aboutsummaryrefslogtreecommitdiffstats
path: root/libavcodec/h261.c
blob: 8b73f387c42474260116ed571512d4860b7dbb47 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
/*
 * H261 decoder
 * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
 * Copyright (c) 2004 Maarten Daniels
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/**
 * @file h261.c
 * h261codec.
 */

#include "common.h"
#include "dsputil.h"
#include "avcodec.h"
#include "mpegvideo.h"
#include "h261data.h"


#define H261_MBA_VLC_BITS 9
#define H261_MTYPE_VLC_BITS 6
#define H261_MV_VLC_BITS 7
#define H261_CBP_VLC_BITS 9
#define TCOEFF_VLC_BITS 9

#define MBA_STUFFING 33
#define MBA_STARTCODE 34
#define IS_FIL(a)    ((a)&MB_TYPE_H261_FIL)

/**
 * H261Context
 */
typedef struct H261Context{
    MpegEncContext s;

    int current_mba;
    int previous_mba;
    int mba_diff;
    int mtype;
    int current_mv_x;
    int current_mv_y;
    int gob_number;
    int bits_left; //8 - nr of bits left of the following frame in the last byte in this frame
    int last_bits; //bits left of the following frame in the last byte in this frame
    int gob_start_code_skipped; // 1 if gob start code is already read before gob header is read
}H261Context;

void ff_h261_loop_filter(MpegEncContext *s){
    H261Context * h= (H261Context*)s;
    const int linesize  = s->linesize;
    const int uvlinesize= s->uvlinesize;
    uint8_t *dest_y = s->dest[0];
    uint8_t *dest_cb= s->dest[1];
    uint8_t *dest_cr= s->dest[2];

    if(!(IS_FIL (h->mtype)))
        return;

    s->dsp.h261_loop_filter(dest_y                   , linesize);
    s->dsp.h261_loop_filter(dest_y                + 8, linesize);
    s->dsp.h261_loop_filter(dest_y + 8 * linesize    , linesize);
    s->dsp.h261_loop_filter(dest_y + 8 * linesize + 8, linesize);
    s->dsp.h261_loop_filter(dest_cb, uvlinesize);
    s->dsp.h261_loop_filter(dest_cr, uvlinesize);
}

static int ff_h261_get_picture_format(int width, int height){
    // QCIF
    if (width == 176 && height == 144)
        return 0;
    // CIF
    else if (width == 352 && height == 288)
        return 1;
    // ERROR
    else
        return -1;
}

static void h261_encode_block(H261Context * h, DCTELEM * block,
                              int n);
static int h261_decode_block(H261Context *h, DCTELEM *block,
                             int n, int coded);

void ff_h261_encode_picture_header(MpegEncContext * s, int picture_number){
    H261Context * h = (H261Context *) s;
    int format, temp_ref;

    align_put_bits(&s->pb);

    /* Update the pointer to last GOB */
    s->ptr_lastgob = pbBufPtr(&s->pb);

    put_bits(&s->pb, 20, 0x10); /* PSC */

    temp_ref= s->picture_number * (int64_t)30000 * s->avctx->frame_rate_base / 
                         (1001 * (int64_t)s->avctx->frame_rate);
    put_bits(&s->pb, 5, temp_ref & 0x1f); /* TemporalReference */

    put_bits(&s->pb, 1, 0); /* split screen off */
    put_bits(&s->pb, 1, 0); /* camera  off */
    put_bits(&s->pb, 1, 0); /* freeze picture release off */
    
    format = ff_h261_get_picture_format(s->width, s->height);
    
    put_bits(&s->pb, 1, format); /* 0 == QCIF, 1 == CIF */

    put_bits(&s->pb, 1, 0); /* still image mode */
    put_bits(&s->pb, 1, 0); /* reserved */

    put_bits(&s->pb, 1, 0); /* no PEI */    
    if(format == 0)
        h->gob_number = -1;
    else
        h->gob_number = 0;
    h->current_mba = 0;
}

