libavcodec/h261.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 h261.c
  25  * h261codec.
  26  */
  27
  28 #include "dsputil.h"
  29 #include "avcodec.h"
  30 #include "mpegvideo.h"
  31 #include "h261data.h"
  32
  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
  40 #define MBA_STUFFING 33
  41 #define MBA_STARTCODE 34
  42 #define IS_FIL(a)    ((a)&MB_TYPE_H261_FIL)
  43
  44 /**
  45  * H261Context
  46  */
  47 typedef struct H261Context{
  48     MpegEncContext s;
  49
  50     int current_mba;
  51     int previous_mba;
  52     int mba_diff;
  53     int mtype;
  54     int current_mv_x;
  55     int current_mv_y;
  56     int gob_number;
  57     int gob_start_code_skipped; // 1 if gob start code is already read before gob header is read
  58 }H261Context;
  59
  60 static uint8_t static_rl_table_store[2][2*MAX_RUN + MAX_LEVEL + 3];
  61
  62 void ff_h261_loop_filter(MpegEncContext *s){
  63     H261Context * h= (H261Context*)s;
  64     const int linesize  = s->linesize;
  65     const int uvlinesize= s->uvlinesize;
  66     uint8_t *dest_y = s->dest[0];
  67     uint8_t *dest_cb= s->dest[1];
  68     uint8_t *dest_cr= s->dest[2];
  69
  70     if(!(IS_FIL (h->mtype)))
  71         return;
  72
  73     s->dsp.h261_loop_filter(dest_y                   , linesize);
  74     s->dsp.h261_loop_filter(dest_y                + 8, linesize);
  75     s->dsp.h261_loop_filter(dest_y + 8 * linesize    , linesize);
  76     s->dsp.h261_loop_filter(dest_y + 8 * linesize + 8, linesize);
  77     s->dsp.h261_loop_filter(dest_cb, uvlinesize);
  78     s->dsp.h261_loop_filter(dest_cr, uvlinesize);
  79 }
  80
  81 int ff_h261_get_picture_format(int width, int height){
  82     // QCIF
  83     if (width == 176 && height == 144)
  84         return 0;
  85     // CIF
  86     else if (width == 352 && height == 288)
  87         return 1;
  88     // ERROR
  89     else
  90         return -1;
  91 }
  92
  93 static void h261_encode_block(H261Context * h, DCTELEM * block,
  94                               int n);
  95 static int h261_decode_block(H261Context *h, DCTELEM *block,
  96                              int n, int coded);
  97
  98 void ff_h261_encode_picture_header(MpegEncContext * s, int picture_number){
  99     H261Context * h = (H261Context *) s;
 100     int format, temp_ref;
 101
 102     align_put_bits(&s->pb);
 103
 104     /* Update the pointer to last GOB */
 105     s->ptr_lastgob = pbBufPtr(&s->pb);
 106
 107     put_bits(&s->pb, 20, 0x10); /* PSC */
 108
 109     temp_ref= s->picture_number * (int64_t)30000 * s->avctx->time_base.num /
 110                          (1001 * (int64_t)s->avctx->time_base.den); //FIXME maybe this should use a timestamp
 111     put_bits(&s->pb, 5, temp_ref & 0x1f); /* TemporalReference */
 112
 113     put_bits(&s->pb, 1, 0); /* split screen off */
 114     put_bits(&s->pb, 1, 0); /* camera  off */
 115     put_bits(&s->pb, 1, 0); /* freeze picture release off */
 116
 117     format = ff_h261_get_picture_format(s->width, s->height);
 118
 119     put_bits(&s->pb, 1, format); /* 0 == QCIF, 1 == CIF */
 120
 121     put_bits(&s->pb, 1, 0); /* still image mode */
 122     put_bits(&s->pb, 1, 0); /* reserved */
 123
 124     put_bits(&s->pb, 1, 0); /* no PEI */
 125     if(format == 0)
 126         h->gob_number = -1;
 127     else
 128         h->gob_number = 0;
 129     h->current_mba = 0;
 130 }
 131
 132 /**
 133  * Encodes a group of blocks header.
