv[0][0][0] = 0;
218  s->mv[0][0][1] = 0;
219  s->mb_skipped = 1;
220  h->mtype &= ~MB_TYPE_H261_FIL;
221 
222  ff_mpv_decode_mb(s, s->block);
223  }
224 
225  return 0;
226 }
227 
228 static const int mvmap[17] = {
229  0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16
230 };
231 
232 static int decode_mv_component(GetBitContext *gb, int v)
233 {
234  int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
235 
236  /* check if mv_diff is valid */
237  if (mv_diff < 0)
238  return v;
239 
240  mv_diff = mvmap[mv_diff];
241 
242  if (mv_diff && !get_bits1(gb))
243  mv_diff = -mv_diff;
244 
245  v += mv_diff;
246  if (v <= -16)
247  v += 32;
248  else if (v >= 16)
249  v -= 32;
250 
251  return v;
252 }
253 
254 /**
255  * Decode a macroblock.
256  * @return <0 if an error occurred
257  */
258 static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)
259 {
260  MpegEncContext *const s = &h->s;
261  int code, level, i, j, run;
262  RLTable *rl = &ff_h261_rl_tcoeff;
263  const uint8_t *scan_table;
264 
265  /* For the variable length encoding there are two code tables, one being
266  * used for the first transmitted LEVEL in INTER, INTER + MC and
267  * INTER + MC + FIL blocks, the second for all other LEVELs except the
268  * first one in INTRA blocks which is fixed length coded with 8 bits.
269  * NOTE: The two code tables only differ in one VLC so we handle that
270  * manually. */
271  scan_table = s->intra_scantable.permutated;
272  if (s->mb_intra) {
273  /* DC coef */
274  level = get_bits(&s->gb, 8);
275  // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
276  if ((level & 0x7F) == 0) {
277  av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",
278  level, s->mb_x, s->mb_y);
279  return -1;
280  }
281  /* The code 1000 0000 is not used, the reconstruction level of 1024
282  * being coded as 1111 1111. */
283  if (level == 255)
284  level = 128;
285  block[0] = level;
286  i = 1;
287  } else if (coded) {
288  // Run Level Code
289  // EOB Not possible for first level when cbp is available (that's why the table is different)
290  // 0 1 1s
291  // * * 0*
292  int check = show_bits(&s->gb, 2);
293  i = 0;
294  if (check & 0x2) {
295  skip_bits(&s->gb, 2);
296  block[0] = (check & 0x1) ? -1 : 1;
297  i = 1;
298  }
299  } else {
300  i = 0;
301  }
302  if (!coded) {
303  s->block_last_index[n] = i - 1;
304  return 0;
305  }
306  for (;;) {
307  code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
308  if (code < 0) {
309  av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
310  s->mb_x, s->mb_y);
311  return -1;
312  }
313  if (code == rl->n) {
314  /* escape */
315  /* The remaining combinations of (run, level) are encoded with a
316  * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits
317  * level. */
318  run = get_bits(&s->gb, 6);
319  level = get_sbits(&s->gb, 8);
320  } else if (code == 0) {
321  break;
322  } else {
323  run = rl->table_run[code];
324  level = rl->table_level[code];
325  if (get_bits1(&s->gb))
326  level = -level;
327  }
328  i += run;
329  if (i >= 64) {
330  av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",
331  s->mb_x, s->mb_y);
332  return -1;
333  }
334  j = scan_table[i];
335  block[j] = level;
336  i++;
337  }
338  s->block_last_index[n] = i - 1;
339  return 0;
340 }
341 
343 {
344  MpegEncContext *const s = &h->s;
345  int i, cbp, xy;
346 
347  cbp = 63;
348  // Read mba
349  do {
350  h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,
351  H261_MBA_VLC_BITS, 2);
352 
353  /* Check for slice end */
354  /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
355  if (h->mba_diff == MBA_STARTCODE) { // start code
356  h->gob_start_code_skipped = 1;
357  return SLICE_END;
358  }
359  } while (h->mba_diff == MBA_STUFFING); // stuffing
360 
361  if (h->mba_diff < 0) {
362  if (get_bits_left(&s->gb) <= 7)