/**
 * Encodes a group of blocks header.
 */
static void h261_encode_gob_header(MpegEncContext * s, int mb_line){
    H261Context * h = (H261Context *)s;
    if(ff_h261_get_picture_format(s->width, s->height) == 0){
        h->gob_number+=2; // QCIF
    }
    else{
        h->gob_number++; // CIF
    }
    put_bits(&s->pb, 16, 1); /* GBSC */
    put_bits(&s->pb, 4, h->gob_number); /* GN */
    put_bits(&s->pb, 5, s->qscale); /* GQUANT */
    put_bits(&s->pb, 1, 0); /* no GEI */
    h->current_mba = 0;
    h->previous_mba = 0;
    h->current_mv_x=0;
    h->current_mv_y=0;
}

void ff_h261_reorder_mb_index(MpegEncContext* s){
    int index= s->mb_x + s->mb_y*s->mb_width;

    if(index % 33 == 0)
        h261_encode_gob_header(s,0);

    /* for CIF the GOB's are fragmented in the middle of a scanline
       that's why we need to adjust the x and y index of the macroblocks */
    if(ff_h261_get_picture_format(s->width,s->height) == 1){ // CIF
        s->mb_x =     index % 11 ; index /= 11;
        s->mb_y =     index %  3 ; index /=  3;
        s->mb_x+= 11*(index %  2); index /=  2;
        s->mb_y+=  3*index;
        
        ff_init_block_index(s);
        ff_update_block_index(s);
    }
}

static void h261_encode_motion(H261Context * h, int val){
    MpegEncContext * const s = &h->s;
    int sign, code;
    if(val==0){
        code = 0;
        put_bits(&s->pb,h261_mv_tab[code][1],h261_mv_tab[code][0]);
    } 
    else{
        if(val > 16)
            val -=32;
        if(val < -16)
            val+=32;
        sign = val < 0;
        code = sign ? -val : val; 
        put_bits(&s->pb,h261_mv_tab[code][1],h261_mv_tab[code][0]);
        put_bits(&s->pb,1,sign);
    }
}

static inline int get_cbp(MpegEncContext * s,
                      DCTELEM block[6][64])
{
    int i, cbp;
    cbp= 0;
    for (i = 0; i < 6; i++) {
        if (s->block_last_index[i] >= 0)
            cbp |= 1 << (5 - i);
    }
    return cbp;
}
void ff_h261_encode_mb(MpegEncContext * s,
         DCTELEM block[6][64],
         int motion_x, int motion_y)
{
    H261Context * h = (H261Context *)s;
    int mvd, mv_diff_x, mv_diff_y, i, cbp;
    cbp = 63; // avoid warning
    mvd = 0;
 
    h->current_mba++;
    h->mtype = 0;
 
    if (!s->mb_intra){
        /* compute cbp */
        cbp= get_cbp(s, block);
   
        /* mvd indicates if this block is motion compensated */
        mvd = motion_x | motion_y;

        if((cbp | mvd | s->dquant ) == 0) {
            /* skip macroblock */
            s->skip_count++;
            h->current_mv_x=0;
            h->current_mv_y=0;
            return;
        }
    }

    /* MB is not skipped, encode MBA */
    put_bits(&s->pb, h261_mba_bits[(h->current_mba-h->previous_mba)-1], h261_mba_code[(h->current_mba-h->previous_mba)-1]);
 
