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libavcodec/h261dec.c

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00001 /*
00002  * H261 decoder
00003  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
00004  * Copyright (c) 2004 Maarten Daniels
00005  *
00006  * This file is part of FFmpeg.
00007  *
00008  * FFmpeg is free software; you can redistribute it and/or
00009  * modify it under the terms of the GNU Lesser General Public
00010  * License as published by the Free Software Foundation; either
00011  * version 2.1 of the License, or (at your option) any later version.
00012  *
00013  * FFmpeg is distributed in the hope that it will be useful,
00014  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00016  * Lesser General Public License for more details.
00017  *
00018  * You should have received a copy of the GNU Lesser General Public
00019  * License along with FFmpeg; if not, write to the Free Software
00020  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00021  */
00022 
00028 #include "dsputil.h"
00029 #include "avcodec.h"
00030 #include "mpegvideo.h"
00031 #include "h263.h"
00032 #include "h261.h"
00033 #include "h261data.h"
00034 
00035 #define H261_MBA_VLC_BITS 9
00036 #define H261_MTYPE_VLC_BITS 6
00037 #define H261_MV_VLC_BITS 7
00038 #define H261_CBP_VLC_BITS 9
00039 #define TCOEFF_VLC_BITS 9
00040 #define MBA_STUFFING 33
00041 #define MBA_STARTCODE 34
00042 
00043 extern uint8_t ff_h261_rl_table_store[2][2*MAX_RUN + MAX_LEVEL + 3];
00044 
00045 static VLC h261_mba_vlc;
00046 static VLC h261_mtype_vlc;
00047 static VLC h261_mv_vlc;
00048 static VLC h261_cbp_vlc;
00049 
00050 static int h261_decode_block(H261Context * h, DCTELEM * block, int n, int coded);
00051 
00052 static av_cold void h261_decode_init_vlc(H261Context *h){
00053     static int done = 0;
00054 
00055     if(!done){
00056         done = 1;
00057         INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
00058                  h261_mba_bits, 1, 1,
00059                  h261_mba_code, 1, 1, 662);
00060         INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
00061                  h261_mtype_bits, 1, 1,
00062                  h261_mtype_code, 1, 1, 80);
00063         INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
00064                  &h261_mv_tab[0][1], 2, 1,
00065                  &h261_mv_tab[0][0], 2, 1, 144);
00066         INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
00067                  &h261_cbp_tab[0][1], 2, 1,
00068                  &h261_cbp_tab[0][0], 2, 1, 512);
00069         ff_init_rl(&h261_rl_tcoeff, ff_h261_rl_table_store);
00070         INIT_VLC_RL(h261_rl_tcoeff, 552);
00071     }
00072 }
00073 
00074 static av_cold int h261_decode_init(AVCodecContext *avctx){
00075     H261Context *h= avctx->priv_data;
00076     MpegEncContext * const s = &h->s;
00077 
00078     // set defaults
00079     MPV_decode_defaults(s);
00080     s->avctx = avctx;
00081 
00082     s->width  = s->avctx->coded_width;
00083     s->height = s->avctx->coded_height;
00084     s->codec_id = s->avctx->codec->id;
00085 
00086     s->out_format = FMT_H261;
00087     s->low_delay= 1;
00088     avctx->pix_fmt= PIX_FMT_YUV420P;
00089 
00090     s->codec_id= avctx->codec->id;
00091 
00092     h261_decode_init_vlc(h);
00093 
00094     h->gob_start_code_skipped = 0;
00095 
00096     return 0;
00097 }
00098 
00103 static int h261_decode_gob_header(H261Context *h){
00104     unsigned int val;
00105     MpegEncContext * const s = &h->s;
00106 
00107     if ( !h->gob_start_code_skipped ){
00108         /* Check for GOB Start Code */
00109         val = show_bits(&s->gb, 15);
00110         if(val)
00111             return -1;
00112 
00113         /* We have a GBSC */
00114         skip_bits(&s->gb, 16);
00115     }
00116 
00117     h->gob_start_code_skipped = 0;
00118 
00119     h->gob_number = get_bits(&s->gb, 4); /* GN */
00120     s->qscale = get_bits(&s->gb, 5); /* GQUANT */
00121 
00122     /* Check if gob_number is valid */
00123     if (s->mb_height==18){ //cif
00124         if ((h->gob_number<=0) || (h->gob_number>12))
00125             return -1;
00126     }
00127     else{ //qcif
00128         if ((h->gob_number!=1) && (h->gob_number!=3) && (h->gob_number!=5))
00129             return -1;
00130     }
00131 
00132     /* GEI */
00133     while (get_bits1(&s->gb) != 0) {
00134         skip_bits(&s->gb, 8);
00135     }
00136 
00137     if(s->qscale==0) {
00138         av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
00139         if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))
00140             return -1;
00141     }
00142 
00143     // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
00144     // subsequent macroblocks, MBA is the difference between the absolute addresses of
00145     // the macroblock and the last transmitted macroblock.
