void ff_update_duplicate_context(MpegEncContext *dst, MpegEncContext *src){
    MpegEncContext bak;
    int i;
    //FIXME copy only needed parts
//START_TIMER
    backup_duplicate_context(&bak, dst);
    memcpy(dst, src, sizeof(MpegEncContext));
    backup_duplicate_context(dst, &bak);
    for(i=0;i<12;i++){
        dst->pblocks[i] = &dst->block[i];
    }
//STOP_TIMER("update_duplicate_context") //about 10k cycles / 0.01 sec for 1000frames on 1ghz with 2 threads
}