    /* calculate MTYPE */
    if(!s->mb_intra){
        h->mtype++;
        
        if(mvd || s->loop_filter)
            h->mtype+=3;
        if(s->loop_filter)
            h->mtype+=3;
        if(cbp || s->dquant)
            h->mtype++;
        assert(h->mtype > 1);
    }

    if(s->dquant) 
        h->mtype++;

    put_bits(&s->pb, h261_mtype_bits[h->mtype], h261_mtype_code[h->mtype]);
 
    h->mtype = h261_mtype_map[h->mtype];
 
    if(IS_QUANT(h->mtype)){
        ff_set_qscale(s,s->qscale+s->dquant);
        put_bits(&s->pb, 5, s->qscale);
    }
 
    if(IS_16X16(h->mtype)){
        mv_diff_x = (motion_x >> 1) - h->current_mv_x;
        mv_diff_y = (motion_y >> 1) - h->current_mv_y;
        h->current_mv_x = (motion_x >> 1);
        h->current_mv_y = (motion_y >> 1);
        h261_encode_motion(h,mv_diff_x);
        h261_encode_motion(h,mv_diff_y);
    }
 
    h->previous_mba = h->current_mba;
 
    if(HAS_CBP(h->mtype)){
        put_bits(&s->pb,h261_cbp_tab[cbp-1][1],h261_cbp_tab[cbp-1][0]); 
    }
    for(i=0; i<6; i++) {
        /* encode each block */
        h261_encode_block(h, block[i], i);
    }

    if ( ( h->current_mba == 11 ) || ( h->current_mba == 22 ) || ( h->current_mba == 33 ) || ( !IS_16X16 ( h->mtype ) )){
        h->current_mv_x=0;
        h->current_mv_y=0;
    }
}

void ff_h261_encode_init(MpegEncContext *s){
    static int done = 0;
    
    if (!done) {
        done = 1;
        init_rl(&h261_rl_tcoeff);
    }

    s->min_qcoeff= -127;
    s->max_qcoeff=  127;
    s->y_dc_scale_table=
    s->c_dc_scale_table= ff_mpeg1_dc_scale_table;
}


/**
 * encodes a 8x8 block.
 * @param block the 8x8 block
 * @param n block index (0-3 are luma, 4-5 are chroma)
 */
static void h261_encode_block(H261Context * h, DCTELEM * block, int n){
    MpegEncContext * const s = &h->s;
    int level, run, last, i, j, last_index, last_non_zero, sign, slevel, code;
    RLTable *rl;

    rl = &h261_rl_tcoeff;
    if (s->mb_intra) {
        /* DC coef */
        level = block[0];
        /* 255 cannot be represented, so we clamp */
        if (level > 254) {
            level = 254;
            block[0] = 254;
        }
        /* 0 cannot be represented also */
        else if (level < 1) {
            level = 1;
            block[0] = 1;
        }
        if (level == 128)
            put_bits(&s->pb, 8, 0xff);
        else
            put_bits(&s->pb, 8, level);
        i = 1;
    } else if((block[0]==1 || block[0] == -1) && (s->block_last_index[n] > -1)){
        //special case
        put_bits(&s->pb,1,1);
        put_bits(&s->pb,1,block[0]>0 ? 0 : 1 );
        i = 1;
    } else {
        i = 0;
    }
   
    /* AC coefs */
    last_index = s->block_last_index[n];
    last_non_zero = i - 1;
    for (; i <= last_index; i++) {
        j = s->intra_scantable.permutated[i];
        level = block[j];
        if (level) {
            run = i - last_non_zero - 1;
            last = (i == last_index);
            sign = 0;
            slevel = level;
            if (level < 0) {
                sign = 1;
                level = -level;
            }
            code = get_rl_index(rl, 0 /*no last in H.261, EOB is used*/, run, level);
            if(run==0 && level < 16)
            code+=1;
            put_bits(&s->pb, rl->table_vlc[code][1], rl->table_vlc[code][0]);
            if (code == rl->n) {
                put_bits(&s->pb, 6, run);
                assert(slevel != 0);
                if(slevel < -127){
                    slevel = -127;
                }
                else if(slevel > 127){
                    slevel = 127;
                }
                put_bits(&s->pb, 8, slevel & 0xff);
            } else {
                put_bits(&s->pb, 1, sign);
            }
            last_non_zero = i;
        }
    }
    if(last_index > -1){
        put_bits(&s->pb, rl->table_vlc[0][1], rl->table_vlc[0][0]);// END OF BLOCK
    }
}

