[Peter Herman]

Thanks for the info Norman – it is a bit clearer now.

However it appears the problem is a bit more fundamental than the video size.

Today I experimented with a lower quality video from a different source. It’s spec is –
Maximum bit rate : 25.0 Mbps
Width : 1 280 pixels
Height : 528 pixels
Display aspect ratio : 2.40:1
Frame rate mode : Constant
Frame rate : 23.976 fps

When I play in the trimmer window it plays fine, but is really choppy in the preview window.

So I tried another –
Maximum bit rate : 1 051 Kbps
Width : 480 pixels
Height : 360 pixels
Display aspect ratio : 4:3
Frame rate mode : Constant
Frame rate : 25.000 fps

Same result – very choppy preview playback.

I find this odd as I do not remember having this problem when I last tried editing video a couple of years ago, and although a few years old now and probably no longer regarded as a high spec, my Acer laptop is no slouch.

Acer 8930
Win 8 64bit
2 hard drives. (300GB and 500GB)
6GB Ram
Intel P750 2.00GHz processor.

So something else is not right by the look of it but now I am completely baffled.

[Peter Herman]

Well now I am confused.

I found a number of internet site which tell me that the idea of a proxy is to create a much smaller file to work with to eliminate the choppiness experienced when editing high resolution videos on older computers.
For example listen to what is said at approx 5.15 in this video on this site
https://library.creativecow.net/articles/devis_andrew/Sony-Vegas-Pro_22/video-tutorial

The problem I have is that whether I use the original file or a there is a generated proxy the slow, and variable, frame rate I experience with even the lowest quality in the preview window is very bad (even with the GPU acceleration turned off) – and I am trying to find a way to fix the problem.

Any suggestions would be appreciated.