nutdec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

    int64_t end, tmp;

    nut->last_syncpoint_pos= url_ftell(bc)-8;

    end= get_packetheader(nut, bc, 1, SYNCPOINT_STARTCODE);
    end += url_ftell(bc);

    tmp= get_v(bc);
    *back_ptr= nut->last_syncpoint_pos - 16*get_v(bc);
    if(*back_ptr < 0)
        return -1;

    ff_nut_reset_ts(nut, nut->time_base[tmp % nut->time_base_count], tmp);

    if(skip_reserved(bc, end) || get_checksum(bc)){
        av_log(s, AV_LOG_ERROR, "sync point checksum mismatch\n");
        return -1;
    }

    *ts= tmp / s->nb_streams * av_q2d(nut->time_base[tmp % s->nb_streams])*AV_TIME_BASE;
    ff_nut_add_sp(nut, nut->last_syncpoint_pos, *back_ptr, *ts);

    return 0;
}

static int find_and_decode_index(NUTContext *nut){
    AVFormatContext *s= nut->avf;
    ByteIOContext *bc = &s->pb;
    uint64_t tmp, end;
    int i, j, syncpoint_count;
    int64_t filesize= url_fsize(bc);
    int64_t *syncpoints;
    int8_t *has_keyframe;

    url_fseek(bc, filesize-12, SEEK_SET);
    url_fseek(bc, filesize-get_be64(bc), SEEK_SET);
    if(get_be64(bc) != INDEX_STARTCODE){
        av_log(s, AV_LOG_ERROR, "no index at the end\n");
        return -1;
    }

    end= get_packetheader(nut, bc, 1, INDEX_STARTCODE);
    end += url_ftell(bc);

    get_v(bc); //max_pts
    GET_V(syncpoint_count, tmp < INT_MAX/8 && tmp > 0)
    syncpoints= av_malloc(sizeof(int64_t)*syncpoint_count);
    has_keyframe= av_malloc(sizeof(int8_t)*(syncpoint_count+1));
    for(i=0; i<syncpoint_count; i++){
        GET_V(syncpoints[i], tmp>0)
        if(i)
            syncpoints[i] += syncpoints[i-1];
    }

    for(i=0; i<s->nb_streams; i++){
        int64_t last_pts= -1;
        for(j=0; j<syncpoint_count;){
            uint64_t x= get_v(bc);
            int type= x&1;
            int n= j;
            x>>=1;
            if(type){
                int flag= x&1;
                x>>=1;
                if(n+x >= syncpoint_count + 1){
                    av_log(s, AV_LOG_ERROR, "index overflow A\n");
                    return -1;
                }
                while(x--)
                    has_keyframe[n++]= flag;
                has_keyframe[n++]= !flag;
            }else{
                while(x != 1){
                    if(n>=syncpoint_count + 1){
                        av_log(s, AV_LOG_ERROR, "index overflow B\n");
                        return -1;
                    }
                    has_keyframe[n++]= x&1;
                    x>>=1;
                }
            }
            if(has_keyframe[0]){
                av_log(s, AV_LOG_ERROR, "keyframe before first syncpoint in index\n");
                return -1;
            }
            assert(n<=syncpoint_count+1);
            for(; j<n; j++){
                if(has_keyframe[j]){
                    uint64_t B, A= get_v(bc);
                    if(!A){
                        A= get_v(bc);
                        B= get_v(bc);
                        //eor_pts[j][i] = last_pts + A + B
                    }else
                        B= 0;
                    av_add_index_entry(
                        s->streams[i],
                        16*syncpoints[j-1],
                        last_pts + A,
                        0,
                        0,
                        AVINDEX_KEYFRAME);
                    last_pts += A + B;
                }
            }
        }
    }

    if(skip_reserved(bc, end) || get_checksum(bc)){
        av_log(s, AV_LOG_ERROR, "index checksum mismatch\n");
        return -1;
    }
    return 0;
}

static int nut_read_header(AVFormatContext *s, AVFormatParameters *ap)
{
    NUTContext *nut = s->priv_data;
    ByteIOContext *bc = &s->pb;
    int64_t pos;
    int inited_stream_count;

    nut->avf= s;

