s->size= buffer_size;
void init_get_bits(GetBitContext *s,                    UINT8 *buffer, int buffer_size){#ifdef ALT_BITSTREAM_READER    s->index=0;    s->buffer= buffer;#else    s->buf = buffer;    s->buf_ptr = buffer;    s->buf_end = buffer + buffer_size;    s->bit_cnt = 0;    s->bit_buf = 0;    while (s->buf_ptr < s->buf_end &&            s->bit_cnt < 32) {        s->bit_buf |= (*s->buf_ptr++ << (24 - s->bit_cnt));        s->bit_cnt += 8;    }#endif}