Knowledge Base Article
Article Type: How To
Product: Symphony
Product Version:
Component: Symphony Server
Device Brands:
Created: 18-Oct-2011 4:53:21 PM
Last Updated:

How are footage files written to the NAS

Solution

  • Footage files are written to disk using an OS blocking write call
  • Symphony writes frames in chunks (multiple frames at a time) where the chunking size is optimized for the stream/hardware.
  • The frame sizes vary depending on CODEC, settings, resolution, and whether we are writing difference frames or key frames
  • Frame size can vary widely
    • ~5KB/frame (H.264 P or B frames at standard definition)
    • ~500KB/frame (MJPEG HD camera)
  • Symphony uses NTFS
  • To tweak performance you can set the following variables in Server Manual Configuration Editor:
    • Type: Global
    • ID: <empty string>
    • Section: Main
    • Key: FootageBufferBytes
    • Value: 65536

NOTE: Value is 65536 by default. We recommend a power of two, ideally matching or exceeding your disk's allocation unit size.

  • Type: Global
  • ID: <empty string>
  • Section: Main
  • Key: FootageBufferAutoGrow
  • Value: 1

NOTE: Value is 1 by default. If it is anything other than 0, Symphony automatically increases the buffer you specified above to ensure it holds at least two key frames.

  • Footage files are created with the filename as the UTC time at the start of the video
  • Symphony rolls over to a new footage file when it becomes 3.75GB or 6 hours has elapsed (whichever comes first)
  • To force the footage buffer to start at a size other than 64K set the FootageBufferBytes variable
  • To stop the buffer from automatically increasing set FootageBufferAutoGrow to 0

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