/***********************************************/
/* decoding */

static VLC h261_mba_vlc;
static VLC h261_mtype_vlc;
static VLC h261_mv_vlc;
static VLC h261_cbp_vlc;

void init_vlc_rl(RLTable *rl);

static void h261_decode_init_vlc(H261Context *h){
    static int done = 0;

    if(!done){
        done = 1;
        init_vlc(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
                 h261_mba_bits, 1, 1,
                 h261_mba_code, 1, 1);
        init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
                 h261_mtype_bits, 1, 1,
                 h261_mtype_code, 1, 1);
        init_vlc(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
                 &h261_mv_tab[0][1], 2, 1,
                 &h261_mv_tab[0][0], 2, 1);
        init_vlc(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
                 &h261_cbp_tab[0][1], 2, 1,
                 &h261_cbp_tab[0][0], 2, 1);
        init_rl(&h261_rl_tcoeff);
        init_vlc_rl(&h261_rl_tcoeff);
    }
}

static int h261_decode_init(AVCodecContext *avctx){
    H261Context *h= avctx->priv_data;
    MpegEncContext * const s = &h->s;

    // set defaults
    MPV_decode_defaults(s);
    s->avctx = avctx;

    s->width  = s->avctx->coded_width;
    s->height = s->avctx->coded_height;
    s->codec_id = s->avctx->codec->id;

    s->out_format = FMT_H261;
    s->low_delay= 1;
    avctx->pix_fmt= PIX_FMT_YUV420P;

    s->codec_id= avctx->codec->id;

    h261_decode_init_vlc(h);

    h->gob_start_code_skipped = 0;
    
    return 0;
}

/**
 * decodes the group of blocks header or slice header.
 * @return <0 if an error occured
 */
static int h261_decode_gob_header(H261Context *h){
    unsigned int val;
    MpegEncContext * const s = &h->s;
    
    if ( !h->gob_start_code_skipped ){
        /* Check for GOB Start Code */
        val = show_bits(&s->gb, 15);
        if(val)
            return -1;

        /* We have a GBSC */
        skip_bits(&s->gb, 16);
    }

    h->gob_start_code_skipped = 0;

    h->gob_number = get_bits(&s->gb, 4); /* GN */
    s->qscale = get_bits(&s->gb, 5); /* GQUANT */

    /* Check if gob_number is valid */
    if (s->mb_height==18){ //cif
        if ((h->gob_number<=0) || (h->gob_number>12))
            return -1;
    }
    else{ //qcif
        if ((h->gob_number!=1) && (h->gob_number!=3) && (h->gob_number!=5))
            return -1;
    }

    /* GEI */
    while (get_bits1(&s->gb) != 0) {
        skip_bits(&s->gb, 8);
    }

    if(s->qscale==0)
        return -1;

    // For the first transmitted macroblock in a GOB, MBA is the absolute address. For
    // subsequent macroblocks, MBA is the difference between the absolute addresses of
    // the macroblock and the last transmitted macroblock.
    h->current_mba = 0;
    h->mba_diff = 0;

    return 0;
}

/**
 * decodes the group of blocks / video packet header.
 * @return <0 if no resync found
 */
static int ff_h261_resync(H261Context *h){
    MpegEncContext * const s = &h->s;
    int left, ret;

    if ( h->gob_start_code_skipped ){
        ret= h261_decode_gob_header(h);
        if(ret>=0)
            return 0;
    }
    else{
        if(show_bits(&s->gb, 15)==0){
            ret= h261_decode_gob_header(h);
            if(ret>=0)
                return 0;
        }
        //ok, its not where its supposed to be ...
        s->gb= s->last_resync_gb;
        align_get_bits(&s->gb);
        left= s->gb.size_in_bits - get_bits_count(&s->gb);

        for(;left>15+1+4+5; left-=8){
            if(show_bits(&s->gb, 15)==0){
                GetBitContext bak= s->gb;

