Introduction

The VC-2 standard defines the video decoding process using infinite precision integer arithmetic. For practical implementations, however, fixed-width integers must be used to achieve useful performance.

If a codec is built with too few bits of precision, artefacts may be produced in the event of integer wrap-around or saturation (see examples below). If too many bits are used, however, the implementation will consume more resources than necessary.

Perhaps surprisingly, the question ‘how many bits do I need?’ is not a simple one to answer. This software attempts to provide useful estimates for these figures based on mathematical analyses of VC-2’s filters

Before introducing this software it is important to understand its limitations and the terminology it uses. These will be introduced in the next few sections before the command line and Python library interfaces of vc2_bit_widths is introduced.

Contents:

• Caveats
  • Assumed encoder behaviour
  • Non-linearity
• Terminology
  • Levels and subbands
  • Intermediate value arrays
  • Phases
  • Targets