363  return SLICE_END;
364 
365  av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
366  return SLICE_ERROR;
367  }
368 
369  h->mba_diff += 1;
370  h->current_mba += h->mba_diff;
371 
372  if (h->current_mba > MBA_STUFFING)
373  return SLICE_ERROR;
374 
375  s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);
376  s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);
377  xy = s->mb_x + s->mb_y * s->mb_stride;
380 
381  // Read mtype
382  h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
383  if (h->mtype < 0) {
384  av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",
385  h->mtype);
386  return SLICE_ERROR;
387  }
389  h->mtype = ff_h261_mtype_map[h->mtype];
390 
391  // Read mquant
392  if (IS_QUANT(h->mtype))
393  ff_set_qscale(s, get_bits(&s->gb, 5));
394 
395  s->mb_intra = IS_INTRA4x4(h->mtype);
396 
397  // Read mv
398  if (IS_16X16(h->mtype)) {
399  /* Motion vector data is included for all MC macroblocks. MVD is
400  * obtained from the macroblock vector by subtracting the vector
401  * of the preceding macroblock. For this calculation the vector
402  * of the preceding macroblock is regarded as zero in the
403  * following three situations:
404  * 1) evaluating MVD for macroblocks 1, 12 and 23;
405  * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
406  * 3) MTYPE of the previous macroblock was not MC. */
407  if ((h->current_mba == 1) || (h->current_mba == 12) ||
408  (h->current_mba == 23) || (h->mba_diff != 1)) {
409  h->current_mv_x = 0;
410  h->current_mv_y = 0;
411  }
412 
415  } else {
416  h->current_mv_x = 0;
417  h->current_mv_y = 0;
418  }
419 
420  // Read cbp
421  if (HAS_CBP(h->mtype))
422  cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
423 
424  if (s->mb_intra) {
426  goto intra;
427  }
428 
429  //set motion vectors
430  s->mv_dir = MV_DIR_FORWARD;
431  s->mv_type = MV_TYPE_16X16;
433  s->mv[0][0][0] = h->current_mv_x * 2; // gets divided by 2 in motion compensation
434  s->mv[0][0][1] = h->current_mv_y * 2;
435 
436  if (s->current_picture.motion_val[0]) {
437  int b_stride = 2*s->mb_width + 1;
438  int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
439  s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
440  s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
441  }
442 
443 intra:
444  /* decode each block */
445  if (s->mb_intra || HAS_CBP(h->mtype)) {
446  s->bdsp.clear_blocks(s->block[0]);
447  for (i = 0; i < 6; i++) {
448  if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)
449  return SLICE_ERROR;
450  cbp += cbp;
451  }
452  } else {
453  for (i = 0; i < 6; i++)
454  s->block_last_index[i] = -1;
455  }
456 
457  ff_mpv_decode_mb(s, s->block);
458 
459  return SLICE_OK;
460 }
461 
462 /**
463  * Decode the H.261 picture header.
464  * @return <0 if no startcode found
465  */
467 {
468  MpegEncContext *const s = &h->s;
469  int format, i;
470  uint32_t startcode = 0;
471 
472  for (i = get_bits_left(&s->gb); i > 24; i -= 1) {
473  startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
474 
475  if (startcode == 0x10)
476  break;
477  }
478 
479  if (startcode != 0x10) {
480  av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
481  return -1;
482  }
483 
484  /* temporal reference */
485  i = get_bits(&s->gb, 5); /* picture timestamp */
486  if (i < (s->picture_number & 31))
487  i += 32;
488  s->picture_number = (s->picture_number & ~31) + i;
489 
490  s->avctx->time_base = (AVRational) { 1001, 30000 };
491 
492  /* PTYPE starts here */
493  skip_bits1(&s->gb); /* split screen off */
494  skip_bits1(&s->gb); /* camera off */
495  skip_bits1(&s->gb); /* freeze picture release off */
496 
497  format = get_bits1(&s->gb);
498 
499  // only 2 formats possible
500  if (format == 0) { // QCIF
501  s->width = 176;
502  s->height = 144;
503  s->mb_width = 11;
504  s->mb_height = 9;