                ret= h261_decode_gob_header(h);
                if(ret>=0)
                    return 0;

                s->gb= bak;
            }
            skip_bits(&s->gb, 8);
        }
    }

    return -1;
}

/**
 * decodes skipped macroblocks
 * @return 0
 */
static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2 )
{
    MpegEncContext * const s = &h->s;
    int i;
    
    s->mb_intra = 0;

    for(i=mba1; i<mba2; i++){
        int j, xy;

        s->mb_x= ((h->gob_number-1) % 2) * 11 + i % 11;
        s->mb_y= ((h->gob_number-1) / 2) * 3 + i / 11;
        xy = s->mb_x + s->mb_y * s->mb_stride;
        ff_init_block_index(s);
        ff_update_block_index(s);
        s->dsp.clear_blocks(s->block[0]);

        for(j=0;j<6;j++)
            s->block_last_index[j] = -1;

        s->mv_dir = MV_DIR_FORWARD;
        s->mv_type = MV_TYPE_16X16;
        s->current_picture.mb_type[xy]= MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
        s->mv[0][0][0] = 0;
        s->mv[0][0][1] = 0;
        s->mb_skiped = 1;
        h->mtype &= ~MB_TYPE_H261_FIL;

        MPV_decode_mb(s, s->block);
    }

    return 0;
}

static int decode_mv_component(GetBitContext *gb, int v){
    int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);

    /* check if mv_diff is valid */
    if ( mv_diff < 0 )
        return v;

    mv_diff = mvmap[mv_diff];

    if(mv_diff && !get_bits1(gb))
        mv_diff= -mv_diff;
    
    v += mv_diff;
    if     (v <=-16) v+= 32;
    else if(v >= 16) v-= 32;

    return v;
}

static int h261_decode_mb(H261Context *h){
    MpegEncContext * const s = &h->s;
    int i, cbp, xy;

    cbp = 63;
    // Read mba
    do{
        h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table, H261_MBA_VLC_BITS, 2);

        /* Check for slice end */
        /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
        if (h->mba_diff == MBA_STARTCODE){ // start code
            h->gob_start_code_skipped = 1;
            return SLICE_END;
        }
    }
    while( h->mba_diff == MBA_STUFFING ); // stuffing

    if ( h->mba_diff < 0 ){
        if ( get_bits_count(&s->gb) + 7 >= s->gb.size_in_bits )
            return SLICE_END;

        av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
        return SLICE_ERROR;
    }

    h->mba_diff += 1;
    h->current_mba += h->mba_diff;

    if ( h->current_mba > MBA_STUFFING )
        return SLICE_ERROR;
    
    s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1) % 11);
    s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1) / 11);
    xy = s->mb_x + s->mb_y * s->mb_stride;
    ff_init_block_index(s);
    ff_update_block_index(s);
    s->dsp.clear_blocks(s->block[0]);

    // Read mtype
    h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
    h->mtype = h261_mtype_map[h->mtype];

    // Read mquant
    if ( IS_QUANT ( h->mtype ) ){
        ff_set_qscale(s, get_bits(&s->gb, 5));
    }

    s->mb_intra = IS_INTRA4x4(h->mtype);

    // Read mv
    if ( IS_16X16 ( h->mtype ) ){
        // Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
        // vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
        // following three situations:
        // 1) evaluating MVD for macroblocks 1, 12 and 23;
        // 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
        // 3) MTYPE of the previous macroblock was not MC.
        if ( ( h->current_mba == 1 ) || ( h->current_mba == 12 ) || ( h->current_mba == 23 ) ||
             ( h->mba_diff != 1))
        {
            h->current_mv_x = 0;
            h->current_mv_y = 0;
        }

        h->current_mv_x= decode_mv_component(&s->gb, h->current_mv_x);
        h->current_mv_y= decode_mv_component(&s->gb, h->current_mv_y);
    }else{
        h->current_mv_x = 0;
        h->current_mv_y = 0;
    }

