libavcodec/h261dec.c

   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 h261dec.c
  25  * H.261 decoder.
  26  */
  27
  28 #include "dsputil.h"
  29 #include "avcodec.h"
  30 #include "mpegvideo.h"
  31 #include "h261.h"
  32 #include "h261data.h"
  33
  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
  41
  42 extern uint8_t ff_h261_rl_table_store[2][2*MAX_RUN + MAX_LEVEL + 3];
  43
  44 static VLC h261_mba_vlc;
  45 static VLC h261_mtype_vlc;
  46 static VLC h261_mv_vlc;
  47 static VLC h261_cbp_vlc;
  48
  49 static int h261_decode_block(H261Context * h, DCTELEM * block, int n, int coded);
  50
  51 static void h261_decode_init_vlc(H261Context *h){
  52     static int done = 0;
  53
  54     if(!done){
  55         done = 1;
  56         init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
  57                  h261_mba_bits, 1, 1,
  58                  h261_mba_code, 1, 1, 1);
  59         init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
  60                  h261_mtype_bits, 1, 1,
  61                  h261_mtype_code, 1, 1, 1);
  62         init_vlc(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
  63                  &h261_mv_tab[0][1], 2, 1,
  64                  &h261_mv_tab[0][0], 2, 1, 1);
  65         init_vlc(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
  66                  &h261_cbp_tab[0][1], 2, 1,
  67                  &h261_cbp_tab[0][0], 2, 1, 1);
  68         init_rl(&h261_rl_tcoeff, ff_h261_rl_table_store);
  69         init_vlc_rl(&h261_rl_tcoeff, 1);
  70     }
  71 }
  72
  73 static int h261_decode_init(AVCodecContext *avctx){
  74     H261Context *h= avctx->priv_data;
  75     MpegEncContext * const s = &h->s;
  76
  77     // set defaults
  78     MPV_decode_defaults(s);
  79     s->avctx = avctx;
  80
  81     s->width  = s->avctx->coded_width;
  82     s->height = s->avctx->coded_height;
  83     s->codec_id = s->avctx->codec->id;
  84
  85     s->out_format = FMT_H261;
  86     s->low_delay= 1;
  87     avctx->pix_fmt= PIX_FMT_YUV420P;
  88
  89     s->codec_id= avctx->codec->id;
  90
  91     h261_decode_init_vlc(h);
  92
  93     h->gob_start_code_skipped = 0;
  94
  95     return 0;
  96 }
  97
  98 /**
  99  * decodes the group of blocks header or slice header.
 100  * @return <0 if an error occured
 101  */
 102 static int h261_decode_gob_header(H261Context *h){
 103     unsigned int val;
 104     MpegEncContext * const s = &h->s;
 105
 106     if ( !h->gob_start_code_skipped ){
 107         /* Check for GOB Start Code */
 108         val = show_bits(&s->gb, 15);
 109         if(val)
 110             return -1;
 111
 112         /* We have a GBSC */
 113         skip_bits(&s->gb, 16);
 114     }
 115
 116     h->gob_start_code_skipped = 0;
 117
 118     h->gob_number = get_bits(&s->gb, 4); /* GN */
 119     s->qscale = get_bits(&s->gb, 5); /* GQUANT */
 120
 121     /* Check if gob_number is valid */
 122     if (s->mb_height==18){ //cif
 123         if ((h->gob_number<=0) || (h->gob_number>12))
 124             return -1;
 125     }
 126     else{ //qcif
 127         if ((h->gob_number!=1) && (h->gob_number!=3) && (h->gob_number!=5))
 128             return -1;
 129     }
 130
 131     /* GEI */
 132     while (get_bits1(&s->gb) != 0) {
 133         skip_bits(&s->gb, 8);
 134     }
 135
 136     if(s->qscale==0)
 137         return -1;
 138
 139     // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
 140     // subsequent macroblocks, MBA is the difference between the absolute addresses of
 141     // the macroblock and the last transmitted macroblock.
