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After you hit OK to load the shot, the image prefetch system begins to bring it into your processor’s RAM for quick access. You can use the playbar and timebar to play and scrub through the shot.
Image prefetch puts a severe load on your processor by design—it rushes to load everything as fast as possible, taking advantage of high-throughput devices such as RAID disks. However, if the footage is located on a low-bandwidth remote drive, prefetch may cause your machine to be temporarily unresponsive as the operating system tries to acquire the data, or even your network drive system to misbehave.
Also, if you are scrubbing in an uncached shot, prefetch can cause the user interface to become less responsive, as it must finish reading and processing frames that it has already started.
SynthEyes gives you a variety of controls over performance that can be adjusted based on the type of source and size of the shot compared to the cache RAM.
First, the “Read 1f at a time” option on the Shot menu ensures that SynthEyes only tries to read a single frame at a time, greatly reducing read performance. This is on by default, to prevent poor network disk systems from having trouble, but you’ll be asked if you want to turn it off, which is usually the case. (It is a sticky preference from run to run.)
More subtly, you can adjust “Frames in flight” in the image preprocessor section.
Frames in flight encompasses reading the file from disk, uncompressing it, and doing any image preprocessing you’ve set up in SynthEyes. If you have lots of memory and a fast RAID or SSD drive, this value can be larger, but be aware that it can reduce responsiveness if you try to scrub a shot that doesn’t fit in RAM.
You can also reduce “Reads in flight”, which encompasses only reading the file and uncompressing it. Use this to prevent your disk system from getting overloaded with too many requests if it isn’t SSD. By reducing only this value, and not Frames in Flight, you can keep a regulard hard disk focussed, while leaving plenty of threads to perform extensive image preprocessing. (The same threads read and process, so Reads in flight is effectively limited to at most Frames in flight.)
NOTE : Frames in flight and Reads in flight were added in SynthEyes 2006. To match the behavior of earlier versions, set both values to zero, which causes the number of CPU threads in your system to be used… which can be quite (over) large on big machines.
ARRI and BRAW file readers have their own Frames in flight settings that can be used to further reduce the overall Frames in Flight value: those frames can be very large and the decoders can use many system resources.
You also have the option to turn off prefetch on the Shot menu, or turn off the prefetch preference (in the Image Input section) to turn prefetch off automatically each startup.
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