Explanation of Interpolation

Could someone tell me the significance of Interpolation in the Settings menu? Does the choice of interpolation only determine image quality in the monitor window purely for editing performance purposes, such as the situation where you might set it to a lower quality choice because your computer may not be quite good enough for realtime playback of UHD footage? Or, does it actually have an effect on output image quality for exports?

The Settings menu item is only for the monitor window. When it comes to final export, there is another interpolation option on the Export > Advanced > Video tab.

There is one nuance to the Settings menu item… if it is nearest neighbor, then frame-accurate seeking is not guaranteed depending on the encoding of the source video. Use bilinear or higher to get frame-accurate seeks while previewing the timeline.

For final export, a number of people choose bicubic for downscaling and Lanczos for upscaling. Lanczos may be the superior downscaler for still images, but it can produce ringing artefacts that are noticeable during panned video, especially at resolutions lower than 1080p. It’s something to test for and be aware of.

Many thanks for a very full answer.

This is in the docs:

This no longer applies as of version 19.08. It always strives for frame accuracy now except for trick play modes: reverse, rewind, and fast forward (does not apply to Properties > Speed).

Thanks for correcting me. I read the release notes of every version but I guess I missed that item. Sorry to provide out-of-date information.

Thanks for the extra information. I am using the latest version of Shotcut (so convenient to use AppImage to always keep up to date), so presumably setting a lower interpolation scheme would now present no problems for frame accurate working. I originally asked this question because I am editing UHD video and my machine may not be quite up to it. What happens in Shotcut when playing the timeline is, on approaching an edit point (just a simple cut, not a transition), there is always a brief freeze on the outgoing shot, before going into the next one. This happens on every edit point, and I assume relates to the performance of my machine, and that is why I was interested in setting a lower interpolation choice.

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