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 av_cold 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, 552);
  70     }
  71 }
  72
  73 static av_cold 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 occurred
 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         av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
 138         if (s->avctx->error_recognition >= FF_ER_COMPLIANT)
 139             return -1;
 140     }
 141
 142     // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
 143     // subsequent macroblocks, MBA is the difference between the absolute addresses of
 144     // the macroblock and the last transmitted macroblock.
 145     h->current_mba = 0;
 146     h->mba_diff = 0;
 147
 148     return 0;
 149 }
 150
 151 /**
 152  * decodes the group of blocks / video packet header.
 153  * @return <0 if no resync found
 154  */
 155 static int ff_h261_resync(H261Context *h){
 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     }
 164     else{
 165         if(show_bits(&s->gb, 15)==0){
 166             ret= h261_decode_gob_header(h);
 167             if(ret>=0)
 168                 return 0;
 169         }
 170         //OK, it is not where it is supposed to be ...
 171         s->gb= s->last_resync_gb;
 172         align_get_bits(&s->gb);
 173         left= s->gb.size_in_bits - get_bits_count(&s->gb);
 174
 175         for(;left>15+1+4+5; left-=8){
 176             if(show_bits(&s->gb, 15)==0){
 177                 GetBitContext bak= s->gb;
 178
 179                 ret= h261_decode_gob_header(h);
 180                 if(ret>=0)
 181                     return 0;
 182
 183                 s->gb= bak;
 184             }
 185             skip_bits(&s->gb, 8);
 186         }
 187     }
 188
 189     return -1;
 190 }
 191
 192 /**
 193  * decodes skipped macroblocks
 194  * @return 0
 195  */
 196 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
 197 {
 198     MpegEncContext * const s = &h->s;
 199     int i;
 200
 201     s->mb_intra = 0;
 202
 203     for(i=mba1; i<mba2; i++){
 204         int j, xy;
 205
 206         s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
 207         s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
 208         xy = s->mb_x + s->mb_y * s->mb_stride;
 209         ff_init_block_index(s);
 210         ff_update_block_index(s);
 211
 212         for(j=0;j<6;j++)
 213             s->block_last_index[j] = -1;
 214
 215         s->mv_dir = MV_DIR_FORWARD;
 216         s->mv_type = MV_TYPE_16X16;
 217         s->current_picture.mb_type[xy]= MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
 218         s->mv[0][0][0] = 0;
 219         s->mv[0][0][1] = 0;
 220         s->mb_skipped = 1;
 221         h->mtype &= ~MB_TYPE_H261_FIL;
 222
 223         MPV_decode_mb(s, s->block);
 224     }
 225
 226     return 0;
 227 }
 228
 229 static int decode_mv_component(GetBitContext *gb, int v){
 230     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
 231
 232     /* check if mv_diff is valid */
 233     if ( mv_diff < 0 )
 234         return v;
 235
 236     mv_diff = mvmap[mv_diff];
 237
 238     if(mv_diff && !get_bits1(gb))
 239         mv_diff= -mv_diff;
 240
 241     v += mv_diff;
 242     if     (v <=-16) v+= 32;
 243     else if(v >= 16) v-= 32;
 244
 245     return v;
 246 }
 247
 248 static int h261_decode_mb(H261Context *h){
 249     MpegEncContext * const s = &h->s;
 250     int i, cbp, xy;
 251
 252     cbp = 63;
 253     // Read mba
 254     do{
 255         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);
 256
 257         /* Check for slice end */
 258         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
 259         if (h->mba_diff == MBA_STARTCODE){ // start code
 260             h->gob_start_code_skipped = 1;
 261             return SLICE_END;
 262         }
 263     }
 264     while( h->mba_diff == MBA_STUFFING ); // stuffing
 265
 266     if ( h->mba_diff < 0 ){
 267         if ( get_bits_count(&s->gb) + 7 >= s->gb.size_in_bits )
 268             return SLICE_END;
 269
 270         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
 271         return SLICE_ERROR;
 272     }
 273
 274     h->mba_diff += 1;
 275     h->current_mba += h->mba_diff;
 276
 277     if ( h->current_mba > MBA_STUFFING )
 278         return SLICE_ERROR;
 279
 280     s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
 281     s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
 282     xy = s->mb_x + s->mb_y * s->mb_stride;
 283     ff_init_block_index(s);
 284     ff_update_block_index(s);
 285
 286     // Read mtype
 287     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
 288     h->mtype = h261_mtype_map[h->mtype];
 289
 290     // Read mquant
 291     if ( IS_QUANT ( h->mtype ) ){
 292         ff_set_qscale(s, get_bits(&s->gb, 5));
 293     }
 294
 295     s->mb_intra = IS_INTRA4x4(h->mtype);
 296
 297     // Read mv
 298     if ( IS_16X16 ( h->mtype ) ){
 299         // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
 300         // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
 301         // following three situations:
 302         // 1) evaluating MVD for macroblocks 1, 12 and 23;
 303         // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
 304         // 3) MTYPE of the previous macroblock was not MC.
