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 Libav.
   7  *
   8  * Libav 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  * Libav 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 Libav; 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 "dsputil.h"
  29 #include "avcodec.h"
  30 #include "mpegvideo.h"
  31 #include "h263.h"
  32 #include "h261.h"
  33 #include "h261data.h"
  34
  35 #define H261_MBA_VLC_BITS 9
  36 #define H261_MTYPE_VLC_BITS 6
  37 #define H261_MV_VLC_BITS 7
  38 #define H261_CBP_VLC_BITS 9
  39 #define TCOEFF_VLC_BITS 9
  40 #define MBA_STUFFING 33
  41 #define MBA_STARTCODE 34
  42
  43 extern uint8_t ff_h261_rl_table_store[2][2*MAX_RUN + MAX_LEVEL + 3];
  44
  45 static VLC h261_mba_vlc;
  46 static VLC h261_mtype_vlc;
  47 static VLC h261_mv_vlc;
  48 static VLC h261_cbp_vlc;
  49
  50 static int h261_decode_block(H261Context * h, int16_t * block, int n, int coded);
  51
  52 static av_cold void h261_decode_init_vlc(H261Context *h){
  53     static int done = 0;
  54
  55     if(!done){
  56         done = 1;
  57         INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
  58                  h261_mba_bits, 1, 1,
  59                  h261_mba_code, 1, 1, 662);
  60         INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
  61                  h261_mtype_bits, 1, 1,
  62                  h261_mtype_code, 1, 1, 80);
  63         INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
  64                  &h261_mv_tab[0][1], 2, 1,
  65                  &h261_mv_tab[0][0], 2, 1, 144);
  66         INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
  67                  &h261_cbp_tab[0][1], 2, 1,
  68                  &h261_cbp_tab[0][0], 2, 1, 512);
  69         ff_init_rl(&h261_rl_tcoeff, ff_h261_rl_table_store);
  70         INIT_VLC_RL(h261_rl_tcoeff, 552);
  71     }
  72 }
  73
  74 static av_cold int h261_decode_init(AVCodecContext *avctx){
  75     H261Context *h= avctx->priv_data;
  76     MpegEncContext * const s = &h->s;
  77
  78     // set defaults
  79     ff_MPV_decode_defaults(s);
  80     s->avctx = avctx;
  81
  82     s->width  = s->avctx->coded_width;
  83     s->height = s->avctx->coded_height;
  84     s->codec_id = s->avctx->codec->id;
  85
  86     s->out_format = FMT_H261;
  87     s->low_delay= 1;
  88     avctx->pix_fmt= AV_PIX_FMT_YUV420P;
  89
  90     s->codec_id= avctx->codec->id;
  91
  92     h261_decode_init_vlc(h);
  93
  94     h->gob_start_code_skipped = 0;
  95
  96     return 0;
  97 }
  98
  99 /**
 100  * Decode the group of blocks header or slice header.
 101  * @return <0 if an error occurred
 102  */
 103 static int h261_decode_gob_header(H261Context *h){
 104     unsigned int val;
 105     MpegEncContext * const s = &h->s;
 106
 107     if ( !h->gob_start_code_skipped ){
 108         /* Check for GOB Start Code */
 109         val = show_bits(&s->gb, 15);
 110         if(val)
 111             return -1;
 112
 113         /* We have a GBSC */
 114         skip_bits(&s->gb, 16);
 115     }
 116
 117     h->gob_start_code_skipped = 0;
 118
 119     h->gob_number = get_bits(&s->gb, 4); /* GN */
 120     s->qscale = get_bits(&s->gb, 5); /* GQUANT */
 121
 122     /* Check if gob_number is valid */
 123     if (s->mb_height==18){ //cif
 124         if ((h->gob_number<=0) || (h->gob_number>12))
 125             return -1;
 126     }
 127     else{ //qcif
 128         if ((h->gob_number!=1) && (h->gob_number!=3) && (h->gob_number!=5))
 129             return -1;
 130     }
 131
 132     /* GEI */
 133     while (get_bits1(&s->gb) != 0) {
 134         skip_bits(&s->gb, 8);
 135     }
 136
 137     if(s->qscale==0) {
 138         av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
 139         if (s->avctx->err_recognition & AV_EF_BITSTREAM)
 140             return -1;
 141     }
 142
 143     // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
 144     // subsequent macroblocks, MBA is the difference between the absolute addresses of
 145     // the macroblock and the last transmitted macroblock.