00146     h->current_mba = 0;
00147     h->mba_diff = 0;
00148 
00149     return 0;
00150 }
00151 
00156 static int ff_h261_resync(H261Context *h){
00157     MpegEncContext * const s = &h->s;
00158     int left, ret;
00159 
00160     if ( h->gob_start_code_skipped ){
00161         ret= h261_decode_gob_header(h);
00162         if(ret>=0)
00163             return 0;
00164     }
00165     else{
00166         if(show_bits(&s->gb, 15)==0){
00167             ret= h261_decode_gob_header(h);
00168             if(ret>=0)
00169                 return 0;
00170         }
00171         //OK, it is not where it is supposed to be ...
00172         s->gb= s->last_resync_gb;
00173         align_get_bits(&s->gb);
00174         left= get_bits_left(&s->gb);
00175 
00176         for(;left>15+1+4+5; left-=8){
00177             if(show_bits(&s->gb, 15)==0){
00178                 GetBitContext bak= s->gb;
00179 
00180                 ret= h261_decode_gob_header(h);
00181                 if(ret>=0)
00182                     return 0;
00183 
00184                 s->gb= bak;
00185             }
00186             skip_bits(&s->gb, 8);
00187         }
00188     }
00189 
00190     return -1;
00191 }
00192 
00197 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
00198 {
00199     MpegEncContext * const s = &h->s;
00200     int i;
00201 
00202     s->mb_intra = 0;
00203 
00204     for(i=mba1; i<mba2; i++){
00205         int j, xy;
00206 
00207         s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
00208         s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
00209         xy = s->mb_x + s->mb_y * s->mb_stride;
00210         ff_init_block_index(s);
00211         ff_update_block_index(s);
00212 
00213         for(j=0;j<6;j++)
00214             s->block_last_index[j] = -1;
00215 
00216         s->mv_dir = MV_DIR_FORWARD;
00217         s->mv_type = MV_TYPE_16X16;
00218         s->current_picture.f.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
00219         s->mv[0][0][0] = 0;
00220         s->mv[0][0][1] = 0;
00221         s->mb_skipped = 1;
00222         h->mtype &= ~MB_TYPE_H261_FIL;
00223 
00224         MPV_decode_mb(s, s->block);
00225     }
00226 
00227     return 0;
00228 }
00229 
00230 static int decode_mv_component(GetBitContext *gb, int v){
00231     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
00232 
00233     /* check if mv_diff is valid */
00234     if ( mv_diff < 0 )
00235         return v;
00236 
00237     mv_diff = mvmap[mv_diff];
00238 
00239     if(mv_diff && !get_bits1(gb))
00240         mv_diff= -mv_diff;
00241 
00242     v += mv_diff;
00243     if     (v <=-16) v+= 32;
00244     else if(v >= 16) v-= 32;
00245 
00246     return v;
00247 }
00248 
00249 static int h261_decode_mb(H261Context *h){
00250     MpegEncContext * const s = &h->s;
00251     int i, cbp, xy;
00252 
00253     cbp = 63;
00254     // Read mba
00255     do{
00256         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);
00257 
00258         /* Check for slice end */
00259         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
00260         if (h->mba_diff == MBA_STARTCODE){ // start code
00261             h->gob_start_code_skipped = 1;
00262             return SLICE_END;
00263         }
00264     }
00265     while( h->mba_diff == MBA_STUFFING ); // stuffing
00266 
00267     if ( h->mba_diff < 0 ){
00268         if (get_bits_left(&s->gb) <= 7)
00269             return SLICE_END;
00270 
00271         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
00272         return SLICE_ERROR;
00273     }
00274 
00275     h->mba_diff += 1;
00276     h->current_mba += h->mba_diff;
00277 
00278     if ( h->current_mba > MBA_STUFFING )
00279         return SLICE_ERROR;
00280 
00281     s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
00282     s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
00283     xy = s->mb_x + s->mb_y * s->mb_stride;
00284     ff_init_block_index(s);
00285     ff_update_block_index(s);
00286 
00287     // Read mtype
00288     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
00289     if (h->mtype < 0) {
00290         av_log(s->avctx, AV_LOG_ERROR, "illegal mtype %d\n", h->mtype);
00291         return SLICE_ERROR;
00292     }
00293     h->mtype = h261_mtype_map[h->mtype];
00294 
00295     // Read mquant
00296     if ( IS_QUANT ( h->mtype ) ){
00297         ff_set_qscale(s, get_bits(&s->gb, 5));
00298     }
