AE is a 32bit application, and on a 32bit OS (and even on a G4bit OS) it can only access to a theorical maximum of 4gb of ram per process.
If you are using Mac OS, AE wil see something around 3,5gb of ram (the 0,5 are used by macOS), on windows 32bit AE will see 2gb (up to 3gb if you use a specific switch. Win is limiting app to 2gb of ram), and on windows 64bit (and mac 64bit) AE will be around 3,8-4gb or Ram.
Now, you have to understand how the AE render engine works so you can avoid the buffer problems. In order to render a frame, AE needs to load it uncompressed inside your RAM. What does it mean ? It means that if your image can't fit uncompressed in your ram, you'll get that error message.
Here is how to calculate to see if your image will fit.
Each pixel of your image have 4 channels, R,G,B & Alpha. Each channel use 8 to 32bits depending on your project bit depth.
A full HD image for exemple will fill 1920x1080x4x8 bits in ram in 8 bit mode, a 4 times more in 32bit mode. And it must fit in one continuous chunk of Ram. Add to that any memory intensive effects (keylight for exemple), and the fact that AE caches some info in ram too to speed up the render and you'll see that you'll soon be limited in the max size of your asset.
> In the RAM menu where you can allocate RAM, it says that I only have 3gb installed, however, my computer is a Quad core, 8GB RAM machine (which is why I'm incredulous that it's behaving so badly). Does AE usually not use the whole RAM available, or is this a case whereby it's somehow not noticing my full RAM potential?
Here's an FAQ entry that gives some more information, in addition to the very good answer from Sebastien:
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Oups posted before finishing.
Anyway, the thing that most matters is the size of your sources. You can also try to use the secret menu to deactivate the caching during the render.
For that hold the shift key and then go to edit > preferences > general.
Once the dialog open, release Shift and a secret element has been added in the pref lists. To use in last ressort.
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it says that I only have 3gb installed, however, my computer is a Quad core, 8GB RAM
As the others said AE is still a 32bit app. It can only use "more" RAM by ways of using multiprocessing, ideally on 64bit operating systems. For that, 8 GB may not even be enouzgh, depending on how many cores you use. Anyway, getting crashes with "simple" projects is always suspicious and points to more systemic issues. So please provide some more detailed info about your operating system, graphics card, waht footages you use, what prefs in AE, what render settings. The whole thing might be a combination of all the differnt things, not just a single cause.
Thanks for your responses. In terms of the crashing and image buffering, I managed to fix it. For some reason it was just a dodgy image file that was actually quite small, but AE seemed confused when claiming it was about 5000px x 5000px. I just deleted it and it's all good.
Thanks for your explanations regarding the RAM, taught me alot I didn't know. I looked into the multiprocessing menu, and I've turned it on. However, it only allows me to use 1 core, and no more than that. Further still, when I turn it on, it says in the RAM preview window 'Insufficient RAM.Multiprocessing turned off' - It's not an error, it just likes to make me aware. Should I theoretically have the option to use more cores?
Is it possible that you're on Windows XP 32 bit? In that OS, the total available RAM for all applications (ie, not per application/process) is 2.7 GB. That makes multiprocessing nearly pointless. In Vista 32 this limitation doesn't exist, although moving to Vista 64 is better.
Yeah, I concur with teh previous. If you are running on 32bit Windows, you will not be able to use MP because the routines, no matter how smart they are otehrwise, have no way of establishing a separate isolated memory area to hold the otehr instances of AE that would do the background rendering. Only on a 64bit OS do you get this to work in most cases, unfortunately.