505  } else { // CIF
506  s->width = 352;
507  s->height = 288;
508  s->mb_width = 22;
509  s->mb_height = 18;
510  }
511 
512  s->mb_num = s->mb_width * s->mb_height;
513 
514  skip_bits1(&s->gb); /* still image mode off */
515  skip_bits1(&s->gb); /* Reserved */
516 
517  /* PEI */
518  if (skip_1stop_8data_bits(&s->gb) < 0)
519  return AVERROR_INVALIDDATA;
520 
521  /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
522  * frame, the codec crashes if it does not contain all I-blocks
523  * (e.g. when a packet is lost). */
525 
526  h->gob_number = 0;
527  return 0;
528 }
529 
531 {
532  MpegEncContext *const s = &h->s;
533 
534  ff_set_qscale(s, s->qscale);
535 
536  /* decode mb's */
537  while (h->current_mba <= MBA_STUFFING) {
538  int ret;
539  /* DCT & quantize */
540  ret = h261_decode_mb(h);
541  if (ret < 0) {
542  if (ret == SLICE_END) {
544  return 0;
545  }
546  av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",
547  s->mb_x + s->mb_y * s->mb_stride);
548  return -1;
549  }
550 
552  h->current_mba - h->mba_diff,
553  h->current_mba - 1);
554  }
555 
556  return -1;
557 }
558 
559 /**
560  * returns the number of bytes consumed for building the current frame
561  */
562 static int get_consumed_bytes(MpegEncContext *s, int buf_size)
563 {
564  int pos = get_bits_count(&s->gb) >> 3;
565  if (pos == 0)
566  pos = 1; // avoid infinite loops (i doubt that is needed but ...)
567  if (pos + 10 > buf_size)
568  pos = buf_size; // oops ;)
569 
570  return pos;
571 }
572 
573 static int h261_decode_frame(AVCodecContext *avctx, void *data,
574  int *got_frame, AVPacket *avpkt)
575 {
576  const uint8_t *buf = avpkt->data;
577  int buf_size = avpkt->size;
578  H261Context *h = avctx->priv_data;
579  MpegEncContext *s = &h->s;
580  int ret;
581  AVFrame *pict = data;
582 
583  av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
584  av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
585  s->flags = avctx->flags;
586  s->flags2 = avctx->flags2;
587 
588  h->gob_start_code_skipped = 0;
589 
590 retry:
591  init_get_bits(&s->gb, buf, buf_size * 8);
592 
593  if (!s->context_initialized)
594  // we need the IDCT permutaton for reading a custom matrix
595  ff_mpv_idct_init(s);
596 
598 
599  /* skip if the header was thrashed */
600  if (ret < 0) {
601  av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
602  return -1;
603  }
604 
605  if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
606  ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
607  s->parse_context.buffer = 0;
609  s->parse_context = pc;
610  }
611 
612  if (!s->context_initialized) {
613  if ((ret = ff_mpv_common_init(s)) < 0)
614  return ret;
615 
616  ret = ff_set_dimensions(avctx, s->width, s->height);
617  if (ret < 0)
618  return ret;
619 
620  goto retry;
621  }
622 
623  // for skipping the frame
626 
627  if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||
629  avctx->skip_frame >= AVDISCARD_ALL)
630  return get_consumed_bytes(s, buf_size);
631 
632  if (ff_mpv_frame_start(s, avctx) < 0)
633  return -1;
634 
636 
637  /* decode each macroblock */
638  s->mb_x = 0;
639  s->mb_y = 0;
640 
641  while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {
642  if (h261_resync(h) < 0)
643  break;
644  h261_decode_gob(h);
645  }
646  ff_mpv_frame_end(s);
647 
650 
651  if ((ret = av_frame_ref(pict, s->current_picture_ptr->f)) < 0)
652  return ret;
654 
655  *got_frame = 1;
656 
657  return get_consumed_bytes(s, buf_size);
658 }
659 
661 {
662  H261Context *h = avctx->priv_data;
663  MpegEncContext *s = &h->s;
664 
666  return 0;
667 }
668 
670  .name = "h261",
671  .long_name = NULL_IF_CONFIG_SMALL("H.261"),
672  .type = AVMEDIA_TYPE_VIDEO,
673  .id = AV_CODEC_ID_H261,
674  .priv_data_size = sizeof(H261Context),
678  .capabilities = CODEC_CAP_DR1,
679  .max_lowres = 3,
680 };