What you are seeing could be a few things... . but I'll explore the most likely scenario in this post.
With any digital system, you have A/D (analog/digital) converters... . or codecs (Compression / Decompression). The codec's sole purpose in life is to reduce bandwidth so that the signal can be passed or stored as efficiently as possible. The codec (whether through software, hardware, or both... ) looks at the digitally sampled information and through a complex algorithm, it decides which information will be excluded from the final stored/transmitted signal. It will fill in the missing pieces that it deemed a redundancy and sometimes you see the end result in the form of 'motion blur'... or you'll end up with perfect little boxes all over the screen... . That's the codec being overwhelmed with too much bandwidth...
There are a lot of points along the video/audio stream where this compression/decompression is happening... so there are a lot of chances for this sort of dropout...
Completely analog systems are not prone to this as the signal is stored and transmitted as an electrical waveform. Since an analog signal is an electrical waveform... it is highly susceptible to interference... . this is part of the reason why digital signals appear so clean... they are not as prone to interference... . or what I should say is that they have error correction and an "all or nothing" signal transmission sceme. You either got it... or you don't... . there's nothing inbetween... . like static in an analog system.
Make sense?
The difference between digital and analog is pretty significant. This post is getting too long, so I'll explain it further if you'd like in another post... .
Matt - video geek