PeerStreamer

/*

 * H261 decoder

 * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>

 * Copyright (c) 2004 Maarten Daniels

 *

 * This file is part of Libav.

 *

 * Libav 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 2.1 of the License, or (at your option) any later version.

 *

 * Libav 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 Libav; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * H.261 decoder.

 */

#include "dsputil.h"

#include "avcodec.h"

#include "mpegvideo.h"

#include "h263.h"

#include "h261.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

extern uint8_t ff_h261_rl_table_store[2][2*MAX_RUN + MAX_LEVEL + 3];

static VLC h261_mba_vlc;

static VLC h261_mtype_vlc;

static VLC h261_mv_vlc;

static VLC h261_cbp_vlc;

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

static av_cold void h261_decode_init_vlc(H261Context *h){

    static int done = 0;

    if(!done){

        done = 1;

        INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,

                 h261_mba_bits, 1, 1,

                 h261_mba_code, 1, 1, 662);

        INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,

                 h261_mtype_bits, 1, 1,

                 h261_mtype_code, 1, 1, 80);

        INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,

                 &h261_mv_tab[0][1], 2, 1,

                 &h261_mv_tab[0][0], 2, 1, 144);

        INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,

                 &h261_cbp_tab[0][1], 2, 1,

                 &h261_cbp_tab[0][0], 2, 1, 512);

        init_rl(&h261_rl_tcoeff, ff_h261_rl_table_store);

        INIT_VLC_RL(h261_rl_tcoeff, 552);

    }

}

static av_cold 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 occurred

 */

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) {

        av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");

        if (s->avctx->error_recognition >= FF_ER_COMPLIANT)

            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, it is not where it is supposed to be ...

        s->gb= s->last_resync_gb;

        align_get_bits(&s->gb);

        left= get_bits_left(&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);

        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_skipped = 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);

    // 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)){

        s->dsp.clear_blocks(s->block[0]);

        for (i = 0; i < 6; i++) {

            if (h261_decode_block(h, s->block[i], i, cbp&32) < 0){

                return SLICE_ERROR;

            }

            cbp+=cbp;

        }

    }else{

        for (i = 0; i < 6; i++)

            s->block_last_index[i]= -1;

    }

    MPV_decode_mb(s, s->block);

    return SLICE_OK;

}

/**

 * decodes a macroblock

 * @return <0 if an error occurred

 */

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 = get_sbits(&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

 */

static int h261_decode_picture_header(H261Context *h){

    MpegEncContext * const s = &h->s;

    int format, i;

    uint32_t startcode= 0;

    for(i= get_bits_left(&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 */

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

    if(i < (s->picture_number&31))

        i += 32;

    s->picture_number = (s->picture_number&~31) + i;

    s->avctx->time_base= (AVRational){1001, 30000};

    s->current_picture.pts= s->picture_number;

    /* 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 FF_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 = FF_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;

}

/**

 * returns the number of bytes consumed for building the current frame

 */

static int get_consumed_bytes(MpegEncContext *s, int buf_size){

    int pos= get_bits_count(&s->gb)>>3;

    if(pos==0) pos=1; //avoid infinite loops (i doubt that is 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,

                             AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    H261Context *h= avctx->priv_data;

    MpegEncContext *s = &h->s;

    int ret;

    AVFrame *pict = data;

    av_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);

    av_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);

    s->flags= avctx->flags;

    s->flags2= avctx->flags2;

    h->gob_start_code_skipped=0;

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 cannot 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 this demuxing hack to libavformat

        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 skipping the frame

    s->current_picture.pict_type= s->pict_type;

    s->current_picture.key_frame= s->pict_type == FF_I_TYPE;

#if FF_API_HURRY_UP

    /* skip everything if we are in a hurry>=5 */

    if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);

#endif

    if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==FF_B_TYPE)

       ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=FF_I_TYPE)

       || avctx->skip_frame >= AVDISCARD_ALL)

        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_ptr;

    ff_print_debug_info(s, pict);

    *data_size = sizeof(AVFrame);

    return get_consumed_bytes(s, buf_size);

}

static av_cold int h261_decode_end(AVCodecContext *avctx)

{

    H261Context *h= avctx->priv_data;

    MpegEncContext *s = &h->s;

    MPV_common_end(s);

    return 0;

}

AVCodec ff_h261_decoder = {

    "h261",

    AVMEDIA_TYPE_VIDEO,

    CODEC_ID_H261,

    sizeof(H261Context),

    h261_decode_init,

    NULL,

    h261_decode_end,

    h261_decode_frame,

    CODEC_CAP_DR1,

    .max_lowres = 3,

    .long_name = NULL_IF_CONFIG_SMALL("H.261"),

};