 146     h->current_mba = 0;
 147     h->mba_diff = 0;
 148
 149     return 0;
 150 }
 151
 152 /**
 153  * Decode the group of blocks / video packet header.
 154  * @return <0 if no resync found
 155  */
 156 static int ff_h261_resync(H261Context *h){
 157     MpegEncContext * const s = &h->s;
 158     int left, ret;
 159
 160     if ( h->gob_start_code_skipped ){
 161         ret= h261_decode_gob_header(h);
 162         if(ret>=0)
 163             return 0;
 164     }
 165     else{
 166         if(show_bits(&s->gb, 15)==0){
 167             ret= h261_decode_gob_header(h);
 168             if(ret>=0)
 169                 return 0;
 170         }
 171         //OK, it is not where it is supposed to be ...
 172         s->gb= s->last_resync_gb;
 173         align_get_bits(&s->gb);
 174         left= get_bits_left(&s->gb);
 175
 176         for(;left>15+1+4+5; left-=8){
 177             if(show_bits(&s->gb, 15)==0){
 178                 GetBitContext bak= s->gb;
 179
 180                 ret= h261_decode_gob_header(h);
 181                 if(ret>=0)
 182                     return 0;
 183
 184                 s->gb= bak;
 185             }
 186             skip_bits(&s->gb, 8);
 187         }
 188     }
 189
 190     return -1;
 191 }
 192
 193 /**
 194  * Decode skipped macroblocks.
 195  * @return 0
 196  */
 197 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
 198 {
 199     MpegEncContext * const s = &h->s;
 200     int i;
 201
 202     s->mb_intra = 0;
 203
 204     for(i=mba1; i<mba2; i++){
 205         int j, xy;
 206
 207         s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
 208         s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
 209         xy = s->mb_x + s->mb_y * s->mb_stride;
 210         ff_init_block_index(s);
 211         ff_update_block_index(s);
 212
 213         for(j=0;j<6;j++)
 214             s->block_last_index[j] = -1;
 215
 216         s->mv_dir = MV_DIR_FORWARD;
 217         s->mv_type = MV_TYPE_16X16;
 218         s->current_picture.f.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
 219         s->mv[0][0][0] = 0;
 220         s->mv[0][0][1] = 0;
 221         s->mb_skipped = 1;
 222         h->mtype &= ~MB_TYPE_H261_FIL;
 223
 224         ff_MPV_decode_mb(s, s->block);
 225     }
 226
 227     return 0;
 228 }
 229
 230 static int decode_mv_component(GetBitContext *gb, int v){
 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) v+= 32;
 244     else if(v >= 16) v-= 32;
 245
 246     return v;
 247 }
 248
 249 static int h261_decode_mb(H261Context *h){
 250     MpegEncContext * const s = &h->s;
 251     int i, cbp, xy;
 252
 253     cbp = 63;
 254     // Read mba
 255     do{
 256         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);
 257
 258         /* Check for slice end */
 259         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
 260         if (h->mba_diff == MBA_STARTCODE){ // start code
 261             h->gob_start_code_skipped = 1;
 262             return SLICE_END;
 263         }
 264     }
 265     while( h->mba_diff == MBA_STUFFING ); // stuffing
 266
 267     if ( h->mba_diff < 0 ){
 268         if (get_bits_left(&s->gb) <= 7)
 269             return SLICE_END;
 270
 271         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
 272         return SLICE_ERROR;
 273     }
 274
 275     h->mba_diff += 1;
 276     h->current_mba += h->mba_diff;
 277
 278     if ( h->current_mba > MBA_STUFFING )
 279         return SLICE_ERROR;
 280
 281     s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
 282     s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
 283     xy = s->mb_x + s->mb_y * s->mb_stride;
 284     ff_init_block_index(s);
 285     ff_update_block_index(s);
 286
 287     // Read mtype
 288     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
 289     h->mtype = h261_mtype_map[h->mtype];
 290
 291     // Read mquant
 292     if ( IS_QUANT ( h->mtype ) ){
 293         ff_set_qscale(s, get_bits(&s->gb, 5));
 294     }
 295
 296     s->mb_intra = IS_INTRA4x4(h->mtype);
 297
 298     // Read mv
 299     if ( IS_16X16 ( h->mtype ) ){
 300         // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
 301         // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
 302         // following three situations:
 303         // 1) evaluating MVD for macroblocks 1, 12 and 23;
 304         // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
 305         // 3) MTYPE of the previous macroblock was not MC.
