A solution definitely ought to be found. Google putting up a few millionths of a percent of their revenue or so towards fixing the bugs they find in ffmpeg would be the ideal solution here, certainly. Yet it seems unlikely to actually occur.
I think the far more likely result of all the complaints is that Google simply completely disengages from ffmpeg and stops doing any security work on it. I think that would be quite bad for the security of the project - if Google can trivially find bugs at a high speed such that it overwhelms the ffmpeg developers, I would imagine bad actors can also search for them and find those same vulnerabilities Google is constantly finding, and if they know that those vulnerabilities very much exist, but that Google has simply stopped searching for them upon demand of the ffmpeg project, this would likely give them extremely high motivation to go looking in a place they can be almost certain they'll find unreported/unknown vulnerabilities in. The result would likely be a lot more 0-day attacks involving ffmpeg, which I do not think anyone regards as a good outcome (I would consider "Google publishes a bunch of vulnerabilities ffmpeg hasn't fixed so that everyone knows about them" to be a much preferable outcome, personally)
Now, you might consider that possibility fine - after all, the ffmpeg developers have no obligation to work on the project, and thus to e.g. fix any vulnerabilities in it. But if that's fine, then simply ignoring the reports Google currently makes is presumably also fine, no ?