 305         if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
 306              ( h->mba_diff != 1))
 307         {
 308             h->current_mv_x = 0;
 309             h->current_mv_y = 0;
 310         }
 311
 312         h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
 313         h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
 314     }else{
 315         h->current_mv_x = 0;
 316         h->current_mv_y = 0;
 317     }
 318
 319     // Read cbp
 320     if ( HAS_CBP( h->mtype ) ){
 321         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
 322     }
 323
 324     if(s->mb_intra){
 325         s->current_picture.mb_type[xy]= MB_TYPE_INTRA;
 326         goto intra;
 327     }
 328
 329     //set motion vectors
 330     s->mv_dir = MV_DIR_FORWARD;
 331     s->mv_type = MV_TYPE_16X16;
 332     s->current_picture.mb_type[xy]= MB_TYPE_16x16 | MB_TYPE_L0;
 333     s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
 334     s->mv[0][0][1] = h->current_mv_y * 2;
 335
 336 intra:
 337     /* decode each block */
 338     if(s->mb_intra || HAS_CBP(h->mtype)){
 339         s->dsp.clear_blocks(s->block[0]);
 340         for (i = 0; i < 6; i++) {
 341             if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
 342                 return SLICE_ERROR;
 343             }
 344             cbp+=cbp;
 345         }
 346     }else{
 347         for (i = 0; i < 6; i++)
 348             s->block_last_index[i]= -1;
 349     }
 350
 351     MPV_decode_mb(s, s->block);
 352
 353     return SLICE_OK;
 354 }
 355
 356 /**
 357  * decodes a macroblock
 358  * @return <0 if an error occurred
 359  */
 360 static int h261_decode_block(H261Context * h, DCTELEM * block,
 361                              int n, int coded)
 362 {
 363     MpegEncContext * const s = &h->s;
 364     int code, level, i, j, run;
 365     RLTable *rl = &h261_rl_tcoeff;
 366     const uint8_t *scan_table;
 367
 368     // For the variable length encoding there are two code tables, one being used for
 369     // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
 370     // for all other LEVELs except the first one in INTRA blocks which is fixed length
 371     // coded with 8 bits.
 372     // NOTE: the two code tables only differ in one VLC so we handle that manually.
 373     scan_table = s->intra_scantable.permutated;
 374     if (s->mb_intra){
 375         /* DC coef */
 376         level = get_bits(&s->gb, 8);
 377         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
 378         if((level&0x7F) == 0){
 379             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
 380             return -1;
 381         }
 382         // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
 383         if (level == 255)
 384             level = 128;
 385         block[0] = level;
 386         i = 1;
 387     }else if(coded){
 388         // Run  Level   Code
 389         // EOB                  Not possible for first level when cbp is available (that's why the table is different)
 390         // 0    1               1s
 391         // *    *               0*
 392         int check = show_bits(&s->gb, 2);
 393         i = 0;
 394         if ( check & 0x2 ){
 395             skip_bits(&s->gb, 2);
 396             block[0] = ( check & 0x1 ) ? -1 : 1;
 397             i = 1;
 398         }
 399     }else{
 400         i = 0;
 401     }
 402     if(!coded){
 403         s->block_last_index[n] = i - 1;
 404         return 0;
 405     }
 406     for(;;){
 407         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
 408         if (code < 0){
 409             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
 410             return -1;
 411         }
 412         if (code == rl->n) {
 413             /* escape */
 414             // 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.
