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<p>Yes - although once you have seen a Key Frame, you can watch as
many (or as few) Deltas as you want. But you can't start midway
through.</p>
<p>If you want to be able to go backwards, you want to have lots of
key frames. If you have a Key Frame followed by 100 Deltas, you
cannot view the last Delta frame without finding the Key frame and
then constructing all the intermediate deltas.<br>
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<div class="moz-cite-prefix">On 06/08/19 20:47, pisymbol . wrote:<br>
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<blockquote type="cite"
cite="mid:CAPpy_fG3DQS1P=pOM3f-YSX+5uCLpivBMW-16R8fBMBGESEq2Q@mail.gmail.com">
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<div dir="ltr" class="gmail_attr">On Tue, Aug 6, 2019 at 4:51
AM Ian Davidson <<a
href="mailto:id012c3076@blueyonder.co.uk"
moz-do-not-send="true">id012c3076@blueyonder.co.uk</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">You asked "What is a Key
Frame?"<br>
<br>
If you think of a typical TV picture, much of the image
stays the same <br>
from one frame to another. You could create your video file
by storing <br>
each frame in its entirety - but in order to reduce the
overall file <br>
size we use 'Key Frames' and 'Delta Frames'. The Key Frame
has all the <br>
pixels required to make up the picture - just like a still
photo. That <br>
key frame will then be followed by a series of Delta Frames
which simply <br>
note the differences from the previous frame. If your video
is of a <br>
news reader reading the news, the delta frames would detail
the mouth <br>
moving and not much more. If you were to try to pick up
your video in <br>
the middle, you would have the detail of the mouth moving -
but you <br>
would know nothing about the news reader's face. Therefore,
you need to <br>
include Key Frames from time to time to enable starting
'part-way through'.<br>
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<div>Ian, isn't the Key Frame also the start of what is known
as a Group of Pictures (which is a complete set of Key and
Delta frames)?</div>
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<div>-aps<br>
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