 134  */
 135 static void h261_encode_gob_header(MpegEncContext * s, int mb_line){
 136     H261Context * h = (H261Context *)s;
 137     if(ff_h261_get_picture_format(s->width, s->height) == 0){
 138         h->gob_number+=2; // QCIF
 139     }
 140     else{
 141         h->gob_number++; // CIF
 142     }
 143     put_bits(&s->pb, 16, 1); /* GBSC */
 144     put_bits(&s->pb, 4, h->gob_number); /* GN */
 145     put_bits(&s->pb, 5, s->qscale); /* GQUANT */
 146     put_bits(&s->pb, 1, 0); /* no GEI */
 147     h->current_mba = 0;
 148     h->previous_mba = 0;
 149     h->current_mv_x=0;
 150     h->current_mv_y=0;
 151 }
 152
 153 void ff_h261_reorder_mb_index(MpegEncContext* s){
 154     int index= s->mb_x + s->mb_y*s->mb_width;
 155
 156     if(index % 33 == 0)
 157         h261_encode_gob_header(s,0);
 158
 159     /* for CIF the GOB's are fragmented in the middle of a scanline
 160        that's why we need to adjust the x and y index of the macroblocks */
 161     if(ff_h261_get_picture_format(s->width,s->height) == 1){ // CIF
 162         s->mb_x =     index % 11 ; index /= 11;
 163         s->mb_y =     index %  3 ; index /=  3;
 164         s->mb_x+= 11*(index %  2); index /=  2;
 165         s->mb_y+=  3*index;
 166
 167         ff_init_block_index(s);
 168         ff_update_block_index(s);
 169     }
 170 }
 171
 172 static void h261_encode_motion(H261Context * h, int val){
 173     MpegEncContext * const s = &h->s;
 174     int sign, code;
 175     if(val==0){
 176         code = 0;
 177         put_bits(&s->pb,h261_mv_tab[code][1],h261_mv_tab[code][0]);
 178     }
 179     else{
 180         if(val > 15)
 181             val -=32;
 182         if(val < -16)
 183             val+=32;
 184         sign = val < 0;
 185         code = sign ? -val : val;
 186         put_bits(&s->pb,h261_mv_tab[code][1],h261_mv_tab[code][0]);
 187         put_bits(&s->pb,1,sign);
 188     }
 189 }
 190
 191 static inline int get_cbp(MpegEncContext * s,
 192                       DCTELEM block[6][64])
 193 {
 194     int i, cbp;
 195     cbp= 0;
 196     for (i = 0; i < 6; i++) {
 197         if (s->block_last_index[i] >= 0)
 198             cbp |= 1 << (5 - i);
 199     }
 200     return cbp;
 201 }
 202 void ff_h261_encode_mb(MpegEncContext * s,
 203          DCTELEM block[6][64],
 204          int motion_x, int motion_y)
 205 {
 206     H261Context * h = (H261Context *)s;
 207     int mvd, mv_diff_x, mv_diff_y, i, cbp;
 208     cbp = 63; // avoid warning
 209     mvd = 0;
 210
 211     h->current_mba++;
 212     h->mtype = 0;
 213
 214     if (!s->mb_intra){
 215         /* compute cbp */
 216         cbp= get_cbp(s, block);
 217
 218         /* mvd indicates if this block is motion compensated */
 219         mvd = motion_x | motion_y;
 220
 221         if((cbp | mvd | s->dquant ) == 0) {
 222             /* skip macroblock */
 223             s->skip_count++;
 224             h->current_mv_x=0;
 225             h->current_mv_y=0;
 226             return;
 227         }
 228     }
 229
 230     /* MB is not skipped, encode MBA */
 231     put_bits(&s->pb, h261_mba_bits[(h->current_mba-h->previous_mba)-1], h261_mba_code[(h->current_mba-h->previous_mba)-1]);
 232
 233     /* calculate MTYPE */
 234     if(!s->mb_intra){
 235         h->mtype++;
 236
 237         if(mvd || s->loop_filter)
 238             h->mtype+=3;
 239         if(s->loop_filter)
 240             h->mtype+=3;
 241         if(cbp || s->dquant)
 242             h->mtype++;
 243         assert(h->mtype > 1);
 244     }
 245
 246     if(s->dquant)
 247         h->mtype++;
 248