 415             run = get_bits(&s->gb, 6);
 416             level = get_sbits(&s->gb, 8);
 417         }else if(code == 0){
 418             break;
 419         }else{
 420             run = rl->table_run[code];
 421             level = rl->table_level[code];
 422             if (get_bits1(&s->gb))
 423                 level = -level;
 424         }
 425         i += run;
 426         if (i >= 64){
 427             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
 428             return -1;
 429         }
 430         j = scan_table[i];
 431         block[j] = level;
 432         i++;
 433     }
 434     s->block_last_index[n] = i-1;
 435     return 0;
 436 }
 437
 438 /**
 439  * decodes the H261 picture header.
 440  * @return <0 if no startcode found
 441  */
 442 static int h261_decode_picture_header(H261Context *h){
 443     MpegEncContext * const s = &h->s;
 444     int format, i;
 445     uint32_t startcode= 0;
 446
 447     for(i= s->gb.size_in_bits - get_bits_count(&s->gb); i>24; i-=1){
 448         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
 449
 450         if(startcode == 0x10)
 451             break;
 452     }
 453
 454     if (startcode != 0x10){
 455         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
 456         return -1;
 457     }
 458
 459     /* temporal reference */
 460     i= get_bits(&s->gb, 5); /* picture timestamp */
 461     if(i < (s->picture_number&31))
 462         i += 32;
 463     s->picture_number = (s->picture_number&~31) + i;
 464
 465     s->avctx->time_base= (AVRational){1001, 30000};
 466     s->current_picture.pts= s->picture_number;
 467
 468
 469     /* PTYPE starts here */
 470     skip_bits1(&s->gb); /* split screen off */
 471     skip_bits1(&s->gb); /* camera  off */
 472     skip_bits1(&s->gb); /* freeze picture release off */
 473
 474     format = get_bits1(&s->gb);
 475
 476     //only 2 formats possible
 477     if (format == 0){//QCIF
 478         s->width = 176;
 479         s->height = 144;
 480         s->mb_width = 11;
 481         s->mb_height = 9;
 482     }else{//CIF
 483         s->width = 352;
 484         s->height = 288;
 485         s->mb_width = 22;
 486         s->mb_height = 18;
 487     }
 488
 489     s->mb_num = s->mb_width * s->mb_height;
 490
 491     skip_bits1(&s->gb); /* still image mode off */
 492     skip_bits1(&s->gb); /* Reserved */
 493
 494     /* PEI */
 495     while (get_bits1(&s->gb) != 0){
 496         skip_bits(&s->gb, 8);
 497     }
 498
 499     // h261 has no I-FRAMES, but if we pass FF_I_TYPE for the first frame, the codec crashes if it does
 500     // not contain all I-blocks (e.g. when a packet is lost)
 501     s->pict_type = FF_P_TYPE;
 502
 503     h->gob_number = 0;
 504     return 0;
 505 }
 506
 507 static int h261_decode_gob(H261Context *h){
 508     MpegEncContext * const s = &h->s;
 509
 510     ff_set_qscale(s, s->qscale);
 511
 512     /* decode mb's */
 513     while(h->current_mba <= MBA_STUFFING)
 514     {
 515         int ret;
 516         /* DCT & quantize */
 517         ret= h261_decode_mb(h);
 518         if(ret<0){
 519             if(ret==SLICE_END){
 520                 h261_decode_mb_skipped(h, h->current_mba, 33);
 521                 return 0;
 522             }
 523             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
 524             return -1;
 525         }
 526
 527         h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
 528     }
 529
 530     return -1;
 531 }
 532
 533 /**
 534  * returns the number of bytes consumed for building the current frame
 535  */
 536 static int get_consumed_bytes(MpegEncContext *s, int buf_size){
 537     int pos= get_bits_count(&s->gb)>>3;
 538     if(pos==0) pos=1; //avoid infinite loops (i doubt that is needed but ...)
