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Use PrefetchVirtualMemory() (if available) on memory-mapped input frames. Significantly improves performance when the source file is not already present in the OS page cache by asking the OS to bring in those pages from disk using large, concurrent I/O requests. Most beneficial on fast encoding settings. Up to 40% faster overall with --preset ultrafast, and up to 20% faster overall with --preset veryfast. This API was introduced in Windows 8, so call it conditionally. On older Windows systems the previous behavior remains unchanged.
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