 249     put_bits(&s->pb, h261_mtype_bits[h->mtype], h261_mtype_code[h->mtype]);
 250
 251     h->mtype = h261_mtype_map[h->mtype];
 252
 253     if(IS_QUANT(h->mtype)){
 254         ff_set_qscale(s,s->qscale+s->dquant);
 255         put_bits(&s->pb, 5, s->qscale);
 256     }
 257
 258     if(IS_16X16(h->mtype)){
 259         mv_diff_x = (motion_x >> 1) - h->current_mv_x;
 260         mv_diff_y = (motion_y >> 1) - h->current_mv_y;
 261         h->current_mv_x = (motion_x >> 1);
 262         h->current_mv_y = (motion_y >> 1);
 263         h261_encode_motion(h,mv_diff_x);
 264         h261_encode_motion(h,mv_diff_y);
 265     }
 266
 267     h->previous_mba = h->current_mba;
 268
 269     if(HAS_CBP(h->mtype)){
 270         assert(cbp>0);
 271         put_bits(&s->pb,h261_cbp_tab[cbp-1][1],h261_cbp_tab[cbp-1][0]);
 272     }
 273     for(i=0; i<6; i++) {
 274         /* encode each block */
 275         h261_encode_block(h, block[i], i);
 276     }
 277
 278     if ( ( h->current_mba == 11 ) || ( h->current_mba == 22 ) || ( h->current_mba == 33 ) || ( !IS_16X16 ( h->mtype ) )){
 279         h->current_mv_x=0;
 280         h->current_mv_y=0;
 281     }
 282 }
 283
 284 void ff_h261_encode_init(MpegEncContext *s){
 285     static int done = 0;
 286
 287     if (!done) {
 288         done = 1;
 289         init_rl(&h261_rl_tcoeff, static_rl_table_store);
 290     }
 291
 292     s->min_qcoeff= -127;
 293     s->max_qcoeff=  127;
 294     s->y_dc_scale_table=
 295     s->c_dc_scale_table= ff_mpeg1_dc_scale_table;
 296 }
 297
 298
 299 /**
 300  * encodes a 8x8 block.
 301  * @param block the 8x8 block
 302  * @param n block index (0-3 are luma, 4-5 are chroma)
 303  */
 304 static void h261_encode_block(H261Context * h, DCTELEM * block, int n){
 305     MpegEncContext * const s = &h->s;
 306     int level, run, last, i, j, last_index, last_non_zero, sign, slevel, code;
 307     RLTable *rl;
 308
 309     rl = &h261_rl_tcoeff;
 310     if (s->mb_intra) {
 311         /* DC coef */
 312         level = block[0];
 313         /* 255 cannot be represented, so we clamp */
 314         if (level > 254) {
 315             level = 254;
 316             block[0] = 254;
 317         }
 318         /* 0 cannot be represented also */
 319         else if (level < 1) {
 320             level = 1;
 321             block[0] = 1;
 322         }
 323         if (level == 128)
 324             put_bits(&s->pb, 8, 0xff);
 325         else
 326             put_bits(&s->pb, 8, level);
 327         i = 1;
 328     } else if((block[0]==1 || block[0] == -1) && (s->block_last_index[n] > -1)){
 329         //special case
 330         put_bits(&s->pb,2,block[0]>0 ? 2 : 3 );
 331         i = 1;
 332     } else {
 333         i = 0;
 334     }
 335
 336     /* AC coefs */
 337     last_index = s->block_last_index[n];
 338     last_non_zero = i - 1;
 339     for (; i <= last_index; i++) {
 340         j = s->intra_scantable.permutated[i];
 341         level = block[j];
 342         if (level) {
 343             run = i - last_non_zero - 1;
 344             last = (i == last_index);
 345             sign = 0;
 346             slevel = level;
 347             if (level < 0) {
 348                 sign = 1;
 349                 level = -level;
 350             }
 351             code = get_rl_index(rl, 0 /*no last in H.261, EOB is used*/, run, level);
 352             if(run==0 && level < 16)
 353             code+=1;
 354             put_bits(&s->pb, rl->table_vlc[code][1], rl->table_vlc[code][0]);
 355             if (code == rl->n) {
 356                 put_bits(&s->pb, 6, run);