 539     if(pos+10>buf_size) pos=buf_size; // oops ;)
 540
 541     return pos;
 542 }
 543
 544 static int h261_decode_frame(AVCodecContext *avctx,
 545                              void *data, int *data_size,
 546                              const uint8_t *buf, int buf_size)
 547 {
 548     H261Context *h= avctx->priv_data;
 549     MpegEncContext *s = &h->s;
 550     int ret;
 551     AVFrame *pict = data;
 552
 553 #ifdef DEBUG
 554     av_log(avctx, AV_LOG_DEBUG, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
 555     av_log(avctx, AV_LOG_DEBUG, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
 556 #endif
 557     s->flags= avctx->flags;
 558     s->flags2= avctx->flags2;
 559
 560     h->gob_start_code_skipped=0;
 561
 562 retry:
 563
 564     init_get_bits(&s->gb, buf, buf_size*8);
 565
 566     if(!s->context_initialized){
 567         if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
 568             return -1;
 569     }
 570
 571     //we need to set current_picture_ptr before reading the header, otherwise we cannot store anyting im there
 572     if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
 573         int i= ff_find_unused_picture(s, 0);
 574         s->current_picture_ptr= &s->picture[i];
 575     }
 576
 577     ret = h261_decode_picture_header(h);
 578
 579     /* skip if the header was thrashed */
 580     if (ret < 0){
 581         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
 582         return -1;
 583     }
 584
 585     if (s->width != avctx->coded_width || s->height != avctx->coded_height){
 586         ParseContext pc= s->parse_context; //FIXME move this demuxing hack to libavformat
 587         s->parse_context.buffer=0;
 588         MPV_common_end(s);
 589         s->parse_context= pc;
 590     }
 591     if (!s->context_initialized) {
 592         avcodec_set_dimensions(avctx, s->width, s->height);
 593
 594         goto retry;
 595     }
 596
 597     // for hurry_up==5
 598     s->current_picture.pict_type= s->pict_type;
 599     s->current_picture.key_frame= s->pict_type == FF_I_TYPE;
 600
 601     /* skip everything if we are in a hurry>=5 */
 602     if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);
 603     if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==FF_B_TYPE)
 604        ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=FF_I_TYPE)
 605        || avctx->skip_frame >= AVDISCARD_ALL)
 606         return get_consumed_bytes(s, buf_size);
 607
 608     if(MPV_frame_start(s, avctx) < 0)
 609         return -1;
 610
 611     ff_er_frame_start(s);
 612
 613     /* decode each macroblock */
 614     s->mb_x=0;
 615     s->mb_y=0;
 616
 617     while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
 618         if(ff_h261_resync(h)<0)
 619             break;
 620         h261_decode_gob(h);
 621     }
 622     MPV_frame_end(s);
 623
 624 assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
 625 assert(s->current_picture.pict_type == s->pict_type);
 626     *pict= *(AVFrame*)s->current_picture_ptr;
 627     ff_print_debug_info(s, pict);
 628
 629     *data_size = sizeof(AVFrame);
 630
 631     return get_consumed_bytes(s, buf_size);
 632 }
 633
 634 static av_cold int h261_decode_end(AVCodecContext *avctx)
 635 {
 636     H261Context *h= avctx->priv_data;
 637     MpegEncContext *s = &h->s;
 638
 639     MPV_common_end(s);
 640     return 0;
 641 }
 642
 643 AVCodec h261_decoder = {
 644     "h261",
 645     CODEC_TYPE_VIDEO,
 646     CODEC_ID_H261,
 647     sizeof(H261Context),
 648     h261_decode_init,
 649     NULL,
 650     h261_decode_end,
 651     h261_decode_frame,
 652     CODEC_CAP_DR1,
 653     .long_name = NULL_IF_CONFIG_SMALL("H.261"),
 654 };