(1) Remember AE can only use 4 GB of RAM to build RAM previews, due to the limitations of 32bit applications. The soon-to-be-launched AE CS5 will be able to directly address much more RAM. Try purging your RAM occasionally from the Edit menu. You may need to turn off multi-processing during the design stage, or checking you haven't allocated too much RAM to other applications. Try to limit the other applications running at the same time as AE.
(2) You need to change spatial interpolation to Linear. Select the problem keyframes and choose Animation/Keyframe Interpolation, then set Spatial Interpolation to Linear.
In AE Preferences you can set the default spatial interpolation to always be linear, if this is a continuing issue for you.
Hello Thanks for your helpful reply
1) When I purged my RAM my preview lenth (2 seconds) stayed the same. When I turned off multi-processing my preview lenth doubled (4 seconds). I have it set to 7.5 GB for AE and .5 for other applications.. Also I only have firefox running at the same time, and even without firefox my preview lenth stays the same. Yesterday and other days I was able to preview any video succesffly.. not just 3 seconds of it so I dont know why I can only preview 4? Any more suggestions? This preview thing is keeping me from working on a project because since it is a typography the letters have to match the audio so I have preview the video frequently so make sure everything is right.
2) I changed the spatial interpolation to linear and this solved my problem. Thank you very much
Any other suggestions for my first problem.. It started yesterday and before that everything worked fine..
You can also lower the RAM preview resolution to Quarter or even lower if you're working at very high resolution.
Hope that helps,