 142     h->current_mba = 0;
 143     h->mba_diff = 0;
 144
 145     return 0;
 146 }
 147
 148 /**
 149  * decodes the group of blocks / video packet header.
 150  * @return <0 if no resync found
 151  */
 152 static int ff_h261_resync(H261Context *h){
 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     }
 161     else{
 162         if(show_bits(&s->gb, 15)==0){
 163             ret= h261_decode_gob_header(h);
 164             if(ret>=0)
 165                 return 0;
 166         }
 167         //OK, it is not where it is supposed to be ...
 168         s->gb= s->last_resync_gb;
 169         align_get_bits(&s->gb);
 170         left= s->gb.size_in_bits - get_bits_count(&s->gb);
 171
 172         for(;left>15+1+4+5; left-=8){
 173             if(show_bits(&s->gb, 15)==0){
 174                 GetBitContext bak= s->gb;
 175
 176                 ret= h261_decode_gob_header(h);
 177                 if(ret>=0)
 178                     return 0;
 179
 180                 s->gb= bak;
 181             }
 182             skip_bits(&s->gb, 8);
 183         }
 184     }
 185
 186     return -1;
 187 }
 188
 189 /**
 190  * decodes skipped macroblocks
 191  * @return 0
 192  */
 193 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
 194 {
 195     MpegEncContext * const s = &h->s;
 196     int i;
 197
 198     s->mb_intra = 0;
 199
 200     for(i=mba1; i<mba2; i++){
 201         int j, xy;
 202
 203         s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
 204         s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
 205         xy = s->mb_x + s->mb_y * s->mb_stride;
 206         ff_init_block_index(s);
 207         ff_update_block_index(s);
 208
 209         for(j=0;j<6;j++)
 210             s->block_last_index[j] = -1;
 211
 212         s->mv_dir = MV_DIR_FORWARD;
 213         s->mv_type = MV_TYPE_16X16;
 214         s->current_picture.mb_type[xy]= MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
 215         s->mv[0][0][0] = 0;
 216         s->mv[0][0][1] = 0;
 217         s->mb_skipped = 1;
 218         h->mtype &= ~MB_TYPE_H261_FIL;
 219
 220         MPV_decode_mb(s, s->block);
 221     }
 222
 223     return 0;
 224 }
 225
 226 static int decode_mv_component(GetBitContext *gb, int v){
 227     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
 228
 229     /* check if mv_diff is valid */
 230     if ( mv_diff < 0 )
 231         return v;
 232
 233     mv_diff = mvmap[mv_diff];
 234
 235     if(mv_diff && !get_bits1(gb))
 236         mv_diff= -mv_diff;
 237
 238     v += mv_diff;
 239     if     (v <=-16) v+= 32;
 240     else if(v >= 16) v-= 32;
 241
 242     return v;
 243 }
 244
 245 static int h261_decode_mb(H261Context *h){
 246     MpegEncContext * const s = &h->s;
 247     int i, cbp, xy;
 248
 249     cbp = 63;
 250     // Read mba
 251     do{
 252         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);
 253
 254         /* Check for slice end */
 255         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
 256         if (h->mba_diff == MBA_STARTCODE){ // start code
 257             h->gob_start_code_skipped = 1;
 258             return SLICE_END;
 259         }
 260     }
 261     while( h->mba_diff == MBA_STUFFING ); // stuffing
 262
 263     if ( h->mba_diff < 0 ){
 264         if ( get_bits_count(&s->gb) + 7 >= s->gb.size_in_bits )
 265             return SLICE_END;
 266
 267         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
 268         return SLICE_ERROR;
 269     }
 270
 271     h->mba_diff += 1;
 272     h->current_mba += h->mba_diff;
 273
 274     if ( h->current_mba > MBA_STUFFING )
 275         return SLICE_ERROR;
 276
 277     s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
 278     s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
 279     xy = s->mb_x + s->mb_y * s->mb_stride;
 280     ff_init_block_index(s);
 281     ff_update_block_index(s);
 282
 283     // Read mtype
 284     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
 285     h->mtype = h261_mtype_map[h->mtype];
 286
 287     // Read mquant
 288     if ( IS_QUANT ( h->mtype ) ){
 289         ff_set_qscale(s, get_bits(&s->gb, 5));
 290     }
 291
 292     s->mb_intra = IS_INTRA4x4(h->mtype);
 293
 294     // Read mv
 295     if ( IS_16X16 ( h->mtype ) ){
 296         // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
 297         // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
 298         // following three situations:
 299         // 1) evaluating MVD for macroblocks 1, 12 and 23;
 300         // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
 301         // 3) MTYPE of the previous macroblock was not MC.