    /* main header */
    pos=0;
    do{
        pos= find_startcode(bc, MAIN_STARTCODE, pos)+1;
        if (pos<0+1){
            av_log(s, AV_LOG_ERROR, "No main startcode found.\n");
            return -1;
        }
    }while(decode_main_header(nut) < 0);

    /* stream headers */
    pos=0;
    for(inited_stream_count=0; inited_stream_count < s->nb_streams;){
        pos= find_startcode(bc, STREAM_STARTCODE, pos)+1;
        if (pos<0+1){
            av_log(s, AV_LOG_ERROR, "Not all stream headers found.\n");
            return -1;
        }
        if(decode_stream_header(nut) >= 0)
            inited_stream_count++;
    }

    /* info headers */
    pos=0;
    for(;;){
        uint64_t startcode= find_any_startcode(bc, pos);
        pos= url_ftell(bc);

        if(startcode==0){
            av_log(s, AV_LOG_ERROR, "EOF before video frames\n");
            return -1;
        }else if(startcode == SYNCPOINT_STARTCODE){
            nut->next_startcode= startcode;
            break;
        }else if(startcode != INFO_STARTCODE){
            continue;
        }

        decode_info_header(nut);
    }

    s->data_offset= pos-8;

    if(!url_is_streamed(bc)){
        int64_t orig_pos= url_ftell(bc);
        find_and_decode_index(nut);
        url_fseek(bc, orig_pos, SEEK_SET);
    }
    assert(nut->next_startcode == SYNCPOINT_STARTCODE);

    return 0;
}

static int decode_frame_header(NUTContext *nut, int64_t *pts, int *stream_id, int frame_code){
    AVFormatContext *s= nut->avf;
    ByteIOContext *bc = &s->pb;
    StreamContext *stc;
    int size, flags, size_mul, pts_delta, i, reserved_count;
    uint64_t tmp;

    if(url_ftell(bc) > nut->last_syncpoint_pos + nut->max_distance){
        av_log(s, AV_LOG_ERROR, "Last frame must have been damaged %"PRId64" > %"PRId64" + %d\n", url_ftell(bc), nut->last_syncpoint_pos, nut->max_distance);
        return -1;
    }

    flags          = nut->frame_code[frame_code].flags;
    size_mul       = nut->frame_code[frame_code].size_mul;
    size           = nut->frame_code[frame_code].size_lsb;
    *stream_id     = nut->frame_code[frame_code].stream_id;
    pts_delta      = nut->frame_code[frame_code].pts_delta;
    reserved_count = nut->frame_code[frame_code].reserved_count;

    if(flags & FLAG_INVALID)
        return -1;
    if(flags & FLAG_CODED)
        flags ^= get_v(bc);
    if(flags & FLAG_STREAM_ID){
        GET_V(*stream_id, tmp < s->nb_streams)
    }
    stc= &nut->stream[*stream_id];
    if(flags&FLAG_CODED_PTS){
        int coded_pts= get_v(bc);
//FIXME check last_pts validity?
        if(coded_pts < (1<<stc->msb_pts_shift)){
            *pts=ff_lsb2full(stc, coded_pts);
        }else
            *pts=coded_pts - (1<<stc->msb_pts_shift);
    }else
        *pts= stc->last_pts + pts_delta;
    if(flags&FLAG_SIZE_MSB){
        size += size_mul*get_v(bc);
    }
    if(flags&FLAG_RESERVED)
        reserved_count= get_v(bc);
    for(i=0; i<reserved_count; i++)
        get_v(bc);
    if(flags&FLAG_CHECKSUM){
        get_be32(bc); //FIXME check this
    }else if(size > 2*nut->max_distance || FFABS(stc->last_pts - *pts) > stc->max_pts_distance){
        av_log(s, AV_LOG_ERROR, "frame size > 2max_distance and no checksum\n");
        return -1;
    }

