i was investigating how much the GOP-setting in the export setting (advanced - video) matters in respect to resulting file size. I tried 15, 30, 60, 120, 300 and 900 GOP. The decrease in file size from 15 to 30 or 30 to 60 is about 4…5% (in my case). From 60 to 120 its around 4% and from 120 to 300 less than 3%. From 300 to 900 its only around 1% or less.
From the visual result to my eyes i hardly could see any difference and i tried several quality settings as well. Reduction in quality pays much more to size reduction than GOP but also starts to insert visual artefacts below around 50.
What are reasonable values for the GOP setting? I would guess 15…60, or in some cases even 300 but it probably makes any later edits more difficult resulting in additional artefacts when GOP increases much. Is my understanding roughly correct?