 357                 assert(slevel != 0);
 358                 assert(level <= 127);
 359                 put_bits(&s->pb, 8, slevel & 0xff);
 360             } else {
 361                 put_bits(&s->pb, 1, sign);
 362             }
 363             last_non_zero = i;
 364         }
 365     }
 366     if(last_index > -1){
 367         put_bits(&s->pb, rl->table_vlc[0][1], rl->table_vlc[0][0]);// END OF BLOCK
 368     }
 369 }
 370
 371 /***********************************************/
 372 /* decoding */
 373
 374 static VLC h261_mba_vlc;
 375 static VLC h261_mtype_vlc;
 376 static VLC h261_mv_vlc;
 377 static VLC h261_cbp_vlc;
 378
 379 static void h261_decode_init_vlc(H261Context *h){
 380     static int done = 0;
 381
 382     if(!done){
 383         done = 1;
 384         init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
 385                  h261_mba_bits, 1, 1,
 386                  h261_mba_code, 1, 1, 1);
 387         init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
 388                  h261_mtype_bits, 1, 1,
 389                  h261_mtype_code, 1, 1, 1);
 390         init_vlc(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
 391                  &h261_mv_tab[0][1], 2, 1,
 392                  &h261_mv_tab[0][0], 2, 1, 1);
 393         init_vlc(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
 394                  &h261_cbp_tab[0][1], 2, 1,
 395                  &h261_cbp_tab[0][0], 2, 1, 1);
 396         init_rl(&h261_rl_tcoeff, static_rl_table_store);
 397         init_vlc_rl(&h261_rl_tcoeff, 1);
 398     }
 399 }
 400
 401 static int h261_decode_init(AVCodecContext *avctx){
 402     H261Context *h= avctx->priv_data;
 403     MpegEncContext * const s = &h->s;
 404
 405     // set defaults
 406     MPV_decode_defaults(s);
 407     s->avctx = avctx;
 408
 409     s->width  = s->avctx->coded_width;
 410     s->height = s->avctx->coded_height;
 411     s->codec_id = s->avctx->codec->id;
 412
 413     s->out_format = FMT_H261;
 414     s->low_delay= 1;
 415     avctx->pix_fmt= PIX_FMT_YUV420P;
 416
 417     s->codec_id= avctx->codec->id;
 418
 419     h261_decode_init_vlc(h);
 420
 421     h->gob_start_code_skipped = 0;
 422
 423     return 0;
 424 }
 425
 426 /**
 427  * decodes the group of blocks header or slice header.
 428  * @return <0 if an error occured
 429  */
 430 static int h261_decode_gob_header(H261Context *h){
 431     unsigned int val;
 432     MpegEncContext * const s = &h->s;
 433
 434     if ( !h->gob_start_code_skipped ){
 435         /* Check for GOB Start Code */
 436         val = show_bits(&s->gb, 15);
 437         if(val)
 438             return -1;
 439
 440         /* We have a GBSC */
 441         skip_bits(&s->gb, 16);
 442     }
 443
 444     h->gob_start_code_skipped = 0;
 445
 446     h->gob_number = get_bits(&s->gb, 4); /* GN */
 447     s->qscale = get_bits(&s->gb, 5); /* GQUANT */
 448
 449     /* Check if gob_number is valid */
 450     if (s->mb_height==18){ //cif
 451         if ((h->gob_number<=0) || (h->gob_number>12))
 452             return -1;
 453     }
 454     else{ //qcif
 455         if ((h->gob_number!=1) && (h->gob_number!=3) && (h->gob_number!=5))
 456             return -1;
 457     }
 458
 459     /* GEI */
 460     while (get_bits1(&s->gb) != 0) {
 461         skip_bits(&s->gb, 8);
 462     }
 463
 464     if(s->qscale==0)
 465         return -1;
 466
 467     // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
 468     // subsequent macroblocks, MBA is the difference between the absolute addresses of
 469     // the macroblock and the last transmitted macroblock.