    stc->last_pts= *pts;
    stc->last_flags= flags;

    return size;
}

static int decode_frame(NUTContext *nut, AVPacket *pkt, int frame_code){
    AVFormatContext *s= nut->avf;
    ByteIOContext *bc = &s->pb;
    int size, stream_id, discard;
    int64_t pts, last_IP_pts;
    StreamContext *stc;

    size= decode_frame_header(nut, &pts, &stream_id, frame_code);
    if(size < 0)
        return -1;

    stc= &nut->stream[stream_id];

    if (stc->last_flags & FLAG_KEY)
        stc->skip_until_key_frame=0;

    discard= s->streams[ stream_id ]->discard;
    last_IP_pts= s->streams[ stream_id ]->last_IP_pts;
    if(  (discard >= AVDISCARD_NONKEY && !(stc->last_flags & FLAG_KEY))
       ||(discard >= AVDISCARD_BIDIR && last_IP_pts != AV_NOPTS_VALUE && last_IP_pts > pts)
       || discard >= AVDISCARD_ALL
       || stc->skip_until_key_frame){
        url_fskip(bc, size);
        return 1;
    }

    av_get_packet(bc, pkt, size);
    pkt->stream_index = stream_id;
    if (stc->last_flags & FLAG_KEY)
        pkt->flags |= PKT_FLAG_KEY;
    pkt->pts = pts;

    return 0;
}

static int nut_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    NUTContext *nut = s->priv_data;
    ByteIOContext *bc = &s->pb;
    int i, frame_code=0, ret, skip;
    int64_t ts, back_ptr;

    for(;;){
        int64_t pos= url_ftell(bc);
        uint64_t tmp= nut->next_startcode;
        nut->next_startcode=0;

        if(tmp){
            pos-=8;
        }else{
            frame_code = get_byte(bc);
            if(url_feof(bc))
                return -1;
            if(frame_code == 'N'){
                tmp= frame_code;
                for(i=1; i<8; i++)
                    tmp = (tmp<<8) + get_byte(bc);
            }
        }
        switch(tmp){
        case MAIN_STARTCODE:
        case STREAM_STARTCODE:
        case INDEX_STARTCODE:
            skip= get_packetheader(nut, bc, 0, tmp);
            url_fseek(bc, skip, SEEK_CUR);
            break;
        case INFO_STARTCODE:
            if(decode_info_header(nut)<0)
                goto resync;
            break;
        case SYNCPOINT_STARTCODE:
            if(decode_syncpoint(nut, &ts, &back_ptr)<0)
                goto resync;
            frame_code = get_byte(bc);
        case 0:
            ret= decode_frame(nut, pkt, frame_code);
            if(ret==0)
                return 0;
            else if(ret==1) //ok but discard packet
                break;
        default:
resync:
av_log(s, AV_LOG_DEBUG, "syncing from %"PRId64"\n", pos);
            tmp= find_any_startcode(bc, nut->last_syncpoint_pos+1);
            if(tmp==0)
                return -1;
av_log(s, AV_LOG_DEBUG, "sync\n");
            nut->next_startcode= tmp;
        }
    }
}

static int64_t nut_read_timestamp(AVFormatContext *s, int stream_index, int64_t *pos_arg, int64_t pos_limit){
    NUTContext *nut = s->priv_data;
    ByteIOContext *bc = &s->pb;
    int64_t pos, pts, back_ptr;
av_log(s, AV_LOG_DEBUG, "read_timestamp(X,%d,%"PRId64",%"PRId64")\n", stream_index, *pos_arg, pos_limit);

    pos= *pos_arg;
    do{
        pos= find_startcode(bc, SYNCPOINT_STARTCODE, pos)+1;
        if(pos < 1){
            assert(nut->next_startcode == 0);
            av_log(s, AV_LOG_ERROR, "read_timestamp failed.\n");
            return AV_NOPTS_VALUE;
        }
    }while(decode_syncpoint(nut, &pts, &back_ptr) < 0);
    *pos_arg = pos-1;
    assert(nut->last_syncpoint_pos == *pos_arg);

