Always ensure you are downloading plugins from reputable sources like GitHub or the official app store. Avoid unverified third-party "decoder APKs" which may contain malware. Are you experiencing a specific error message

A for such a plugin means the plugin can be carried on a USB drive and used without formal installation—ideal for on-the-go use or locked-down workstations.

For a "portable" or manual installation when the in-app downloader fails, you can use these verified community resources: FFmpeg Plugin (GitHub):