Be patient since I haven't worked with compression algorithms much so this may be obvious to some of you. Something I've always noticed when some streaming video starts to lag. I only realized I was curious when looking over this question:
Twitter image encoding challenge
I'm not talking about the pixels themselves but rather the grid like layout that results from the compression. What sort of algorithm or technique is this indicative of? What can you tell me about it?
Take a look at this Wikipedia article on MPEG-2. To quote a part of it:
Briefly, the raw frame is divided into 8 pixel by 8 pixel blocks. The data in each block is transformed by a discrete cosine transform. The result is an 8 by 8 matrix of coefficients. The transform converts spatial variations into frequency variations, but it does not change the information in the block; the original block can be recreated exactly by applying the inverse cosine transform.
In other words, the grid-like structure you see is a direct effect of this DCT being applied to the 8x8 blocks of pixels.