 302         if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
 303              ( h->mba_diff != 1))
 304         {
 305             h->current_mv_x = 0;
 306             h->current_mv_y = 0;
 307         }
 308
 309         h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
 310         h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
 311     }else{
 312         h->current_mv_x = 0;
 313         h->current_mv_y = 0;
 314     }
 315
 316     // Read cbp
 317     if ( HAS_CBP( h->mtype ) ){
 318         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
 319     }
 320
 321     if(s->mb_intra){
 322         s->current_picture.mb_type[xy]= MB_TYPE_INTRA;
 323         goto intra;
 324     }
 325
 326     //set motion vectors
 327     s->mv_dir = MV_DIR_FORWARD;
 328     s->mv_type = MV_TYPE_16X16;
 329     s->current_picture.mb_type[xy]= MB_TYPE_16x16 | MB_TYPE_L0;
 330     s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
 331     s->mv[0][0][1] = h->current_mv_y * 2;
 332
 333 intra:
 334     /* decode each block */
 335     if(s->mb_intra || HAS_CBP(h->mtype)){
 336         s->dsp.clear_blocks(s->block[0]);
 337         for (i = 0; i < 6; i++) {
 338             if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
 339                 return SLICE_ERROR;
 340             }
 341             cbp+=cbp;
 342         }
 343     }else{
 344         for (i = 0; i < 6; i++)
 345             s->block_last_index[i]= -1;
 346     }
 347
 348     MPV_decode_mb(s, s->block);
 349
 350     return SLICE_OK;
 351 }
 352
 353 /**
 354  * decodes a macroblock
 355  * @return <0 if an error occured
 356  */
 357 static int h261_decode_block(H261Context * h, DCTELEM * block,
 358                              int n, int coded)
 359 {
 360     MpegEncContext * const s = &h->s;
 361     int code, level, i, j, run;
 362     RLTable *rl = &h261_rl_tcoeff;
 363     const uint8_t *scan_table;
 364
 365     // For the variable length encoding there are two code tables, one being used for
 366     // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
 367     // for all other LEVELs except the first one in INTRA blocks which is fixed length
 368     // coded with 8 bits.
 369     // NOTE: the two code tables only differ in one VLC so we handle that manually.
 370     scan_table = s->intra_scantable.permutated;
 371     if (s->mb_intra){
 372         /* DC coef */
 373         level = get_bits(&s->gb, 8);
 374         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
 375         if((level&0x7F) == 0){
 376             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
 377             return -1;
 378         }
 379         // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
 380         if (level == 255)
 381             level = 128;
 382         block[0] = level;
 383         i = 1;
 384     }else if(coded){
 385         // Run  Level   Code
 386         // EOB                  Not possible for first level when cbp is available (that's why the table is different)
 387         // 0    1               1s
 388         // *    *               0*
 389         int check = show_bits(&s->gb, 2);
 390         i = 0;
 391         if ( check & 0x2 ){
 392             skip_bits(&s->gb, 2);
 393             block[0] = ( check & 0x1 ) ? -1 : 1;
 394             i = 1;
 395         }
 396     }else{
 397         i = 0;
 398     }
 399     if(!coded){
 400         s->block_last_index[n] = i - 1;
 401         return 0;
 402     }
 403     for(;;){
 404         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
 405         if (code < 0){
 406             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
 407             return -1;
 408         }
 409         if (code == rl->n) {
 410             /* escape */
 411             // The remaining combinations of (run, level) are encoded with a 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits level.
