[Cin] ReframeRT, Interpolate Video

Andrea paz gamberucci.andrea at gmail.com
Thu Jan 3 11:16:08 CET 2019

That's all I know about the Interpolate Video plugin. If someone can
complete and correct it does me a great favor.

Interpolate Video


Each video has its own framerate. If we want to change it (for
timelapse or slowmotion) the best thing is to shoot the scene with
suitable framerate. But even in post production we can do something.
The simplest method is to remove some frames to speed up the movie or
add some to slow it down (from now on, for simplicity we will consider
only the timelapse). Needless to say, the result is not smooth and the
viewer will notice it immediately. A better method is to use the
interpolaion, mediating the pairs of frames that alternate. For
example, if we have a sequence of frames 1, 2, 3, 4, 5, 6, 7, 8… we
can make a timelapse mixing frames 1 and 2, 3 and 4, 5 and 6, 7 and 8
and so on. So we will have a new sequence of 4 frames instead of the
initial 8: 12, 34, 56, 78… We will get 50% acceleration but it will
always be of bad quality because of the too rough blending between the
pairs of frames. Blending can be improved by weighing it differently
by 50% frame 2 + 50% frame 2, but the result is still unsatisfactory.
Further improvements can be achieved by using logarithmic or
exponential interpolation instead of linear interpolation. But the
most sophisticated methods that lead to better results are based on
optical flow analysis. These analyse the movement of circumscribed
areas over a given period of time. With this method the intermediate
frames do not derive from an approximate blending, but from the
calculation of the vector of the motion between two frames that
determines the displacement (warping) of the moving figure in the new
intermediate frame.

Interpolate Video works this way.


The interpolate effect tries to create the illusion of a higher frame
rate from source footage of very low framerates by averaging frames
over time. It averages two input frames for each output frame.

The input frames are at different times, resulting in a dissolve for
all output frames between the input frames. You choose a zone to be
evaluated (macroblock size) and a radius (search radius) where you can
search for this macroblock in the following frames. The Use optic flow
button is activated and playback starts. The plugin will calculate the
motion vector (which can be made visible by the draw motion vectors
button) and apply it to intermediate frames. Tutta l’operazione
risulta estremamente pesante sul sistema. [Once the analysis is done,
we can scroll the video by unchecking the two buttons and obtaining
the desired result] (This last part is not certain at all). There are
two ways of specifying the input frames. You can specify an input
frame rate which is lower than the project frame rate. This causes
input frames to be taken at even intervals. (how do I choose input
frames? Random?Are better low numbers or hight numbers)? You can also
specify keyframe locations as the positions of the input frames. In
this mode the output frame rate is used as the input frame rate and
you just create keyframes wherever you want to specify an input frame.


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