h261dec.c

mediastreamer2是开源的网络传输媒体流的库

/*
 * H261 decoder
 * Copyright (c) 2002-2004 Michael Niedermayer <[e-mail]>
 * Copyright (c) 2004 Maarten Daniels
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file h261dec.c
 * H.261 decoder.
 */

#include "dsputil.h"
#include "avcodec.h"
#include "mpegvideo.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 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, 1);
        init_vlc(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
                 h261_mtype_bits, 1, 1,
                 h261_mtype_code, 1, 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, 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, 1);
        init_rl(&h261_rl_tcoeff, ff_h261_rl_table_store);
        init_vlc_rl(&h261_rl_tcoeff, 1);
    }
}

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, it is not where it is 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);

        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