 412             run = get_bits(&s->gb, 6);
 413             level = get_sbits(&s->gb, 8);
 414         }else if(code == 0){
 415             break;
 416         }else{
 417             run = rl->table_run[code];
 418             level = rl->table_level[code];
 419             if (get_bits1(&s->gb))
 420                 level = -level;
 421         }
 422         i += run;
 423         if (i >= 64){
 424             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
 425             return -1;
 426         }
 427         j = scan_table[i];
 428         block[j] = level;
 429         i++;
 430     }
 431     s->block_last_index[n] = i-1;
 432     return 0;
 433 }
 434
 435 /**
 436  * decodes the H261 picture header.
 437  * @return <0 if no startcode found
 438  */
 439 static int h261_decode_picture_header(H261Context *h){
 440     MpegEncContext * const s = &h->s;
 441     int format, i;
 442     uint32_t startcode= 0;
 443
 444     for(i= s->gb.size_in_bits - get_bits_count(&s->gb); i>24; i-=1){
 445         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
 446
 447         if(startcode == 0x10)
 448             break;
 449     }
 450
 451     if (startcode != 0x10){
 452         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
 453         return -1;
 454     }
 455
 456     /* temporal reference */
 457     i= get_bits(&s->gb, 5); /* picture timestamp */
 458     if(i < (s->picture_number&31))
 459         i += 32;
 460     s->picture_number = (s->picture_number&~31) + i;
 461
 462     s->avctx->time_base= (AVRational){1001, 30000};
 463     s->current_picture.pts= s->picture_number;
 464
 465
 466     /* PTYPE starts here */
 467     skip_bits1(&s->gb); /* split screen off */
 468     skip_bits1(&s->gb); /* camera  off */
 469     skip_bits1(&s->gb); /* freeze picture release off */
 470
 471     format = get_bits1(&s->gb);
 472
 473     //only 2 formats possible
 474     if (format == 0){//QCIF
 475         s->width = 176;
 476         s->height = 144;
 477         s->mb_width = 11;
 478         s->mb_height = 9;
 479     }else{//CIF
 480         s->width = 352;
 481         s->height = 288;
 482         s->mb_width = 22;
 483         s->mb_height = 18;
 484     }
 485
 486     s->mb_num = s->mb_width * s->mb_height;
 487
 488     skip_bits1(&s->gb); /* still image mode off */
 489     skip_bits1(&s->gb); /* Reserved */
 490
 491     /* PEI */
 492     while (get_bits1(&s->gb) != 0){
 493         skip_bits(&s->gb, 8);
 494     }
 495
 496     // h261 has no I-FRAMES, but if we pass I_TYPE for the first frame, the codec crashes if it does
 497     // not contain all I-blocks (e.g. when a packet is lost)
 498     s->pict_type = P_TYPE;
 499
 500     h->gob_number = 0;
 501     return 0;
 502 }
 503
 504 static int h261_decode_gob(H261Context *h){
 505     MpegEncContext * const s = &h->s;
 506
 507     ff_set_qscale(s, s->qscale);
 508
 509     /* decode mb's */
 510     while(h->current_mba <= MBA_STUFFING)
 511     {
 512         int ret;
 513         /* DCT & quantize */
 514         ret= h261_decode_mb(h);
 515         if(ret<0){
 516             if(ret==SLICE_END){
 517                 h261_decode_mb_skipped(h, h->current_mba, 33);
 518                 return 0;
 519             }
 520             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
 521             return -1;
 522         }
 523
 524         h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
 525     }
 526
 527     return -1;
 528 }
 529
 530 /**
 531  * returns the number of bytes consumed for building the current frame
 532  */
 533 static int get_consumed_bytes(MpegEncContext *s, int buf_size){
 534     int pos= get_bits_count(&s->gb)>>3;
 535     if(pos==0) pos=1; //avoid infinite loops (i doubt that is needed but ...)