    av_log(s, AV_LOG_DEBUG, "return %"PRId64" %"PRId64"\n", pts,back_ptr );
    if     (stream_index == -1) return pts;
    else if(stream_index == -2) return back_ptr;

assert(0);
}

static int read_seek(AVFormatContext *s, int stream_index, int64_t pts, int flags){
    NUTContext *nut = s->priv_data;
    AVStream *st= s->streams[stream_index];
    syncpoint_t dummy={.ts= pts*av_q2d(st->time_base)*AV_TIME_BASE};
    syncpoint_t nopts_sp= {.ts= AV_NOPTS_VALUE, .back_ptr= AV_NOPTS_VALUE};
    syncpoint_t *sp, *next_node[2]= {&nopts_sp, &nopts_sp};
    int64_t pos, pos2, ts;
    int i;

    if(st->index_entries){
        int index= av_index_search_timestamp(st, pts, flags);
        if(index<0)
            return -1;

        pos2= st->index_entries[index].pos;
        ts  = st->index_entries[index].timestamp;
    }else{
        av_tree_find(nut->syncpoints, &dummy, ff_nut_sp_pts_cmp, next_node);
        av_log(s, AV_LOG_DEBUG, "%"PRIu64"-%"PRIu64" %"PRId64"-%"PRId64"\n", next_node[0]->pos, next_node[1]->pos,
                                                    next_node[0]->ts , next_node[1]->ts);
        pos= av_gen_search(s, -1, dummy.ts, next_node[0]->pos, next_node[1]->pos, next_node[1]->pos,
                                            next_node[0]->ts , next_node[1]->ts, AVSEEK_FLAG_BACKWARD, &ts, nut_read_timestamp);

        if(!(flags & AVSEEK_FLAG_BACKWARD)){
            dummy.pos= pos+16;
            next_node[1]= &nopts_sp;
            av_tree_find(nut->syncpoints, &dummy, ff_nut_sp_pos_cmp, next_node);
            pos2= av_gen_search(s, -2, dummy.pos, next_node[0]->pos     , next_node[1]->pos, next_node[1]->pos,
                                                next_node[0]->back_ptr, next_node[1]->back_ptr, flags, &ts, nut_read_timestamp);
            if(pos2>=0)
                pos= pos2;
            //FIXME dir but i think it does not matter
        }
        dummy.pos= pos;
        sp= av_tree_find(nut->syncpoints, &dummy, ff_nut_sp_pos_cmp, NULL);

        assert(sp);
        pos2= sp->back_ptr  - 15;
    }
    av_log(NULL, AV_LOG_DEBUG, "SEEKTO: %"PRId64"\n", pos2);
    pos= find_startcode(&s->pb, SYNCPOINT_STARTCODE, pos2);
    url_fseek(&s->pb, pos, SEEK_SET);
    av_log(NULL, AV_LOG_DEBUG, "SP: %"PRId64"\n", pos);
    if(pos2 > pos || pos2 + 15 < pos){
        av_log(NULL, AV_LOG_ERROR, "no syncpoint at backptr pos\n");
    }
    for(i=0; i<s->nb_streams; i++)
        nut->stream[i].skip_until_key_frame=1;

    return 0;
}

static int nut_read_close(AVFormatContext *s)
{
    NUTContext *nut = s->priv_data;

    av_freep(&nut->time_base);
    av_freep(&nut->stream);

    return 0;
}

#ifdef CONFIG_NUT_DEMUXER
AVInputFormat nut_demuxer = {
    "nut",
    "nut format",
    sizeof(NUTContext),
    nut_probe,
    nut_read_header,
    nut_read_packet,
    nut_read_close,
    read_seek,
    .extensions = "nut",
};
#endif