 470     h->current_mba = 0;
 471     h->mba_diff = 0;
 472
 473     return 0;
 474 }
 475
 476 /**
 477  * decodes the group of blocks / video packet header.
 478  * @return <0 if no resync found
 479  */
 480 static int ff_h261_resync(H261Context *h){
 481     MpegEncContext * const s = &h->s;
 482     int left, ret;
 483
 484     if ( h->gob_start_code_skipped ){
 485         ret= h261_decode_gob_header(h);
 486         if(ret>=0)
 487             return 0;
 488     }
 489     else{
 490         if(show_bits(&s->gb, 15)==0){
 491             ret= h261_decode_gob_header(h);
 492             if(ret>=0)
 493                 return 0;
 494         }
 495         //ok, its not where its supposed to be ...
 496         s->gb= s->last_resync_gb;
 497         align_get_bits(&s->gb);
 498         left= s->gb.size_in_bits - get_bits_count(&s->gb);
 499
 500         for(;left>15+1+4+5; left-=8){
 501             if(show_bits(&s->gb, 15)==0){
 502                 GetBitContext bak= s->gb;
 503
 504                 ret= h261_decode_gob_header(h);
 505                 if(ret>=0)
 506                     return 0;
 507
 508                 s->gb= bak;
 509             }
 510             skip_bits(&s->gb, 8);
 511         }
 512     }
 513
 514     return -1;
 515 }
 516
 517 /**
 518  * decodes skipped macroblocks
 519  * @return 0
 520  */
 521 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
 522 {
 523     MpegEncContext * const s = &h->s;
 524     int i;
 525
 526     s->mb_intra = 0;
 527
 528     for(i=mba1; i<mba2; i++){
 529         int j, xy;
 530
 531         s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
 532         s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
 533         xy = s->mb_x + s->mb_y * s->mb_stride;
 534         ff_init_block_index(s);
 535         ff_update_block_index(s);
 536
 537         for(j=0;j<6;j++)
 538             s->block_last_index[j] = -1;
 539
 540         s->mv_dir = MV_DIR_FORWARD;
 541         s->mv_type = MV_TYPE_16X16;
 542         s->current_picture.mb_type[xy]= MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
 543         s->mv[0][0][0] = 0;
 544         s->mv[0][0][1] = 0;
 545         s->mb_skipped = 1;
 546         h->mtype &= ~MB_TYPE_H261_FIL;
 547
 548         MPV_decode_mb(s, s->block);
 549     }
 550
 551     return 0;
 552 }
 553
 554 static int decode_mv_component(GetBitContext *gb, int v){
 555     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
 556
 557     /* check if mv_diff is valid */
 558     if ( mv_diff < 0 )
 559         return v;
 560
 561     mv_diff = mvmap[mv_diff];
 562
 563     if(mv_diff && !get_bits1(gb))
 564         mv_diff= -mv_diff;
 565
 566     v += mv_diff;
 567     if     (v <=-16) v+= 32;
 568     else if(v >= 16) v-= 32;
 569
 570     return v;
 571 }
 572
 573 static int h261_decode_mb(H261Context *h){
 574     MpegEncContext * const s = &h->s;
 575     int i, cbp, xy;
 576
 577     cbp = 63;
 578     // Read mba
 579     do{
 580         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);
 581
 582         /* Check for slice end */
 583         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
 584         if (h->mba_diff == MBA_STARTCODE){ // start code
 585             h->gob_start_code_skipped = 1;
 586             return SLICE_END;
 587         }
 588     }
 589     while( h->mba_diff == MBA_STUFFING ); // stuffing
 590
 591     if ( h->mba_diff < 0 ){
 592         if ( get_bits_count(&s->gb) + 7 >= s->gb.size_in_bits )
 593             return SLICE_END;
 594
 595         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
 596         return SLICE_ERROR;
 597     }
 598
 599     h->mba_diff += 1;
 600     h->current_mba += h->mba_diff;
 601
 602     if ( h->current_mba > MBA_STUFFING )
 603         return SLICE_ERROR;
 604
 605     s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
 606     s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
 607     xy = s->mb_x + s->mb_y * s->mb_stride;
 608     ff_init_block_index(s);
 609     ff_update_block_index(s);
 610
 611     // Read mtype
 612     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
 613     h->mtype = h261_mtype_map[h->mtype];
 614
 615     // Read mquant
 616     if ( IS_QUANT ( h->mtype ) ){
 617         ff_set_qscale(s, get_bits(&s->gb, 5));
 618     }
 619
 620     s->mb_intra = IS_INTRA4x4(h->mtype);
 621
 622     // Read mv
 623     if ( IS_16X16 ( h->mtype ) ){
 624         // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
 625         // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
 626         // following three situations:
 627         // 1) evaluating MVD for macroblocks 1, 12 and 23;
 628         // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
 629         // 3) MTYPE of the previous macroblock was not MC.
