Quick tip. It is possible to download media with small python script.
Goto https://my.telegram.org and generate api id and api hash
Install Telethon library with
pip3 install telethon
Run saveAllMedia.py (replace api_id, api_hash and username with your values).
If you need proxy install https://github.com/Anorov/PySocks
pip install PySocks
This code downloads all media from the dialog with username user/chat/channel in current directory.