Hmm, indeed, the weight has increased a bit in the earlier works, which were well optimized without conversion. The resolution was set to 1280 horizontally, 1080 vertically. What codec are you talking about, and what weight gain does it give? I used the following parameters for ffmpeg:
ffmpeg.exe -y -i "%%i" -r 60 -c:a aac -b:a:0 320k -c:s copy -c:v libx264 -preset slow -tune animation -b:v 20000K -crf 18 -vf "scale='min(1280,iw)':'min(1080,ih)':force_original_aspect_ratio=decrease,pad=width=ceil(iw/2)*2:height=ceil(ih/2)*2" "%%~pi%%~ni.mkv"
Unfortunately, I no longer have the original files, they were all taken from this thread.