Filter Plugin Frontend set String Parameter for Framerate

Hi All,
First of all many thanks to the Developer(s) and Contributor(s) of shotcut, this is a great opensource project.

I have been trying to create a frontend for an existing mltservice filter and have problems on setting the value of a parameter that is supposed to be a string.

Specifically I have been trying to create a frontend for the following filters.
[ avfilter.framerate ] (

Both have the parameter
‘av.fps’ which is of type string

in the ui.qml file I have tried setting the value directly with integers strings but no success in influencing the behaviour of the filter or resulting in a shotcut crash.
filter.set(‘av.fps’, 15)
filter.set(‘av.fps’, ‘15’)
filter.set(‘av.fps’, “15”)

I had previously attempted to use the fuction .toString() to get a string value from a Slider value but in an attempt to figure out where I was going wrong I resorted to directly setting static values.

Acording to my research: this is a string which can be a whole number such as “30” or a rational number such as “30000/1001”

I have been trying to simplify as much as possible my qml files to be able to test, although it seemed to do something previously (actually slowing down the video), lately with simply including the filter in the mlt_service definition, shotcut crashes as soon as I add the filter.

I thought that I was having trouble in setting a string variable, but I am starting to think that perhaps shotcut is not capable of integrating these specific filters yet.

Any feedback would be apreciated, Thanks.

That avfilter will not work properly in MLT because it tries to adjust frame rate, but MLT is in control of that. It should have been blacklisted, but libavfilters keep getting added without the blacklist updated.

Thanks for the reply :slight_smile: and confirmation. Is there a way of adjusting linearly the framerate of a clip?

I know that the framerate of a whole clip can be adjusted, but I would like to emulate a slow/fast motion at specific positions in the clip.


OK, sorry for the redudant question, found the reference to another Post describing the keyframed speed Suggestion which is has already been taken into account.

Slowmotion with keyframes?

Just as reference, I currently use SlomoVideo to do my slowmotions. it builds well on ubuntu, on windows I have not been able to build the project, so I have started scanning through the code a bit and was thinking of possibly guiding my efforts towards incorporating a variant of it into shotcut if possible.

I have thought about the same thing… eventually. So much to do though.

1 Like

This topic was automatically closed after 90 days. New replies are no longer allowed.