00299 
00300     s->mb_intra = IS_INTRA4x4(h->mtype);
00301 
00302     // Read mv
00303     if ( IS_16X16 ( h->mtype ) ){
00304         // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
00305         // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
00306         // following three situations:
00307         // 1) evaluating MVD for macroblocks 1, 12 and 23;
00308         // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
00309         // 3) MTYPE of the previous macroblock was not MC.
00310         if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
00311              ( h->mba_diff != 1))
00312         {
00313             h->current_mv_x = 0;
00314             h->current_mv_y = 0;
00315         }
00316 
00317         h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
00318         h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
00319     }else{
00320         h->current_mv_x = 0;
00321         h->current_mv_y = 0;
00322     }
00323 
00324     // Read cbp
00325     if ( HAS_CBP( h->mtype ) ){
00326         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
00327     }
00328 
00329     if(s->mb_intra){
00330         s->current_picture.f.mb_type[xy] = MB_TYPE_INTRA;
00331         goto intra;
00332     }
00333 
00334     //set motion vectors
00335     s->mv_dir = MV_DIR_FORWARD;
00336     s->mv_type = MV_TYPE_16X16;
00337     s->current_picture.f.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;
00338     s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
00339     s->mv[0][0][1] = h->current_mv_y * 2;
00340 
00341 intra:
00342     /* decode each block */
00343     if(s->mb_intra || HAS_CBP(h->mtype)){
00344         s->dsp.clear_blocks(s->block[0]);
00345         for (i = 0; i < 6; i++) {
00346             if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
00347                 return SLICE_ERROR;
00348             }
00349             cbp+=cbp;
00350         }
00351     }else{
00352         for (i = 0; i < 6; i++)
00353             s->block_last_index[i]= -1;
00354     }
00355 
00356     MPV_decode_mb(s, s->block);
00357 
00358     return SLICE_OK;
00359 }
00360 
00365 static int h261_decode_block(H261Context * h, DCTELEM * block,
00366                              int n, int coded)
00367 {
00368     MpegEncContext * const s = &h->s;
00369     int code, level, i, j, run;
00370     RLTable *rl = &h261_rl_tcoeff;
00371     const uint8_t *scan_table;
00372 
00373     // For the variable length encoding there are two code tables, one being used for
00374     // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
00375     // for all other LEVELs except the first one in INTRA blocks which is fixed length
00376     // coded with 8 bits.
00377     // NOTE: the two code tables only differ in one VLC so we handle that manually.
00378     scan_table = s->intra_scantable.permutated;
00379     if (s->mb_intra){
00380         /* DC coef */
00381         level = get_bits(&s->gb, 8);
00382         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
00383         if((level&0x7F) == 0){
00384             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
00385             return -1;
00386         }
00387         // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
00388         if (level == 255)
00389             level = 128;
00390         block[0] = level;
00391         i = 1;
00392     }else if(coded){
00393         // Run  Level   Code
00394         // EOB                  Not possible for first level when cbp is available (that's why the table is different)
00395         // 0    1               1s
00396         // *    *               0*
00397         int check = show_bits(&s->gb, 2);
00398         i = 0;
00399         if ( check & 0x2 ){
00400             skip_bits(&s->gb, 2);
00401             block[0] = ( check & 0x1 ) ? -1 : 1;
00402             i = 1;
00403         }
00404     }else{
00405         i = 0;
00406     }
00407     if(!coded){
00408         s->block_last_index[n] = i - 1;
00409         return 0;
00410     }
00411     for(;;){
00412         code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
00413         if (code < 0){
00414             av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
00415             return -1;
00416         }
00417         if (code == rl->n) {
00418             /* escape */
00419             // 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.
