9 Control

Video processing algorithms frequently offer - or require - some form of external control, which is for our purpose simply defined as being any kind of non-video data. VYA distinguishes between four types of control parameters:

• constants
  • defined in the code at compile time
  • cannot change unless the code is modified and re-compiled
  • examples: VYA_MIN_BITS, VYA_MAX_BITS_S, VYA_MAX_BITS_U
• parameters
  • defined as arguments in the constructor of a process (network) at instantiation time
  • cannot change during an instantiation of a process (network)
  • example: bitPrec
• deterministic tokens
  • defined through input ports of a process (network) at run time
  • used to control the data flow between modules, e.g. the amount of data consumed and/or produced, or the routing of data
  • may change during an instantiation of a process (network), but must be synchronized with tokens that control modules with which the module in question interacts; improper synchronization would lead to incorrect system behavior
  • example: lineLen, imgWidth, imgHeight
• non-deterministic tokens
  • defined through input ports of a process (network) at run time
  • used to control the data contents rather than the data flow
  • may change at any moment during an instantiation of a process (network) without affecting proper behavior of the module
  • reading is conditioned by YAPI's select function [1]
  • example: filterCoefficients