In article ,
John Walliker wrote:
On Tuesday, 9 February 2021 at 12:54:27 UTC, JohnP wrote:
I am not sure, but I THOUGHT that the replay head moved along with
the film, in jerks...

The sound head is a distance away from the fim gate and the head is
where the film is moving steadily through a capstan. There is a loop
in the film to absorb the jerking.
BBC Research Dept produced a progressive scan digital telecine machine
in the early 1970s which moved the film in a continuous motion
everywhere. There was a CCD line sensor feeding a digital field store to
generate an interlaced signal.

Yes - you could run it up from a still frame. Rank made a commercial
version. Only snag being the sound still took several seconds to become
stable.

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*The severity of the itch is proportional to the reach *

Dave Plowman London SW
To e-mail, change noise into sound.