 536     if(pos+10>buf_size) pos=buf_size; // oops ;)
 537
 538     return pos;
 539 }
 540
 541 static int h261_decode_frame(AVCodecContext *avctx,
 542                              void *data, int *data_size,
 543                              uint8_t *buf, int buf_size)
 544 {
 545     H261Context *h= avctx->priv_data;
 546     MpegEncContext *s = &h->s;
 547     int ret;
 548     AVFrame *pict = data;
 549
 550 #ifdef DEBUG
 551     av_log(avctx, AV_LOG_DEBUG, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
 552     av_log(avctx, AV_LOG_DEBUG, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
 553 #endif
 554     s->flags= avctx->flags;
 555     s->flags2= avctx->flags2;
 556
 557     h->gob_start_code_skipped=0;
 558
 559 retry:
 560
 561     init_get_bits(&s->gb, buf, buf_size*8);
 562
 563     if(!s->context_initialized){
 564         if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
 565             return -1;
 566     }
 567
 568     //we need to set current_picture_ptr before reading the header, otherwise we cannot store anyting im there
 569     if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
 570         int i= ff_find_unused_picture(s, 0);
 571         s->current_picture_ptr= &s->picture[i];
 572     }
 573
 574     ret = h261_decode_picture_header(h);
 575
 576     /* skip if the header was thrashed */
 577     if (ret < 0){
 578         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
 579         return -1;
 580     }
 581
 582     if (s->width != avctx->coded_width || s->height != avctx->coded_height){
 583         ParseContext pc= s->parse_context; //FIXME move this demuxing hack to libavformat
 584         s->parse_context.buffer=0;
 585         MPV_common_end(s);
 586         s->parse_context= pc;
 587     }
 588     if (!s->context_initialized) {
 589         avcodec_set_dimensions(avctx, s->width, s->height);
 590
 591         goto retry;
 592     }
 593
 594     // for hurry_up==5
 595     s->current_picture.pict_type= s->pict_type;
 596     s->current_picture.key_frame= s->pict_type == I_TYPE;
 597
 598     /* skip everything if we are in a hurry>=5 */
 599     if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);
 600     if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==B_TYPE)
 601        ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=I_TYPE)
 602        || avctx->skip_frame >= AVDISCARD_ALL)
 603         return get_consumed_bytes(s, buf_size);
 604
 605     if(MPV_frame_start(s, avctx) < 0)
 606         return -1;
 607
 608     ff_er_frame_start(s);
 609
 610     /* decode each macroblock */
 611     s->mb_x=0;
 612     s->mb_y=0;
 613
 614     while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
 615         if(ff_h261_resync(h)<0)
 616             break;
 617         h261_decode_gob(h);
 618     }
 619     MPV_frame_end(s);
 620
 621 assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
 622 assert(s->current_picture.pict_type == s->pict_type);
 623     *pict= *(AVFrame*)s->current_picture_ptr;
 624     ff_print_debug_info(s, pict);
 625
 626     *data_size = sizeof(AVFrame);
 627
 628     return get_consumed_bytes(s, buf_size);
 629 }
 630
 631 static int h261_decode_end(AVCodecContext *avctx)
 632 {
 633     H261Context *h= avctx->priv_data;
 634     MpegEncContext *s = &h->s;
 635
 636     MPV_common_end(s);
 637     return 0;
 638 }
 639
 640 AVCodec h261_decoder = {
 641     "h261",
 642     CODEC_TYPE_VIDEO,
 643     CODEC_ID_H261,
 644     sizeof(H261Context),
 645     h261_decode_init,
 646     NULL,
 647     h261_decode_end,
 648     h261_decode_frame,
 649     CODEC_CAP_DR1,
 650 };