    // Read cbp
    if ( HAS_CBP( h->mtype ) ){
        cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
    }

    if(s->mb_intra){
        s->current_picture.mb_type[xy]= MB_TYPE_INTRA;
        goto intra;
    }

    //set motion vectors
    s->mv_dir = MV_DIR_FORWARD;
    s->mv_type = MV_TYPE_16X16;
    s->current_picture.mb_type[xy]= MB_TYPE_16x16 | MB_TYPE_L0;
    s->mv[0][0][0] = h->current_mv_x * 2;//gets divided by 2 in motion compensation
    s->mv[0][0][1] = h->current_mv_y * 2;

intra:
    /* decode each block */
    if(s->mb_intra || HAS_CBP(h->mtype)){
        for (i = 0; i < 6; i++) {
            if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){
                return SLICE_ERROR;
            }
            cbp+=cbp;
        }
    }

    MPV_decode_mb(s, s->block);

    return SLICE_OK;
}

/**
 * decodes a macroblock
 * @return <0 if an error occured
 */
static int h261_decode_block(H261Context * h, DCTELEM * block,
                             int n, int coded)
{
    MpegEncContext * const s = &h->s;
    int code, level, i, j, run;
    RLTable *rl = &h261_rl_tcoeff;
    const uint8_t *scan_table;
    
    // For the variable length encoding there are two code tables, one being used for
    // the first transmitted LEVEL in INTER, INTER+MC and INTER+MC+FIL blocks, the second
    // for all other LEVELs except the first one in INTRA blocks which is fixed length
    // coded with 8 bits.
    // NOTE: the two code tables only differ in one VLC so we handle that manually.
    scan_table = s->intra_scantable.permutated;
    if (s->mb_intra){
        /* DC coef */
        level = get_bits(&s->gb, 8);
        // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
        if((level&0x7F) == 0){
            av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n", level, s->mb_x, s->mb_y);
            return -1;
        }
        // The code 1000 0000 is not used, the reconstruction level of 1024 being coded as 1111 1111.
        if (level == 255)
            level = 128;
        block[0] = level;
        i = 1;
    }else if(coded){
        // Run  Level   Code
        // EOB                  Not possible for first level when cbp is available (that's why the table is different)
        // 0    1               1s
        // *    *               0*
        int check = show_bits(&s->gb, 2);
        i = 0;
        if ( check & 0x2 ){
            skip_bits(&s->gb, 2);
            block[0] = ( check & 0x1 ) ? -1 : 1;
            i = 1;
        }
    }else{
        i = 0;
    }
    if(!coded){
        s->block_last_index[n] = i - 1;
        return 0;
    }
    for(;;){
        code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
        if (code < 0){
            av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
            return -1;
        }
        if (code == rl->n) {
            /* escape */
            // 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.
            run = get_bits(&s->gb, 6);
            level = (int8_t)get_bits(&s->gb, 8);
        }else if(code == 0){
            break;
        }else{
            run = rl->table_run[code];
            level = rl->table_level[code];
            if (get_bits1(&s->gb))
                level = -level;
        }
        i += run;
        if (i >= 64){
            av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
            return -1;
        }
        j = scan_table[i];
        block[j] = level;
        i++;
    }
    s->block_last_index[n] = i-1;
    return 0;
}

/**
 * decodes the H261 picture header.
 * @return <0 if no startcode found
 */
int h261_decode_picture_header(H261Context *h){
    MpegEncContext * const s = &h->s;
    int format, i;
    uint32_t startcode= 0;

    for(i= s->gb.size_in_bits - get_bits_count(&s->gb); i>24; i-=1){
        startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;

        if(startcode == 0x10)
            break;
    }

    if (startcode != 0x10){
        av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
        return -1;
    }

    /* temporal reference */
    s->picture_number = get_bits(&s->gb, 5); /* picture timestamp */

    /* PTYPE starts here */
    skip_bits1(&s->gb); /* split screen off */
    skip_bits1(&s->gb); /* camera  off */
    skip_bits1(&s->gb); /* freeze picture release off */

    format = get_bits1(&s->gb);

