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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  ff_mpv_decode_init(s, avctx);
80 
81  s->out_format = FMT_H261;
82  s->low_delay = 1;
83  avctx->pix_fmt = AV_PIX_FMT_YUV420P;
84 
87 
89 
90  return 0;
91 }
92 
93 /**
94  * Decode the group of blocks header or slice header.
95  * @return <0 if an error occurred
96  */
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  if (skip_1stop_8data_bits(&s->gb) < 0)
129  return AVERROR_INVALIDDATA;
130 
131  if (s->qscale == 0) {
132  av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
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;
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;
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 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  {
304  OPEN_READER(re, &s->gb);
305  i--; // offset by -1 to allow direct indexing of scan_table
306  for (;;) {
307  UPDATE_CACHE(re, &s->gb);
308  GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TCOEFF_VLC_BITS, 2, 0);
309  if (run == 66) {
310  if (level) {
311  CLOSE_READER(re, &s->gb);
312  av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
313  s->mb_x, s->mb_y);
314  return -1;
315  }
316  /* escape */
317  /* The remaining combinations of (run, level) are encoded with a
318  * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits
319  * level. */
320  run = SHOW_UBITS(re, &s->gb, 6) + 1;
321  SKIP_CACHE(re, &s->gb, 6);
322  level = SHOW_SBITS(re, &s->gb, 8);
323  SKIP_COUNTER(re, &s->gb, 6 + 8);
324  } else if (level == 0) {
325  break;
326  } else {
327  if (SHOW_UBITS(re, &s->gb, 1))
328  level = -level;
329  SKIP_COUNTER(re, &s->gb, 1);
330  }
331  i += run;
332  if (i >= 64) {
333  CLOSE_READER(re, &s->gb);
334  av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",
335  s->mb_x, s->mb_y);
336  return -1;
337  }
338  j = scan_table[i];
339  block[j] = level;
340  }
341  CLOSE_READER(re, &s->gb);
342  }
343  s->block_last_index[n] = i;
344  return 0;
345 }
346 
348 {
349  MpegEncContext *const s = &h->s;
350  int i, cbp, xy;
351 
352  cbp = 63;
353  // Read mba
354  do {
355  h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,
356  H261_MBA_VLC_BITS, 2);
357 
358  /* Check for slice end */
359  /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
360  if (h->mba_diff == MBA_STARTCODE) { // start code
361  h->gob_start_code_skipped = 1;
362  return SLICE_END;
363  }
364  } while (h->mba_diff == MBA_STUFFING); // stuffing
365 
366  if (h->mba_diff < 0) {
367  if (get_bits_left(&s->gb) <= 7)
368  return SLICE_END;
369 
370  av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
371  return SLICE_ERROR;
372  }
373 
374  h->mba_diff += 1;
375  h->current_mba += h->mba_diff;
376 
377  if (h->current_mba > MBA_STUFFING)
378  return SLICE_ERROR;
379 
380  s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);
381  s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);
382  xy = s->mb_x + s->mb_y * s->mb_stride;
385 
386  // Read mtype
387  h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
388  if (h->mtype < 0) {
389  av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",
390  h->mtype);
391  return SLICE_ERROR;
392  }
394  h->mtype = ff_h261_mtype_map[h->mtype];
395 
396  // Read mquant
397  if (IS_QUANT(h->mtype))
398  ff_set_qscale(s, get_bits(&s->gb, 5));
399 
400  s->mb_intra = IS_INTRA4x4(h->mtype);
401 
402  // Read mv
403  if (IS_16X16(h->mtype)) {
404  /* Motion vector data is included for all MC macroblocks. MVD is
405  * obtained from the macroblock vector by subtracting the vector
406  * of the preceding macroblock. For this calculation the vector
407  * of the preceding macroblock is regarded as zero in the
408  * following three situations:
409  * 1) evaluating MVD for macroblocks 1, 12 and 23;
410  * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
411  * 3) MTYPE of the previous macroblock was not MC. */
412  if ((h->current_mba == 1) || (h->current_mba == 12) ||
413  (h->current_mba == 23) || (h->mba_diff != 1)) {
414  h->current_mv_x = 0;
415  h->current_mv_y = 0;
416  }
417 
420  } else {
421  h->current_mv_x = 0;
422  h->current_mv_y = 0;
423  }
424 
425  // Read cbp
426  if (HAS_CBP(h->mtype))
427  cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
428 
429  if (s->mb_intra) {
431  goto intra;
432  }
433 
434  //set motion vectors
435  s->mv_dir = MV_DIR_FORWARD;
436  s->mv_type = MV_TYPE_16X16;
438  s->mv[0][0][0] = h->current_mv_x * 2; // gets divided by 2 in motion compensation
439  s->mv[0][0][1] = h->current_mv_y * 2;
440 
441  if (s->current_picture.motion_val[0]) {
442  int b_stride = 2*s->mb_width + 1;
443  int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
444  s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
445  s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
446  }
447 
448 intra:
449  /* decode each block */
450  if (s->mb_intra || HAS_CBP(h->mtype)) {
451  s->bdsp.clear_blocks(s->block[0]);
452  for (i = 0; i < 6; i++) {
453  if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)
454  return SLICE_ERROR;
455  cbp += cbp;
456  }
457  } else {
458  for (i = 0; i < 6; i++)
459  s->block_last_index[i] = -1;
460  }
461 
462  ff_mpv_decode_mb(s, s->block);
463 
464  return SLICE_OK;
465 }
466 
467 /**
468  * Decode the H.261 picture header.