 306         if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
 307              ( h->mba_diff != 1))
 308         {
 309             h->current_mv_x = 0;
 310             h->current_mv_y = 0;
 311         }
 312
 313         h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
 314         h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
 315     }else{
 316         h->current_mv_x = 0;
 317         h->current_mv_y = 0;
 318     }
 319
 320     // Read cbp
 321     if ( HAS_CBP( h->mtype ) ){
 322         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
 323     }
 324
 325     if(s->mb_intra){
 326         s->current_picture.f.mb_type[xy] = MB_TYPE_INTRA;
 327         goto intra;
 328     }
 329
 330     //set motion vectors
 331     s->mv_dir = MV_DIR_FORWARD;
 332     s->mv_type = MV_TYPE_16X16;
 333     s->current_picture.f.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;
 334     s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
 335     s->mv[0][0][1] = h->current_mv_y * 2;
 336
 337 intra:
 338     /* decode each block */
 339     if(s->mb_intra || HAS_CBP(h->mtype)){
 340         s->dsp.clear_blocks(s->block[0]);
 341         for (i = 0; i < 6; i++) {
 342             if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
 343                 return SLICE_ERROR;
 344             }
 345             cbp+=cbp;
 346         }
 347     }else{
 348         for (i = 0; i < 6; i++)
 349             s->block_last_index[i]= -1;
 350     }
 351
 352     ff_MPV_decode_mb(s, s->block);
 353
 354     return SLICE_OK;
 355 }
 356
 357 /**
 358  * Decode a macroblock.
 359  * @return <0 if an error occurred
 360  */
 361 static int h261_decode_block(H261Context * h, int16_t * block,
 362                              int n, int coded)
 363 {
 364     MpegEncContext * const s = &h->s;
 365     int code, level, i, j, run;
 366     RLTable *rl = &h261_rl_tcoeff;
 367     const uint8_t *scan_table;
 368
 369     // For the variable length encoding there are two code tables, one being used for
 370     // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
 371     // for all other LEVELs except the first one in INTRA blocks which is fixed length
 372     // coded with 8 bits.
 373     // NOTE: the two code tables only differ in one VLC so we handle that manually.
 374     scan_table = s->intra_scantable.permutated;
 375     if (s->mb_intra){
 376         /* DC coef */
 377         level = get_bits(&s->gb, 8);
 378         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
 379         if((level&0x7F) == 0){
 380             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
 381             return -1;
 382         }
 383         // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
 384         if (level == 255)
 385             level = 128;
 386         block[0] = level;
 387         i = 1;
 388     }else if(coded){
 389         // Run  Level   Code
 390         // EOB                  Not possible for first level when cbp is available (that's why the table is different)
 391         // 0    1               1s
 392         // *    *               0*
 393         int check = show_bits(&s->gb, 2);
 394         i = 0;
 395         if ( check & 0x2 ){
 396             skip_bits(&s->gb, 2);
 397             block[0] = ( check & 0x1 ) ? -1 : 1;
 398             i = 1;
 399         }
 400     }else{
 401         i = 0;
 402     }
 403     if(!coded){
 404         s->block_last_index[n] = i - 1;
 405         return 0;
 406     }
 407     for(;;){
 408         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
 409         if (code < 0){
 410             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
 411             return -1;
 412         }
 413         if (code == rl->n) {
 414             /* escape */
 415             // 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.
