Well, ..., back in the day (actually it wasn't that long ago) TV was transmitted via Analog signals over the airwaves. It was smooth, no pixelation, not very high in definition, but very reliable. Then things got complicated. Cable companies started using up all the avail able bandwidth in VHF. There was no way to transmit high def TV without consuming 2 VHF Channels at once. Moreover, cable companies moved quickly into UHF realm. They created the cable converter box to convert UHF signals to signals that could be used by the VHF dial on your TV.
Measures were already under way for revamping TV bandwidth when 911 hit. Sept 11, 2001 demonstrated that our fire, rescue, and police couldn't talk to one another on their radios. This exacerbated the already horrible confusion surrounding the terrorist attacks to such an extent that the FED were, well fed-up. So they set a mandate of 2009/2010 to change the allocation of bandwidth in the United States. So, in 2010 all TV stations (if they wanted to remain on the air) were forced into a higher frequency UHF bandwidth and were forced to convert over to digital formats. Supposedly Emergency services go the VHF bandwidth that was once used for TV.
Now, most older aerials could still pickup the UHF digital TV signal but you needed a box to convert the digital signal back to analog so that older legacy TV sets could view the program being aired. However, since it is a digital signal now comes to us in chunks, that we call "packets", of information.
So in the old days when the analog signal messed up you lost your horizontal or vertical sync (sometimes both) and the picture would scroll up down, sideways, or diagonally. Or you'd loose signal and get a snowy picture or the sound would mess up. Of course you had controls like the vertical and horizontal controls to help you correct the loss of signal. Today, since a computer is now processing packets of incoming information, we need to receive packets in a continuous uninterrupted stream in-order to watch continuous TV images. If something goes wrong, the TV (if the processor is fast and packet buffer deep enough) can wait a little for bad packets to be retransmitted of in some cases can correct errors in the packets themselves. But when that fails the TV set earps a-bit; vomiting the un-used and partially received packets all over the front of your TV screen (we call this flushing the queue) causing the "pixelation" (or blocky pattern) that we all know and love. Then it waits to receive and assemble more data packets into a use-able picture, fill up it's receiving buffer (or queue), and begin delivering continuous pictures to your set. During that time period the set may appear to freeze but really the set (or converter box) is collecting data to be displayed once more in a continuous picture.
However, in some cases, the operating system (internal to the TV set) may lock up and will "freeze" the picture in the blocky pixelated mode you described. When this occurs the set may freeze permanently (until you power it off and then back on) or it may quietly restart itself.
OK, that's probably more than you wanted to know about it but unfortunately it's here to stay. Welcome to the digital age of TV!