00420             run = get_bits(&s->gb, 6);
00421             level = get_sbits(&s->gb, 8);
00422         }else if(code == 0){
00423             break;
00424         }else{
00425             run = rl->table_run[code];
00426             level = rl->table_level[code];
00427             if (get_bits1(&s->gb))
00428                 level = -level;
00429         }
00430         i += run;
00431         if (i >= 64){
00432             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
00433             return -1;
00434         }
00435         j = scan_table[i];
00436         block[j] = level;
00437         i++;
00438     }
00439     s->block_last_index[n] = i-1;
00440     return 0;
00441 }
00442 
00447 static int h261_decode_picture_header(H261Context *h){
00448     MpegEncContext * const s = &h->s;
00449     int format, i;
00450     uint32_t startcode= 0;
00451 
00452     for(i= get_bits_left(&s->gb); i>24; i-=1){
00453         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
00454 
00455         if(startcode == 0x10)
00456             break;
00457     }
00458 
00459     if (startcode != 0x10){
00460         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
00461         return -1;
00462     }
00463 
00464     /* temporal reference */
00465     i= get_bits(&s->gb, 5); /* picture timestamp */
00466     if(i < (s->picture_number&31))
00467         i += 32;
00468     s->picture_number = (s->picture_number&~31) + i;
00469 
00470     s->avctx->time_base= (AVRational){1001, 30000};
00471     s->current_picture.f.pts = s->picture_number;
00472 
00473 
00474     /* PTYPE starts here */
00475     skip_bits1(&s->gb); /* split screen off */
00476     skip_bits1(&s->gb); /* camera  off */
00477     skip_bits1(&s->gb); /* freeze picture release off */
00478 
00479     format = get_bits1(&s->gb);
00480 
00481     //only 2 formats possible
00482     if (format == 0){//QCIF
00483         s->width = 176;
00484         s->height = 144;
00485         s->mb_width = 11;
00486         s->mb_height = 9;
00487     }else{//CIF
00488         s->width = 352;
00489         s->height = 288;
00490         s->mb_width = 22;
00491         s->mb_height = 18;
00492     }
00493 
00494     s->mb_num = s->mb_width * s->mb_height;
00495 
00496     skip_bits1(&s->gb); /* still image mode off */
00497     skip_bits1(&s->gb); /* Reserved */
00498 
00499     /* PEI */
00500     while (get_bits1(&s->gb) != 0){
00501         skip_bits(&s->gb, 8);
00502     }
00503 
00504     // h261 has no I-FRAMES, but if we pass AV_PICTURE_TYPE_I for the first frame, the codec crashes if it does
00505     // not contain all I-blocks (e.g. when a packet is lost)
00506     s->pict_type = AV_PICTURE_TYPE_P;
00507 
00508     h->gob_number = 0;
00509     return 0;
00510 }
00511 
00512 static int h261_decode_gob(H261Context *h){
00513     MpegEncContext * const s = &h->s;
00514 
00515     ff_set_qscale(s, s->qscale);
00516 
00517     /* decode mb's */
00518     while(h->current_mba <= MBA_STUFFING)
00519     {
00520         int ret;
00521         /* DCT & quantize */
00522         ret= h261_decode_mb(h);
00523         if(ret<0){
00524             if(ret==SLICE_END){
00525                 h261_decode_mb_skipped(h, h->current_mba, 33);
00526                 return 0;
00527             }
00528             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
00529             return -1;
00530         }
00531 
00532         h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
00533     }
00534 
00535     return -1;
00536 }
00537 
00541 static int get_consumed_bytes(MpegEncContext *s, int buf_size){
00542     int pos= get_bits_count(&s->gb)>>3;
00543     if(pos==0) pos=1; //avoid infinite loops (i doubt that is needed but ...)
