The resolution of the videos depends on the quality of the phone camera (or the resolutions of the videos / photos that would have been imported without being filmed directly via the Kannelle application).
If an old phone does not allow High Definition (HD), then Kannelle will not be able to produce HD videos (unless all the footage is imported in HD from the photo / video file library).
Finally, if you are making a video project with footage of varying resolutions, then we homogenize the resolutions upwards within the limit of 1920 pixels wide and 1080 pixels high (for a landscape video). Indeed, we do not harmonize the dimensions of videos up to 4k because we have found that most of the videos were used for distribution on social networks, where 90% of the audience views them on smartphones. It would therefore be a too important dimensioning increasing the weight of your videos without any visible benefit for your audience.