The other alternative if the ffmpeg developers change the text on their "about" screen from "Security is a high priority and code review is always done with security in mind. Though due to the very large amounts of code touching untrusted data security issues are unavoidable and thus we provide as quick as possible updates to our last stable releases when new security issues are found." to something like "Security is a best-effort priority. Code review is always done with security in mind. Due to the very large amounts of code touching untrusted data security issues are unavoidable. We attempt to provide updates to our last stable releases when new security issues are found, but make no guarantees as to how long this may take. Priority will be given to reports including a proof-of-concept exploit and a patch that fixes the security bug."

Then point to the "PoC + Patch or GTFO" sign when reports come in. If you use a library with a "NO WARRANTY" license clause in an application where you're responsible for failures, it's on you to fix or mitigate the issues, not on the library authors.