 630         if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
 631              ( h->mba_diff != 1))
 632         {
 633             h->current_mv_x = 0;
 634             h->current_mv_y = 0;
 635         }
 636
 637         h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
 638         h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
 639     }else{
 640         h->current_mv_x = 0;
 641         h->current_mv_y = 0;
 642     }
 643
 644     // Read cbp
 645     if ( HAS_CBP( h->mtype ) ){
 646         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
 647     }
 648
 649     if(s->mb_intra){
 650         s->current_picture.mb_type[xy]= MB_TYPE_INTRA;
 651         goto intra;
 652     }
 653
 654     //set motion vectors
 655     s->mv_dir = MV_DIR_FORWARD;
 656     s->mv_type = MV_TYPE_16X16;
 657     s->current_picture.mb_type[xy]= MB_TYPE_16x16 | MB_TYPE_L0;
 658     s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
 659     s->mv[0][0][1] = h->current_mv_y * 2;
 660
 661 intra:
 662     /* decode each block */
 663     if(s->mb_intra || HAS_CBP(h->mtype)){
 664         s->dsp.clear_blocks(s->block[0]);
 665         for (i = 0; i < 6; i++) {
 666             if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
 667                 return SLICE_ERROR;
 668             }
 669             cbp+=cbp;
 670         }
 671     }else{
 672         for (i = 0; i < 6; i++)
 673             s->block_last_index[i]= -1;
 674     }
 675
 676     MPV_decode_mb(s, s->block);
 677
 678     return SLICE_OK;
 679 }
 680
 681 /**
 682  * decodes a macroblock
 683  * @return <0 if an error occured
 684  */
 685 static int h261_decode_block(H261Context * h, DCTELEM * block,
 686                              int n, int coded)
 687 {
 688     MpegEncContext * const s = &h->s;
 689     int code, level, i, j, run;
 690     RLTable *rl = &h261_rl_tcoeff;
 691     const uint8_t *scan_table;
 692
 693     // For the variable length encoding there are two code tables, one being used for
 694     // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
 695     // for all other LEVELs except the first one in INTRA blocks which is fixed length
 696     // coded with 8 bits.
 697     // NOTE: the two code tables only differ in one VLC so we handle that manually.
 698     scan_table = s->intra_scantable.permutated;
 699     if (s->mb_intra){
 700         /* DC coef */
 701         level = get_bits(&s->gb, 8);
 702         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
 703         if((level&0x7F) == 0){
 704             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
 705             return -1;
 706         }
 707         // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
 708         if (level == 255)
 709             level = 128;
 710         block[0] = level;
 711         i = 1;
 712     }else if(coded){
 713         // Run  Level   Code
 714         // EOB                  Not possible for first level when cbp is available (that's why the table is different)
 715         // 0    1               1s
 716         // *    *               0*
 717         int check = show_bits(&s->gb, 2);
 718         i = 0;
 719         if ( check & 0x2 ){
 720             skip_bits(&s->gb, 2);
 721             block[0] = ( check & 0x1 ) ? -1 : 1;
 722             i = 1;
 723         }
 724     }else{
 725         i = 0;
 726     }
 727     if(!coded){
 728         s->block_last_index[n] = i - 1;
 729         return 0;
 730     }
 731     for(;;){
 732         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
 733         if (code < 0){
 734             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
 735             return -1;
 736         }
 737         if (code == rl->n) {
 738             /* escape */
 739             // 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.
