Digital Video Compression Methods Part 3
Compression rules
You don’t need to know all the intricacies of the compression process if you follow these general rules of thumb:
If compression isn’t absolutely necessary, don’t use it! Until the editing and design of the material is completed, it is better to work with the original source to have a sufficient quality margin and compress it only at the last stage, that is, immediately before the output to the medium.
If compression is unavoidable, try to use the lowest possible compression ratio. In other words, always use the highest possible bit rate.
Do not turn on the compression systems one after the other and, if possible, avoid compression. This always leads to a loss of quality, and the lower the flow rate, the more pronounced this deterioration will be. The quality will be even worse if between applying the codecs you perform some editing actions or apply special effects.
Digital encoding systems always introduce a time delay and complicate video editing, and the use of compression can lead to desynchronization of audio and video streams.
Any compression system works best with the purest video footage. Signal noise, jitter, graininess and poor lighting when shooting, as well as poor decoding of the original video signal make compression difficult and produce poor results.
Compressed data is always much more susceptible to transmission errors than uncompressed data.
Do not believe the claims of manufacturers comparing codec quality to analog video (“VHS quality”, “quality comparable to Betacam SP”, etc.), because the defects of a compressed digital image are different from those of a Analog video, even if Analog video is played from a consumer VCR known for its defects.
The quality of the image obtained by this or that codec depends directly on the type and condition of the source material. Therefore, question even the most compelling demos, as you can use specially selected material to ensure that a particular codec works perfectly. Always use your own material for testing, selected based on a reasonable balance of “easy” and “hard” stories.
The quality of compression can only be assessed subjectively.
Many types of digital video compression are based on the fact that high-amplitude signals do not occur simultaneously at all frequencies, and when compressing audio signals, it is necessary to perform a frequency analysis of the input signal to develop a masking effect. . Spectral transformations are typically used for such purposes, which are also used in the phase correlation method to measure motion. A special case of spectral transformations are Fourier transforms, which are used in most of the known compression algorithms for audio and video signals. Fourier transforms are a processing technique used to analyze changes in signals over time and express them as a spectrum.