    //only 2 formats possible
    if (format == 0){//QCIF
        s->width = 176;
        s->height = 144;
        s->mb_width = 11;
        s->mb_height = 9;
    }else{//CIF
        s->width = 352;
        s->height = 288;
        s->mb_width = 22;
        s->mb_height = 18;
    }

    s->mb_num = s->mb_width * s->mb_height;

    skip_bits1(&s->gb); /* still image mode off */
    skip_bits1(&s->gb); /* Reserved */

    /* PEI */
    while (get_bits1(&s->gb) != 0){
        skip_bits(&s->gb, 8);
    }

    // h261 has no I-FRAMES, but if we pass I_TYPE for the first frame, the codec crashes if it does 
    // not contain all I-blocks (e.g. when a packet is lost)
    s->pict_type = P_TYPE;

    h->gob_number = 0;
    return 0;
}

static int h261_decode_gob(H261Context *h){
    MpegEncContext * const s = &h->s;
    
    ff_set_qscale(s, s->qscale);

    /* decode mb's */
    while(h->current_mba <= MBA_STUFFING)
    {
        int ret;
        /* DCT & quantize */
        ret= h261_decode_mb(h);
        if(ret<0){
            if(ret==SLICE_END){
                h261_decode_mb_skipped(h, h->current_mba, 33);                
                return 0;
            }
            av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", s->mb_x + s->mb_y*s->mb_stride);
            return -1;
        }
        
        h261_decode_mb_skipped(h, h->current_mba-h->mba_diff, h->current_mba-1);
    }
    
    return -1;
}

static int h261_find_frame_end(ParseContext *pc, AVCodecContext* avctx, const uint8_t *buf, int buf_size){
    int vop_found, i, j, bits_left, last_bits;
    uint32_t state;

    H261Context *h = avctx->priv_data;

    if(h){
        bits_left = h->bits_left;
        last_bits = h->last_bits;
    }
    else{
        bits_left = 0;
        last_bits = 0;
    }

    vop_found= pc->frame_start_found;
    state= pc->state;
    if(bits_left!=0 && !vop_found)
        state = state << (8-bits_left) | last_bits;
    i=0;
    if(!vop_found){
        for(i=0; i<buf_size; i++){
            state= (state<<8) | buf[i];
            for(j=0; j<8; j++){
                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
                    i++;
                    vop_found=1;
                    break;
                }
            }
            if(vop_found)
                    break;    
        }
    }
    if(vop_found){
        for(; i<buf_size; i++){
            if(avctx->flags & CODEC_FLAG_TRUNCATED)//XXX ffplay workaround, someone a better solution?
                state= (state<<8) | buf[i];
            for(j=0; j<8; j++){
                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
                    pc->frame_start_found=0;
                    pc->state=-1;
                    return i-3;
                }
            }
        }
    }

    pc->frame_start_found= vop_found;
    pc->state= state;
    return END_NOT_FOUND;
}

static int h261_parse(AVCodecParserContext *s,
                      AVCodecContext *avctx,
                      uint8_t **poutbuf, int *poutbuf_size, 
                      const uint8_t *buf, int buf_size)
{
    ParseContext *pc = s->priv_data;
    int next;
    
    next= h261_find_frame_end(pc,avctx, buf, buf_size);
    if (ff_combine_frame(pc, next, (uint8_t **)&buf, &buf_size) < 0) {
        *poutbuf = NULL;
        *poutbuf_size = 0;
        return buf_size;
    }
    *poutbuf = (uint8_t *)buf;
    *poutbuf_size = buf_size;
    return next;
}

