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Jumping backward with digital TV framing is naturally a hit or miss occurrence.

Your digital TV/satellite receiver "creates" 30 full frames per second out of the digital signal that it receives.

Each of those frames is "built" from data from a variable number of previous frames - only pixels on the screen that have changed are updated in the new frame.

A digital TV picture consists of several different types of frames.

Occasionally a complete frame is sent, I believe they call these an "I" frame.

Between "I" frames will be frames that are pieces of the previous "I" frame, that only contain pixels that have changed since the last "I" frame.

You can readily see how if it is a relatively long time between "I" frames, it causes a problem for jumping backward since that jump MUST be to a previous "I" frame to get a complete screen shot - how many "I" frames back does the DVR jump, if you set a static number in programming, then you run the risk if jumping randomly backward (the problem Dish receivers have) and if you some how use a time base backward jump it exponentially complicates the calculations the DVR must make to hit the approximate time target.

I believe TiVo has the patent on the best way to run digital fast forward and rewind and even though Dish and TiVo have kissed and made up, Dish is not using the TiVo method for FF and REW, they may not be allowed to by their agreement with TiVo - I don't know.

Rewind on a digital TV picture is an extremely complicated process, not just as simple as it once was with a VCR where it just read the analog data backwards and displayed enough of it to almost make an intelligible screen - digital moving pictures are layers and layers of what changed, what did not and what's the median between the two.
 
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