Is it possible to have a single input or output with multiple addresses

Question

I've seen in more than one Blockchain API provider's specs where the transaction inputs and outputs are in the following format:

addresses: ARRAY
The address (or addresses in the case of multi-sig) to which the value was transferred.

I'm confused about the array. When I try these APIs with a transaction where one of the outputs is to a multi sig address, I still see a single multi-sig address in the output.

In which cases would I see multiple addresses in a single output or input?

This the same in these api providers:

https://chain.com/docs#object-bitcoin-transaction

http://dev.blockcypher.com/#transactions

https://toshi.io/docs/#get-transaction

Answer 1

The answer here is escrow outputs.

When one of the outputs is sent to escrow, the related addresses are listed in those arrays.

Here is an example: https://insight.bitpay.com/api/tx/09dd94f2c85262173da87a745a459007bb1eed6eeb6bfa238a0cd91a16cf7790

A single output will be displayed to have multiple addresses.

Blockcypher's API will show an address starting with 4 instead of multiple adresses. And output script type = pay-to-multi-pubkey-hash

{
      "value": 10860,
      "script": "5121032487c2a32f7c8d57d2a93906a6457afd00697925b0e6e145d89af6d3bca330162102308673d16987eaa010e540901cc6fe3695e758c19f46ce604e174dac315e685a52ae",
      "addresses": [
        "4bkHBecr4EQvVUa8Lsa2kH6rGtvsC9AZ5Y"
      ],
      "script_type": "pay-to-multi-pubkey-hash"
    },

Answer 2

Each transaction can be made of many different inputs and many different outputs. Each output must reference 1 output address and each input must reference 1 input transaction. So the inputs and outputs can only reference a single address each but the transaction itself can reference many.

As far as multi sig goes that merely referees to the amount of private keys used to sign the transaction which is independent of the addresses.