 416             run = get_bits(&s->gb, 6);
 417             level = get_sbits(&s->gb, 8);
 418         }else if(code == 0){
 419             break;
 420         }else{
 421             run = rl->table_run[code];
 422             level = rl->table_level[code];
 423             if (get_bits1(&s->gb))
 424                 level = -level;
 425         }
 426         i += run;
 427         if (i >= 64){
 428             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
 429             return -1;
 430         }
 431         j = scan_table[i];
 432         block[j] = level;
 433         i++;
 434     }
 435     s->block_last_index[n] = i-1;
 436     return 0;
 437 }
 438
 439 /**
 440  * Decode the H.261 picture header.
 441  * @return <0 if no startcode found
 442  */
 443 static int h261_decode_picture_header(H261Context *h){
 444     MpegEncContext * const s = &h->s;
 445     int format, i;
 446     uint32_t startcode= 0;
 447
 448     for(i= get_bits_left(&s->gb); i>24; i-=1){
 449         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
 450
 451         if(startcode == 0x10)
 452             break;
 453     }
 454
 455     if (startcode != 0x10){
 456         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
 457         return -1;
 458     }
 459
 460     /* temporal reference */
 461     i= get_bits(&s->gb, 5); /* picture timestamp */
 462     if(i < (s->picture_number&31))
 463         i += 32;
 464     s->picture_number = (s->picture_number&~31) + i;
 465
 466     s->avctx->time_base= (AVRational){1001, 30000};
 467     s->current_picture.f.pts = s->picture_number;
 468
 469
 470     /* PTYPE starts here */
 471     skip_bits1(&s->gb); /* split screen off */
 472     skip_bits1(&s->gb); /* camera  off */
 473     skip_bits1(&s->gb); /* freeze picture release off */
 474
 475     format = get_bits1(&s->gb);
 476
 477     //only 2 formats possible
 478     if (format == 0){//QCIF
 479         s->width = 176;
 480         s->height = 144;
 481         s->mb_width = 11;
 482         s->mb_height = 9;
 483     }else{//CIF
 484         s->width = 352;
 485         s->height = 288;
 486         s->mb_width = 22;
 487         s->mb_height = 18;
 488     }
 489
 490     s->mb_num = s->mb_width * s->mb_height;
 491
 492     skip_bits1(&s->gb); /* still image mode off */
 493     skip_bits1(&s->gb); /* Reserved */
 494
 495     /* PEI */
 496     while (get_bits1(&s->gb) != 0){
 497         skip_bits(&s->gb, 8);
 498     }
 499
 500     // h261 has no I-FRAMES, but if we pass AV_PICTURE_TYPE_I for the first frame, the codec crashes if it does
 501     // not contain all I-blocks (e.g. when a packet is lost)
 502     s->pict_type = AV_PICTURE_TYPE_P;
 503
 504     h->gob_number = 0;
 505     return 0;
 506 }
 507
 508 static int h261_decode_gob(H261Context *h){
 509     MpegEncContext * const s = &h->s;
 510
 511     ff_set_qscale(s, s->qscale);
 512
 513     /* decode mb's */
 514     while(h->current_mba <= MBA_STUFFING)
 515     {
 516         int ret;
 517         /* DCT & quantize */
 518         ret= h261_decode_mb(h);
 519         if(ret<0){
 520             if(ret==SLICE_END){
 521                 h261_decode_mb_skipped(h, h->current_mba, 33);
 522                 return 0;
 523             }
 524             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
 525             return -1;
 526         }
 527
 528         h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
 529     }
 530
 531     return -1;
 532 }
 533
 534 /**
 535  * returns the number of bytes consumed for building the current frame
 536  */
 537 static int get_consumed_bytes(MpegEncContext *s, int buf_size){
 538     int pos= get_bits_count(&s->gb)>>3;
 539     if(pos==0) pos=1; //avoid infinite loops (i doubt that is needed but ...)
