A question that is heard an awful lot is this: What is the functional difference between a RAM preview and a standard (or Spacebar) preview. Here’s a quick breakdown of the differences between the two:
*Plays in realtime. What you see is what you will get, in terms of timing
*You do not see placeholders for lights, cameras, or otherwise invisible objects in your scene. This is helpful if you want to get a sense of what your final render will be.
*Stored in RAM, stops rendering preview frames when RAM storage has reached its limit.
Standard (Spacebar) Preview:
*Does not play in realtime
*You see placeholders for lights, cameras, or otherwise invisible objects in the scene. This is helpful if you want to see how those objects are moving around in the scene.
*Initially frames are stored in RAM as the preview renders out, but are stored on scratch disk as additional frames are rendered when RAM has filled.
Both RAM and Standard Previews are similar in the following regards:
*Both obey the Preview settings in the Preview Panel
*Both are limited to the Work Area defined in the Timeline panel
I hope that this breakdown enables you to make more informed choices as you select which preview is best in a given situation!