I had an i5-7200u equipped laptop and I could do AV1 playback, not well but it didn’t do what you described.

Also is it maxing out memory or cpu? I would check btop during playback. Look at CPU usage, memory usage and temps while doing so and report here.

Edit: Something is definitely wrong with your machine, that is abnormal behavior. Maybe it’s overheating, maybe it’s trying to do some sort of gpu decode and has no idea what to do with it as it doesn’t support it. Can you check what encoder mpv is using? I would assume it would failback to CPU.

As others have said, you should probably replace your CPU fan ASAP.

A computer in usable condition does not shut down without user input.

The video playback should get choppy if the CPU is overloaded, the PC shouldn’t shut down from that. It sounds like your CPU may be overheating. I would suggest monitoring the CPU temperature while playing the video.

Modern CPUs (from like the last 20 years) will throttle down a lot before they actually shut down. Unless your cooling is completely inadequate or somehow broken, shutdowns because high load just dont happen. I suspect there is something fundamentally wrong with your hardware.

A problem with cooling could also go some way to explaining your performance problems – but it could also just be that your system just doesn’t have the computing power to do what you want it to. The computing demands from video decoding go up dramatically when you go beyond 1080p. If I recall correctly, the Intel Core CPUs with the “U” at the end were the low-energy models (for longer battery life); of course that comes with compromises on the performance side.

The CPU model suggests that this is a laptop, and a fairly old one at that. I would look for things like blocked air ducts or broken fans if I were you. It’s also possible that the thermal compound between your CPU and the CPU cooler has dried out and needs replacing (although laptops of that power class should be using thermal contact solutions that do not dry out), or that contact has lessened for other reasons. Again, if your computer seriously powers down because of load, it’s borderline broken and in need of maintenance.

As for your other question, no RAM cannot help with that. It can hurt if you have too little of it, but once you have enough, the best it can do is not be a bottleneck.

* Edit: Also, make sure you are not setting down the laptop on anything soft, like a blanket, when using it. It will sink in and have its air intakes blocked if you do that.

Aside from the other answers, no you can’t offload computations to memory. Memory stores data, it doesn’t compute.

The only way having more memory can possibly improve performance, is by having a cached copy of files so they don’t have to be fetched from disk, and applications potentially caching the results of heavy but reusable computations. (Unless you run out of memory and starts spilling over to disk, then more memory will make it fast again by avoiding swapping).

I mean I guess technically yes you could transcode into H264 into a tmpfs mount, and then play the H264, but you’re still not doing it faster and certainly not fast enough to watch in real time, you’re just decoding the AV1 well in advance before actually watching it.

For HEVC and AVC playback, your built-in GPU is used. Kaby lake doesn’t support AV1 hardware decoding so it’s hitting your CPU directly.

The shutdown could be a number of problems

1. Do you have high memory usage while playing AV1 videos?
2. Does the video start playing and then crash your system or is it an immediate crash?
3. Do you have swap space assigned and how much? Check with free -h
4. Are you having thermal issues? Do the fans kick in like crazy before shutdown or can you see very high temperatures with sensors?

no graphics card whatsoever

computer can play h.265 and equivalent without troubles, provided video file is no higher than 1080 p.

Computer can play av1 files no higher than 1080 p only if I shut every other application down. If for example I run a browser and an av1 file with either mpv or vlc, system shuts down.

Can I put all that memory to use and avoid overloading the cpu?

Most of the answers seem to focus on the main problem, but your question got me thinking.
Since you are not getting shutdowns with lower qualities, maybe you could use RAM to play those videos.
Set up tmpfs. Before you start all the other things, use ffmpeg to recode the video to something without any compression, maybe tell it to not work too fast (like work on one frame at a time), and put the thing on that tmpfs. Maybe then playing this new file would be less demanding. The key would be to not force it to provide 30fps of encoded video

Although… Are you sure all this RAM is fine? Maybe it shuts down on more demanding videos because with those the RAM usage raises to the faulty part?

As the other person said, something is wrong if your machine is shutting down instead of just giving choppy playback.

Do you do much heavy CPU with with that machine at all? It’s possible that AV1 decoding is the only thing you’re trying to do that pushes the CPU to that degree. 7th Gen Intel CPUs have hardware decoders for h.265, so the CPU is barely used to play these back, but lacking a decoder for AV1 means it has to be decoded in software, which hits the CPU hard.

It sounds like you are also possibly overheating. You don’t have hardware decoding for av1 on that computer so it’s all cpu work. But from my extensive use and testing with AV1 there is nothing about your hardware that should fail to play back 1080p 30fps av1 video.