 540     if(pos+10>buf_size) pos=buf_size; // oops ;)
 541
 542     return pos;
 543 }
 544
 545 static int h261_decode_frame(AVCodecContext *avctx,
 546                              void *data, int *got_frame,
 547                              AVPacket *avpkt)
 548 {
 549     const uint8_t *buf = avpkt->data;
 550     int buf_size = avpkt->size;
 551     H261Context *h= avctx->priv_data;
 552     MpegEncContext *s = &h->s;
 553     int ret;
 554     AVFrame *pict = data;
 555
 556     av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
 557     av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
 558     s->flags= avctx->flags;
 559     s->flags2= avctx->flags2;
 560
 561     h->gob_start_code_skipped=0;
 562
 563 retry:
 564
 565     init_get_bits(&s->gb, buf, buf_size*8);
 566
 567     if(!s->context_initialized){
 568         if (ff_MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
 569             return -1;
 570     }
 571
 572     //we need to set current_picture_ptr before reading the header, otherwise we cannot store anyting im there
 573     if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
 574         int i= ff_find_unused_picture(s, 0);
 575         if (i < 0)
 576             return i;
 577         s->current_picture_ptr= &s->picture[i];
 578     }
 579
 580     ret = h261_decode_picture_header(h);
 581
 582     /* skip if the header was thrashed */
 583     if (ret < 0){
 584         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
 585         return -1;
 586     }
 587
 588     if (s->width != avctx->coded_width || s->height != avctx->coded_height){
 589         ParseContext pc= s->parse_context; //FIXME move this demuxing hack to libavformat
 590         s->parse_context.buffer=0;
 591         ff_MPV_common_end(s);
 592         s->parse_context= pc;
 593     }
 594     if (!s->context_initialized) {
 595         avcodec_set_dimensions(avctx, s->width, s->height);
 596
 597         goto retry;
 598     }
 599
 600     // for skipping the frame
 601     s->current_picture.f.pict_type = s->pict_type;
 602     s->current_picture.f.key_frame = s->pict_type == AV_PICTURE_TYPE_I;
 603
 604     if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==AV_PICTURE_TYPE_B)
 605        ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=AV_PICTURE_TYPE_I)
 606        || avctx->skip_frame >= AVDISCARD_ALL)
 607         return get_consumed_bytes(s, buf_size);
 608
 609     if(ff_MPV_frame_start(s, avctx) < 0)
 610         return -1;
 611
 612     ff_er_frame_start(s);
 613
 614     /* decode each macroblock */
 615     s->mb_x=0;
 616     s->mb_y=0;
 617
 618     while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
 619         if(ff_h261_resync(h)<0)
 620             break;
 621         h261_decode_gob(h);
 622     }
 623     ff_MPV_frame_end(s);
 624
 625 assert(s->current_picture.f.pict_type == s->current_picture_ptr->f.pict_type);
 626 assert(s->current_picture.f.pict_type == s->pict_type);
 627
 628     *pict = s->current_picture_ptr->f;
 629     ff_print_debug_info(s, pict);
 630
 631     *got_frame = 1;
 632
 633     return get_consumed_bytes(s, buf_size);
 634 }
 635
 636 static av_cold int h261_decode_end(AVCodecContext *avctx)
 637 {
 638     H261Context *h= avctx->priv_data;
 639     MpegEncContext *s = &h->s;
 640
 641     ff_MPV_common_end(s);
 642     return 0;
 643 }
 644
 645 AVCodec ff_h261_decoder = {
 646     .name           = "h261",
 647     .type           = AVMEDIA_TYPE_VIDEO,
 648     .id             = AV_CODEC_ID_H261,
 649     .priv_data_size = sizeof(H261Context),
 650     .init           = h261_decode_init,
 651     .close          = h261_decode_end,
 652     .decode         = h261_decode_frame,
 653     .capabilities   = CODEC_CAP_DR1,
 654     .long_name      = NULL_IF_CONFIG_SMALL("H.261"),
 655 };