c = get_byte(pb); len = (len << 7) | (c & 0x7f);
int c = get_byte(pb); len = (len << 7) | (c & 0x7f);
static int mp4_read_descr_len(ByteIOContext *pb){    int c, len, count;    len = 0;    count = 0;    for(;;) {        c = get_byte(pb);        len = (len << 7) | (c & 0x7f);        if ((c & 0x80) == 0)            break;        if (++count == 4)            break;    }    return len;}