 740             run = get_bits(&s->gb, 6);
 741             level = get_sbits(&s->gb, 8);
 742         }else if(code == 0){
 743             break;
 744         }else{
 745             run = rl->table_run[code];
 746             level = rl->table_level[code];
 747             if (get_bits1(&s->gb))
 748                 level = -level;
 749         }
 750         i += run;
 751         if (i >= 64){
 752             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
 753             return -1;
 754         }
 755         j = scan_table[i];
 756         block[j] = level;
 757         i++;
 758     }
 759     s->block_last_index[n] = i-1;
 760     return 0;
 761 }
 762
 763 /**
 764  * decodes the H261 picture header.
 765  * @return <0 if no startcode found
 766  */
 767 static int h261_decode_picture_header(H261Context *h){
 768     MpegEncContext * const s = &h->s;
 769     int format, i;
 770     uint32_t startcode= 0;
 771
 772     for(i= s->gb.size_in_bits - get_bits_count(&s->gb); i>24; i-=1){
 773         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
 774
 775         if(startcode == 0x10)
 776             break;
 777     }
 778
 779     if (startcode != 0x10){
 780         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
 781         return -1;
 782     }
 783
 784     /* temporal reference */
 785     i= get_bits(&s->gb, 5); /* picture timestamp */
 786     if(i < (s->picture_number&31))
 787         i += 32;
 788     s->picture_number = (s->picture_number&~31) + i;
 789
 790     s->avctx->time_base= (AVRational){1001, 30000};
 791     s->current_picture.pts= s->picture_number;
 792
 793
 794     /* PTYPE starts here */
 795     skip_bits1(&s->gb); /* split screen off */
 796     skip_bits1(&s->gb); /* camera  off */
 797     skip_bits1(&s->gb); /* freeze picture release off */
 798
 799     format = get_bits1(&s->gb);
 800
 801     //only 2 formats possible
 802     if (format == 0){//QCIF
 803         s->width = 176;
 804         s->height = 144;
 805         s->mb_width = 11;
 806         s->mb_height = 9;
 807     }else{//CIF
 808         s->width = 352;
 809         s->height = 288;
 810         s->mb_width = 22;
 811         s->mb_height = 18;
 812     }
 813
 814     s->mb_num = s->mb_width * s->mb_height;
 815
 816     skip_bits1(&s->gb); /* still image mode off */
 817     skip_bits1(&s->gb); /* Reserved */
 818
 819     /* PEI */
 820     while (get_bits1(&s->gb) != 0){
 821         skip_bits(&s->gb, 8);
 822     }
 823
 824     // h261 has no I-FRAMES, but if we pass I_TYPE for the first frame, the codec crashes if it does
 825     // not contain all I-blocks (e.g. when a packet is lost)
 826     s->pict_type = P_TYPE;
 827
 828     h->gob_number = 0;
 829     return 0;
 830 }
 831
 832 static int h261_decode_gob(H261Context *h){
 833     MpegEncContext * const s = &h->s;
 834
 835     ff_set_qscale(s, s->qscale);
 836
 837     /* decode mb's */
 838     while(h->current_mba <= MBA_STUFFING)
 839     {
 840         int ret;
 841         /* DCT & quantize */
 842         ret= h261_decode_mb(h);
 843         if(ret<0){
 844             if(ret==SLICE_END){
 845                 h261_decode_mb_skipped(h, h->current_mba, 33);
 846                 return 0;
 847             }
 848             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
 849             return -1;
 850         }
 851
 852         h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
 853     }
 854
 855     return -1;
 856 }
 857
 858 /**
 859  * returns the number of bytes consumed for building the current frame
 860  */
 861 static int get_consumed_bytes(MpegEncContext *s, int buf_size){
 862     int pos= get_bits_count(&s->gb)>>3;
 863     if(pos==0) pos=1; //avoid infinite loops (i doubt thats needed but ...)
