File ids are personal and bound to a specific user/bot -- and an attempt in using a foreign file id will result in

errors such as ``[400 MEDIA_EMPTY]``.

Definitely! All file ids you might have taken from the Bot API are 100% compatible and re-usable in Pyrogram.

**However...**

Telegram is slowly changing some server's internals and it's doing it in such a way that file ids are going to break

inevitably. Not only this, but it seems that the new, hypothetical, file ids could also possibly expire at anytime, thus

losing the *persistence* feature (see `What is a file_ref and why do I need it?`_).

This change will most likely affect the official :doc:`Bot API <topics/mtproto-vs-botapi>` too (unless Telegram

implements some workarounds server-side to keep backwards compatibility, which Pyrogram could in turn make use of) and

we can expect a proper notice from Telegram.

- The chat id refers to a user your current session haven't met yet.

for usernames, meeting them in a common group, have their phone contacts saved or getting a message mentioning them,

either a forward or a mention in the message text.

What is a file_ref and why do I need it?

.. note::

This FAQ is currently applicable to user accounts only. Bot accounts are still doing fine without a file_ref

(even though this can change anytime since it's a Telegram's internal server behaviour).

Similarly to what happens with users and chats which need to first be encountered in order to interact with them, media

messages also need to be "seen" recently before downloading or re-sending without uploading as new file.

**What is it meant by "they need to be seen recently"?**

That means you have to fetch the original media messages prior any action in order to get a valid and up to date value

called file reference (file_ref) which, in pair with a file_id, enables you to interact with the media. This file_ref

value won't last forever (usually 24h, but could expire anytime) and in case of errors you have to get a refreshed

file_ref by re-fetching the original message (fetching forwarded media messages does also work).

**Ok, but what is a file_ref actually needed for?**

Nobody knows for sure, but is likely because that's the correct approach for handling tons of files uploaded by users in

Telegram's cloud. Which means, as soon as the media message still exists, a valid file_ref can be obtained, otherwise,

in case there's no more messages referencing a specific media, Telegram is able to free disk space by deleting old

files.