00544     if(pos+10>buf_size) pos=buf_size; // oops ;)
00545 
00546     return pos;
00547 }
00548 
00549 static int h261_decode_frame(AVCodecContext *avctx,
00550                              void *data, int *data_size,
00551                              AVPacket *avpkt)
00552 {
00553     const uint8_t *buf = avpkt->data;
00554     int buf_size = avpkt->size;
00555     H261Context *h= avctx->priv_data;
00556     MpegEncContext *s = &h->s;
00557     int ret;
00558     AVFrame *pict = data;
00559 
00560     av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
00561     av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
00562     s->flags= avctx->flags;
00563     s->flags2= avctx->flags2;
00564 
00565     h->gob_start_code_skipped=0;
00566 
00567 retry:
00568 
00569     init_get_bits(&s->gb, buf, buf_size*8);
00570 
00571     if(!s->context_initialized){
00572         if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
00573             return -1;
00574     }
00575 
00576     //we need to set current_picture_ptr before reading the header, otherwise we cannot store anyting im there
00577     if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
00578         int i= ff_find_unused_picture(s, 0);
00579         if (i < 0)
00580             return i;
00581         s->current_picture_ptr= &s->picture[i];
00582     }
00583 
00584     ret = h261_decode_picture_header(h);
00585 
00586     /* skip if the header was thrashed */
00587     if (ret < 0){
00588         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
00589         return -1;
00590     }
00591 
00592     if (s->width != avctx->coded_width || s->height != avctx->coded_height){
00593         ParseContext pc= s->parse_context; //FIXME move this demuxing hack to libavformat
00594         s->parse_context.buffer=0;
00595         MPV_common_end(s);
00596         s->parse_context= pc;
00597     }
00598     if (!s->context_initialized) {
00599         avcodec_set_dimensions(avctx, s->width, s->height);
00600 
00601         goto retry;
00602     }
00603 
00604     // for skipping the frame
00605     s->current_picture.f.pict_type = s->pict_type;
00606     s->current_picture.f.key_frame = s->pict_type == AV_PICTURE_TYPE_I;
00607 
00608     if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==AV_PICTURE_TYPE_B)
00609        ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=AV_PICTURE_TYPE_I)
00610        || avctx->skip_frame >= AVDISCARD_ALL)
00611         return get_consumed_bytes(s, buf_size);
00612 
00613     if(MPV_frame_start(s, avctx) < 0)
00614         return -1;
00615 
00616     ff_er_frame_start(s);
00617 
00618     /* decode each macroblock */
00619     s->mb_x=0;
00620     s->mb_y=0;
00621 
00622     while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
00623         if(ff_h261_resync(h)<0)
00624             break;
00625         h261_decode_gob(h);
00626     }
00627     MPV_frame_end(s);
00628 
00629 assert(s->current_picture.f.pict_type == s->current_picture_ptr->f.pict_type);
00630 assert(s->current_picture.f.pict_type == s->pict_type);
00631     *pict= *(AVFrame*)s->current_picture_ptr;
00632     ff_print_debug_info(s, pict);
00633 
00634     *data_size = sizeof(AVFrame);
00635 
00636     return get_consumed_bytes(s, buf_size);
00637 }
00638 
00639 static av_cold int h261_decode_end(AVCodecContext *avctx)
00640 {
00641     H261Context *h= avctx->priv_data;
00642     MpegEncContext *s = &h->s;
00643 
00644     MPV_common_end(s);
00645     return 0;
00646 }
00647 
00648 AVCodec ff_h261_decoder = {
00649     .name           = "h261",
00650     .type           = AVMEDIA_TYPE_VIDEO,
00651     .id             = CODEC_ID_H261,
00652     .priv_data_size = sizeof(H261Context),
00653     .init           = h261_decode_init,
00654     .close          = h261_decode_end,
00655     .decode         = h261_decode_frame,
00656     .capabilities   = CODEC_CAP_DR1,
00657     .max_lowres = 3,
00658     .long_name = NULL_IF_CONFIG_SMALL("H.261"),
00659 };
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