Per Todd Kopriva, posting in another thread [link]: What happens if you mute audio in the Preview panel? (This question is getting at a possible problem in how audio is cached first before the video RAM preview begins.)
Failing that, a quick note on how Ae’s multiprocessing works: it saves a copy of your project, then multiple instances of the Ae renderer open that project, each within its own RAM space, and thus render multiple frames simultaneously.
As you note, there is a lot of time overhead for starting up multiprocessing: saving the project, launching the background renderers, and then each instance opening the project — all before a single frame is rendered.
For short renders, this overhead is not always worth it; it may be faster just to render a single frame at a time because this incurs no overhead. This is why there’s a preference to disable MP for RAM previews.
For longer renders, though, the ability to render multiple frames at the same time usually eventually pays back the overhead of starting the multiprocessing render in the first place. This is why there’s a preference to leave MP on for render when it’s disabled for RAM previews.
In other words, a 25 second render will probably not benefit from multiprocessing (especially if your apps and projects are not stored on SSD drives), but a 5 minute render will.
I think it’s bad practice to leave 0 CPUs for other applications. This leads to overscheduled processors [link]. 2GB is also probably the minimum reasonable allocation for each process, and you might see better results with a higher minimum allocation — but make sure you are also reserving enough RAM (I usually start at 25%) for other applications.
I think you will generally see better results reserving 8GB (or more) for other applications, reserving 6 CPUs (or more) for other applications, and allocating 4 GB (or more) for each background process, even though this will reduce the number of render threads.
I know that seems paradoxical — but fewer render threads with sufficient resources trump more render threads with insufficient resources, with faster total render times.
Personally, I usually leave MP for RAM preview off because I cannot tolerate that lengthy startup time for just a few frames. You might consider using the cache work area in background feature to speed up single-process RAM previews where possible.
Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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