I found a solution! Thank you MofX for right direction!
Geometry newSize = Geometry(m_newSize.width(), m_newSize.height());
newSize.aspect(true);
list<Image> frames;
readImages(&frames, imagePath.toStdString());
for (auto& image : frames)
image.resize(newSize);
writeImages(frames.begin(), frames.end(), newImagePath.toStdString());