user9115: (Apologies if this is the wrong stackexchange, it seems the most appropriate)
When rewinding a VHS tape on an analog player (i.e. a VCR hooked up to a (CRT?) TV) when rewinding, or fast-forwarding, and regardless of video format (NTSC vs PAL vs SECAM) we're always treated to the same effect: a relatively clear window into the video playing backwards (or forwards), overlayed with two or three bars of static. I found a good example on YouTube here (around the 00:06 - 00:10 time): 


What causes this? How does the action of the helical-scan tape over the read head cause these artifacts?
I also wonderred: when rewinding, if the VHS tape is playing backwards, and the video signal is scanned one scanline-at-a-time, how is it the video display is not vertically and horizontally inverted? Even on early, pure-analog VHS players lacked framebuffers yet when rewinding their displayed the video in the correct orientation, how was that possible?

user3908: In helical-scan video players, the tape is wrapped around a rotating drum that has one or more magnetic pickups (heads) that are the width of a track and angled slightly from true horizontal. Each track is several inches long and laid down diagonally at (roughly) the same angle as the head is tilted. (The angles differ because the relative motion of the tape and heads causes a precession, an "active angle").
When the tape is moving forward at normal speed, the rotating head aligns with the angled tracks and all is fine. When the tape moves in reverse the angles are misaligned, and when the motion is faster than normal the heads will "sample" more than one track during a video frame, and pick up some of the inter-track guard space as well (the static). 
This is what you see when you rewind. Nothing about the orientation of the data on tape changes, so there's no reason for the images to be inverted. If the drum rotated in a different direction then you'd see something else.


9115: <p>(Apologies if this is the wrong stackexchange, it seems the most appropriate)</p>

<p>When rewinding a VHS tape on an analog player (i.e. a VCR hooked up to a (CRT?) TV) when rewinding, or fast-forwarding, and regardless of video format (NTSC vs PAL vs SECAM) we're always treated to the same effect: a relatively clear window into the video playing backwards (or forwards), overlayed with two or three bars of static. I found a good example on YouTube here (around the 00:06 - 00:10 time): <div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/QnkWzu4OGjI?start=0"></iframe>
            </div></div> </p>

<p>What causes this? How does the action of the helical-scan tape over the read head cause these artifacts?</p>

<p>I also wonderred: when rewinding, if the VHS tape is playing backwards, and the video signal is scanned one scanline-at-a-time, how is it the video display is not vertically and horizontally inverted? Even on early, pure-analog VHS players lacked framebuffers yet when rewinding their displayed the video in the correct orientation, how was that possible?</p>
 3908: <p>In helical-scan video players, the tape is wrapped around a rotating drum that has one or more magnetic pickups (heads) that are the width of a track and angled slightly from true horizontal. Each track is several inches long and laid down diagonally at (roughly) the same angle as the head is tilted. (The angles differ because the relative motion of the tape and heads causes a precession, an "active angle").</p>

<p>When the tape is moving forward at normal speed, the rotating head aligns with the angled tracks and all is fine. When the tape moves in reverse the angles are misaligned, and when the motion is faster than normal the heads will "sample" more than one track during a video frame, and pick up some of the inter-track guard space as well (the static). </p>

<p>This is what you see when you rewind. Nothing about the orientation of the data on tape changes, so there's no reason for the images to be inverted. If the <em>drum</em> rotated in a different direction then you'd see something else.</p>

<p><a href="https://i.stack.imgur.com/z9MGB.jpg"><img src="https://i.stack.imgur.com/z9MGB.jpg" alt="an image from the Wikipedia page for VHS"></a></p>
