How do I reduce frames with blending in ffmpeg

Question

I am trying to convert some files into ProRes. One fairly important part of the conversion is:

• reducing frames from 60 to 30
• blending every 2 frames

Answer 1

Simple frame dropping:

ffmpeg -i input.mov -r 30 output.mov

Interpolate frames with the minterpolate filter:

ffmpeg -i input.mov -vf minterpolate=fps=30 output.mov

• See link above as there are many additional options.

Interpolate frames with the framerate filter:

ffmpeg -i input.mov -vf framerate=fps=30 output.mov

• See link above as there are many additional options.

Answer 2

Try

ffmpeg -h

or

ffmpeg --help

and you'll have a short help. Please read it. :)

Try

ffmpeg -filters

and you'll have a list of available filters

Try

ffmpeg -help filter=name

and you'll have syntax and parameters for this filter

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I already needed to do something like this, reducing framerate. If you do

ffmpeg -i "input" -r outputframerate [video encoding options...] [-y] "output"

Note : Things in brackets [] are optionnal.

You'll have a simple framerate change, with a possible loss of input frames. And, it's especially what you don't want to get.

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To have a framerate change without a loss of input frames, you'll have to use a video filter.

The tblend filter blends successive frames. It is the filter to use if source framerate is an integer multiply of destination framerate (eg : 60→30, 75→15, 75→25, ...)

ffmpeg -i "input" -vf tblend=all_mode=average [video encoding options...] -r outputframerate⁽¹⁾ [-y] "output"

⁽¹⁾ If haven't tested this filter myself, and I'm sure the output framerate must be set somewhere. The tblend filter has no fps parameter. Maybe it just blends 2 successive frames ? You should check this point, and make some tries ?

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There exists another framerate changer, more adapted to be used with any i/o framerates :

minterpolate : Frame rate conversion using Motion Interpolation.

So, type :

ffmpeg -i "input" -vf minterpolate=fps=outputframerate [video encoding options...] [-y] "output"

The other minterpolate parameters have good enough defaut values, to make sure a good blend. Check them with a

ffmpeg -help filter=minterpolate

If you want to add some parameters in the minterpolate chain, you'll have to use a ':' as parameter separator. Let's say you want to use motion interpolation mode = blend, instead of the default motion compensated interpolation (mci), type :

ffmpeg -i "input" -vf minterpolate=fps=outputframerate:mi_mode=blend [video encoding options...] [-y] "output"

If you want to use many videos filters, you must not chain -vf options. The last one will override the ones before. You must (as ':' for filter parameters) use ',' as filters separator. Ex :

ffmpeg -i "input" -vf minterpolate=fps=outputframerate:mi_mode=blend,filter2=param1=value1:param2=value2[...] [video encoding options...] [-y] "output"

The order of given filters are important.

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Things have been done with

ffmpeg version 3.2.14-1~deb9u1 Copyright (c) 2000-2019 the FFmpeg developers