I have about 100x as much sympathy for an open source project getting time to fix a security bug than I do a multibillion dollar company with nearly infinite resources essentially blackmailing a small team of developers like this. They could -easily- pay a dev to fix the bug and send the fix to ffmpeg.
Since when are bug reports blackmail? If some retro game enthusiast discovered this bug and made a blog post about it that went to the front page of HN, is that blackmail? If someone running a fuzzer found this bug and dumped a public bug report into github is that blackmail? What if google made this report privately, but didn't say anything about when they would make it public and then just went public at some arbitrary time in the future? How is "heads up, here's a bug we found, here's the reproduction steps for it, we'll file a public bug report on it soon" blackmail?