App which makes video quality better with less size

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thats not how upscaling works 

if you have anything below 720p it cant be improved upon

only 1080p and after you can improve a footage 

1080p upscaled to 2k or 4k there is a little bit improvement in quality 3% to 9%

these tools just mak it so that humans are fooled the actual quality never improves its all about how realistic it is to your eyes

anytime a native 4k will be superior

1080p videos dont really take advantage from better formats like h265

anything above 1080p does save a lot of space with these formats so inshort even if you upscale that video to 1080p whatever the output is cant be reduced 

for example a 90mb video file is upscaled to 1080p and the output is 300mb even if you convert it to h265 you will only save 5 to 9mb 

using ai you can but that requires a lot of resources and the output loses its reality 

Not sure that's possible. The best you can do is use video compression apps/softwares that can reduce the file size without compromising the original quality. I don't think any program exists that can enhance the video quality and at the same time decrease the file size.