In terminal.app, install ffmpeg through homebrew
brew install ffmpeg
Validate the installation:
Gitlab won't allow reuse of a public ssh key for multiple accounts. To get around this you need to create a second ssh key for the second account.
Create or modify your ~/.ssh/config
file:
# normal
Host gitlab.com-work_username
HostName gitlab.com
PreferredAuthentications publickey
IdentityFile ~/.ssh/id_rsa