Disk Space Preallocation for the Capture File
Preallocating disk space for the capture file builds a file of a specified
size on the disk before the start of a capture operation. Preallocating a capture
file reduces the processing required while capture is in progress and results
in fewer dropped frames. You can preallocate a capture file by using the WM_CAP_FILE_ALLOCATE
message (or the capFileAlloc
Typically, your application should preallocate enough disk space to contain
the largest capture file anticipated. Preallocating disk space does not restrict
the size of the captured file. The file size is automatically enlarged if the
captured data exceeds the allocated space. Subsequent write operations to the
capture file reuse the portions of disk space allocated for the file, preserving
the size and fragmentation of the file.
You can also improve capture performance by defragmenting the capture file. To
defragment the file, use a defragmentation utility such as Disk Defragmenter.
If you use a defragmented capture file and later enlarge it, you should
defragment the enlarged file. Enlarging a defragmented capture file can fragment the
expanded portion of the file and reduce performance in the capture operation.
You might also improve performance by using an uncompressed disk for video
capture. Compressing data during capture can limit capture throughput to the disk.
An application can reserve a permanent capture file to eliminate the time
required to preallocate and defragment a file each time it is started. Because a
capture file can require considerable disk space, and preallocating a capture
file removes all data from an existing capture file, an application should let the
user decide if the file is permanent or temporary.
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