I am having similar issues, but mine seems to not catch up. It may be waiting on memory......how much do you have? Cmax

Quote: All of a sudden some of my video clips on the timeline are freezing on playback, then speeding up to catch up with the audio. Sometimes the scrubber, which is supposed to move with the video, skips ahead to the last clip while the video and audio are still playing the clip I am working on. What is going on here?

Very often related to 1) Video Card and driver and 2) Shadow files. You didn;t give us any information on what you have so it is difficult to make a good assessment. The first thing I'd try is to turn off the shadow files in preferences. .
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Peter and Cmax,
your problems with poor timeline playback may be two different issues, so keep that in mind.
The scrubber and playback may also have poor performance if you use FX, or implement fixes for color, etc, that causes your computer to struggle.
In playback, you have to understand that your machine is attempting create your video, and any alterations, on-the-fly, and some just cannot keep up.
To add to the list, playback can be affected by:
File type and bitrate of your video.
Smartsound (stops my i7 in it's tracks, totally unusable).
Too many FX. Lower your preview quality to ease strain on your machine. Click the box icon under the preview window, between the camera and speaker icons.
The location of your media. Files should be on a fast internal drive.
Computer maintenance and ample free space on your C drive.
Other programs running in the background.
There are very few things that reveal the weakness of a machine like video editing, it's quite demanding.

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Nvidia GTX 960(4GB)/16GB DDR3/
Canon Vixia HV30/HF-M40/HF-M41/HF-G20/Olympus E-PL5.
Tape capture using 6 VCR, TBC-1000, Elite BVP4+, Sony D8 camcorder with TBC.
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Thanks for all these ideas. I tried removing the shadow files and then kept the task manager on as I previewed my video, and the CPU usage kept going up to 90-98%, so it looks like I just dont have enough RAM (I currently have only 3GB and have ordered a 12GB machine.) When it comes in, I'll try again.

This is a great forum. Thanks for all all your timely input on my problems!

thanks for the info...So the playback is affected but what about the video? If I continue and produce it, will it be modified and play with the changes with no problems?
And how do I lower the play back quality?

thanks Again Cmax