469  * @return <0 if no startcode found
470  */
472 {
473  MpegEncContext *const s = &h->s;
474  int format, i;
475  uint32_t startcode = 0;
476 
477  for (i = get_bits_left(&s->gb); i > 24; i -= 1) {
478  startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
479 
480  if (startcode == 0x10)
481  break;
482  }
483 
484  if (startcode != 0x10) {
485  av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
486  return -1;
487  }
488 
489  /* temporal reference */
490  i = get_bits(&s->gb, 5); /* picture timestamp */
491  if (i < (s->picture_number & 31))
492  i += 32;
493  s->picture_number = (s->picture_number & ~31) + i;
494 
495  s->avctx->framerate = (AVRational) { 30000, 1001 };
496 
497  /* PTYPE starts here */
498  skip_bits1(&s->gb); /* split screen off */
499  skip_bits1(&s->gb); /* camera off */
500  skip_bits1(&s->gb); /* freeze picture release off */
501 
502  format = get_bits1(&s->gb);
503 
504  // only 2 formats possible
505  if (format == 0) { // QCIF
506  s->width = 176;
507  s->height = 144;
508  s->mb_width = 11;
509  s->mb_height = 9;
510  } else { // CIF
511  s->width = 352;
512  s->height = 288;
513  s->mb_width = 22;
514  s->mb_height = 18;
515  }
516 
517  s->mb_num = s->mb_width * s->mb_height;
518 
519  skip_bits1(&s->gb); /* still image mode off */
520  skip_bits1(&s->gb); /* Reserved */
521 
522  /* PEI */
523  if (skip_1stop_8data_bits(&s->gb) < 0)
524  return AVERROR_INVALIDDATA;
525 
526  /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
527  * frame, the codec crashes if it does not contain all I-blocks
528  * (e.g. when a packet is lost). */
530 
531  h->gob_number = 0;
532  return 0;
533 }
534 
536 {
537  MpegEncContext *const s = &h->s;
538 
539  ff_set_qscale(s, s->qscale);
540 
541  /* decode mb's */
542  while (h->current_mba <= MBA_STUFFING) {
543  int ret;
544  /* DCT & quantize */
545  ret = h261_decode_mb(h);
546  if (ret < 0) {
547  if (ret == SLICE_END) {
549  return 0;
550  }
551  av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",
552  s->mb_x + s->mb_y * s->mb_stride);
553  return -1;
554  }
555 
557  h->current_mba - h->mba_diff,
558  h->current_mba - 1);
559  }
560 
561  return -1;
562 }
563 
564 /**
565  * returns the number of bytes consumed for building the current frame
566  */
567 static int get_consumed_bytes(MpegEncContext *s, int buf_size)
568 {
569  int pos = get_bits_count(&s->gb) >> 3;
570  if (pos == 0)
571  pos = 1; // avoid infinite loops (i doubt that is needed but ...)
572  if (pos + 10 > buf_size)
573  pos = buf_size; // oops ;)
574 
575  return pos;
576 }
577 
578 static int h261_decode_frame(AVCodecContext *avctx, void *data,
579  int *got_frame, AVPacket *avpkt)
580 {
581  const uint8_t *buf = avpkt->data;
582  int buf_size = avpkt->size;
583  H261Context *h = avctx->priv_data;
584  MpegEncContext *s = &h->s;
585  int ret;
586  AVFrame *pict = data;
587 
588  av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
589  av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
590  s->flags = avctx->flags;
591  s->flags2 = avctx->flags2;
592 
593  h->gob_start_code_skipped = 0;
594 
595 retry:
596  init_get_bits(&s->gb, buf, buf_size * 8);
597 
598  if (!s->context_initialized)
599  // we need the IDCT permutaton for reading a custom matrix
600  ff_mpv_idct_init(s);
601 
603 
604  /* skip if the header was thrashed */
605  if (ret < 0) {
606  av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
607  return -1;
608  }
609 
610  if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
611  ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
612  s->parse_context.buffer = 0;
614  s->parse_context = pc;
615  }
616 
617  if (!s->context_initialized) {
618  if ((ret = ff_mpv_common_init(s)) < 0)
619  return ret;
620 
621  ret = ff_set_dimensions(avctx, s->width, s->height);
622  if (ret < 0)
623  return ret;
624 
625  goto retry;
626  }
627 
628  // for skipping the frame
631 
632  if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||
634  avctx->skip_frame >= AVDISCARD_ALL)
635  return get_consumed_bytes(s, buf_size);
636 
637  if (ff_mpv_frame_start(s, avctx) < 0)
638  return -1;
639 
641 
642  /* decode each macroblock */
643  s->mb_x = 0;
644  s->mb_y = 0;
645 
646  while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {
647  if (h261_resync(h) < 0)
648  break;
649  h261_decode_gob(h);
650  }
651  ff_mpv_frame_end(s);
652 
655 
656  if ((ret = av_frame_ref(pict, s->current_picture_ptr->f)) < 0)
657  return ret;
659 
660  *got_frame = 1;
661 
662  return get_consumed_bytes(s, buf_size);
663 }
664 
666 {
667  H261Context *h = avctx->priv_data;
668  MpegEncContext *s = &h->s;
669 
671  return 0;
672 }
673 
675  .name = "h261",
676  .long_name = NULL_IF_CONFIG_SMALL("H.261"),
677  .type = AVMEDIA_TYPE_VIDEO,
678  .id = AV_CODEC_ID_H261,
679  .priv_data_size = sizeof(H261Context),
681  .close = h261_decode_end,
683  .capabilities = CODEC_CAP_DR1,
684  .max_lowres = 3,
685 };