 864     if(pos+10>buf_size) pos=buf_size; // oops ;)
 865
 866     return pos;
 867 }
 868
 869 static int h261_decode_frame(AVCodecContext *avctx,
 870                              void *data, int *data_size,
 871                              uint8_t *buf, int buf_size)
 872 {
 873     H261Context *h= avctx->priv_data;
 874     MpegEncContext *s = &h->s;
 875     int ret;
 876     AVFrame *pict = data;
 877
 878 #ifdef DEBUG
 879     av_log(avctx, AV_LOG_DEBUG, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
 880     av_log(avctx, AV_LOG_DEBUG, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
 881 #endif
 882     s->flags= avctx->flags;
 883     s->flags2= avctx->flags2;
 884
 885     h->gob_start_code_skipped=0;
 886
 887 retry:
 888
 889     init_get_bits(&s->gb, buf, buf_size*8);
 890
 891     if(!s->context_initialized){
 892         if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
 893             return -1;
 894     }
 895
 896     //we need to set current_picture_ptr before reading the header, otherwise we cant store anyting im there
 897     if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
 898         int i= ff_find_unused_picture(s, 0);
 899         s->current_picture_ptr= &s->picture[i];
 900     }
 901
 902     ret = h261_decode_picture_header(h);
 903
 904     /* skip if the header was thrashed */
 905     if (ret < 0){
 906         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
 907         return -1;
 908     }
 909
 910     if (s->width != avctx->coded_width || s->height != avctx->coded_height){
 911         ParseContext pc= s->parse_context; //FIXME move these demuxng hack to avformat
 912         s->parse_context.buffer=0;
 913         MPV_common_end(s);
 914         s->parse_context= pc;
 915     }
 916     if (!s->context_initialized) {
 917         avcodec_set_dimensions(avctx, s->width, s->height);
 918
 919         goto retry;
 920     }
 921
 922     // for hurry_up==5
 923     s->current_picture.pict_type= s->pict_type;
 924     s->current_picture.key_frame= s->pict_type == I_TYPE;
 925
 926     /* skip everything if we are in a hurry>=5 */
 927     if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);
 928     if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==B_TYPE)
 929        ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=I_TYPE)
 930        || avctx->skip_frame >= AVDISCARD_ALL)
 931         return get_consumed_bytes(s, buf_size);
 932
 933     if(MPV_frame_start(s, avctx) < 0)
 934         return -1;
 935
 936     ff_er_frame_start(s);
 937
 938     /* decode each macroblock */
 939     s->mb_x=0;
 940     s->mb_y=0;
 941
 942     while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
 943         if(ff_h261_resync(h)<0)
 944             break;
 945         h261_decode_gob(h);
 946     }
 947     MPV_frame_end(s);
 948
 949 assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
 950 assert(s->current_picture.pict_type == s->pict_type);
 951     *pict= *(AVFrame*)s->current_picture_ptr;
 952     ff_print_debug_info(s, pict);
 953
 954     *data_size = sizeof(AVFrame);
 955
 956     return get_consumed_bytes(s, buf_size);
 957 }
 958
 959 static int h261_decode_end(AVCodecContext *avctx)
 960 {
 961     H261Context *h= avctx->priv_data;
 962     MpegEncContext *s = &h->s;
 963
 964     MPV_common_end(s);
 965     return 0;
 966 }
 967
 968 #ifdef CONFIG_ENCODERS
 969 AVCodec h261_encoder = {
 970     "h261",
 971     CODEC_TYPE_VIDEO,
 972     CODEC_ID_H261,
 973     sizeof(H261Context),
 974     MPV_encode_init,
 975     MPV_encode_picture,
 976     MPV_encode_end,
 977     .pix_fmts= (enum PixelFormat[]){PIX_FMT_YUV420P, -1},
 978 };
 979 #endif
 980
 981 AVCodec h261_decoder = {
 982     "h261",
 983     CODEC_TYPE_VIDEO,
 984     CODEC_ID_H261,
 985     sizeof(H261Context),
 986     h261_decode_init,
 987     NULL,
 988     h261_decode_end,
 989     h261_decode_frame,
 990     CODEC_CAP_DR1,
 991 };