/**
 * returns the number of bytes consumed for building the current frame
 */
static int get_consumed_bytes(MpegEncContext *s, int buf_size){
    if(s->flags&CODEC_FLAG_TRUNCATED){
        int pos= (get_bits_count(&s->gb)+7)>>3;
        pos -= s->parse_context.last_index;
        if(pos<0) pos=0;// padding is not really read so this might be -1
        return pos;
    }else{
        int pos= get_bits_count(&s->gb)>>3;
        if(pos==0) pos=1; //avoid infinite loops (i doubt thats needed but ...)
        if(pos+10>buf_size) pos=buf_size; // oops ;)

        return pos;
    }
}

static int h261_decode_frame(AVCodecContext *avctx,
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
    H261Context *h= avctx->priv_data;
    MpegEncContext *s = &h->s;
    int ret;
    AVFrame *pict = data;

#ifdef DEBUG
    printf("*****frame %d size=%d\n", avctx->frame_number, buf_size);
    printf("bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
#endif
    s->flags= avctx->flags;
    s->flags2= avctx->flags2;

    /* no supplementary picture */
    if (buf_size == 0) {
        return 0;
    }

    if(s->flags&CODEC_FLAG_TRUNCATED){
        int next;

        next= h261_find_frame_end(&s->parse_context,avctx, buf, buf_size);

        if( ff_combine_frame(&s->parse_context, next, &buf, &buf_size) < 0 )
            return buf_size;
    }


retry:

    init_get_bits(&s->gb, buf, buf_size*8);

    if(!s->context_initialized){
        if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
            return -1;
    }

    //we need to set current_picture_ptr before reading the header, otherwise we cant store anyting im there
    if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
        int i= ff_find_unused_picture(s, 0);
        s->current_picture_ptr= &s->picture[i];
    }

    ret = h261_decode_picture_header(h);

    /* skip if the header was thrashed */
    if (ret < 0){
        av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
        return -1;
    }

    if (s->width != avctx->coded_width || s->height != avctx->coded_height){
        ParseContext pc= s->parse_context; //FIXME move these demuxng hack to avformat
        s->parse_context.buffer=0;
        MPV_common_end(s);
        s->parse_context= pc;
    }
    if (!s->context_initialized) {
        avcodec_set_dimensions(avctx, s->width, s->height);

        goto retry;
    }

    // for hurry_up==5
    s->current_picture.pict_type= s->pict_type;
    s->current_picture.key_frame= s->pict_type == I_TYPE;

    /* skip everything if we are in a hurry>=5 */
    if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);

    if(MPV_frame_start(s, avctx) < 0)
        return -1;

    ff_er_frame_start(s);

    /* decode each macroblock */
    s->mb_x=0;
    s->mb_y=0;

    while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
        if(ff_h261_resync(h)<0)
            break;
        h261_decode_gob(h);
    }
    MPV_frame_end(s);

assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
assert(s->current_picture.pict_type == s->pict_type);
    *pict= *(AVFrame*)&s->current_picture;
    ff_print_debug_info(s, pict);

    /* Return the Picture timestamp as the frame number */
    /* we substract 1 because it is added on utils.c    */
    avctx->frame_number = s->picture_number - 1;

    *data_size = sizeof(AVFrame);

    return get_consumed_bytes(s, buf_size);
}

static int h261_decode_end(AVCodecContext *avctx)
{
    H261Context *h= avctx->priv_data;
    MpegEncContext *s = &h->s;

    MPV_common_end(s);
    return 0;
}

AVCodec h261_encoder = {
    "h261",
    CODEC_TYPE_VIDEO,
    CODEC_ID_H261,
    sizeof(H261Context),
    MPV_encode_init,
    MPV_encode_picture,
    MPV_encode_end,
};

AVCodec h261_decoder = {
    "h261",
    CODEC_TYPE_VIDEO,
    CODEC_ID_H261,
    sizeof(H261Context),
    h261_decode_init,
    NULL,
    h261_decode_end,
    h261_decode_frame,
    CODEC_CAP_TRUNCATED,
};

AVCodecParser h261_parser = {
    { CODEC_ID_H261 },
    sizeof(ParseContext),
    NULL,
    h261_parse,
    ff_parse_close,
};