Bizarrely, rendering performance in Sony Vegas Pro 8 suffers by a factor of 3 if the Dynamic RAM Preview is set to use 0MB. Increasing it to 1MB results in a 200% performance boost.

Dynamic RAM Preview normally allows you to render a small selected portion of your project to preview it smoothly. This is especially useful if you have a portion of your project that includes many transitions and effects: without this facility, you may be unable to preview it at a usable frame rate. You can increase the amount of RAM reserved for this task, which increases the length of clip that you can preview. Mike J has a good explanation on the Digital Media Net forums.

However, if you don’t use this feature, the recommendation is to reduce the RAM kept aside for it, allowing it to be used elsewhere. I hardly ever use it, so I reduced it to 0MB—a mistake, as I found out.

John Cline over on the Sony Creative Software forums has produced a handy “benchmark” file, rendertest-hdv.veg to compare the rendering performance of different systems. For instance, in 32-bit Vegas, a stock Core i7 920 could chomp through the rendering in about 1 minute 50 seconds. A lesser Core 2 Quad Q9400 could manage in about 2 minutes 10 seconds. By comparison, at first I was clocking in at over 10 minutes! Something wasn’t right. I downloaded Vegas Pro 8.1, which is the 64-bit version, and the file rendered in under 2 minutes 40 seconds.

I realised, after some playing around, that the Dynamic RAM preview setting was to blame. Strangely, if I increased it to 1MB, the rendering time improved tremendously, dropping to around the 2 minutes 55 seconds mark.

Simple then—if you’re using Vegas Pro 8.0c or 8.1, don’t set the “Dynamic RAM Preview max (MB)” setting to 0MB. A rather silly bug; it would have been good if Sony had picked up on it.