For example, if I was on a rocket to mars and transmitting a video stream back to earth non-stop for the duration of the journey…
At the begining when I am leaving earth, the lag between me transmitting the video and earth recieving it would be basically nothing. But by the time I get to mars there is a delay of 3 minutes or whatever between send and recieve.
What happens to the video during the journey? Do some frames randomly drop? Does the video have to buffer constantly? Is there an incremental decrease in quality over time?
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The people on the ground would be watching a slightly slowed down version of the feed.
To illustrate why, suppose a spacecraft transmits video in pulses, i.e. it sends a frame worth of data every 24th of a second or whatever. It’s a model example that’s sufficient to demonstrate the idea
Each pulse has to travel slightly further than the one before, which means the time gap between consecutive frames sent is that 24th of a second gap *plus* the time it takes the pulse to travel the distance the spacecraft moved in that 24th of a second gap.
All of this means while the spacecraft sends out frames every 24th of a second, ground control *receives* those frames slightly more spaced out, which means the footage is received and played back at a slightly slower framerate. The discrepancy is tiny, because light is fast and spacecraft are slow, but its there.
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