@AbdelhadiAfa The only way I know of using proxies independently of preview resolution is to put all your media in a single folder and make proxies manually and then put them in a different folder. Then you can use Swap Video Files in Project Media to switch between the 2 folders, if all the file names match. I think the 3rd Party HOS apps have a menu driven feature to automate the process. Whichever way you do it, this gives you the opportunity to make HD clips for your proxies of 4k media which will work better with masking and chroma-key than 720 media. Works best if frame rates match or are at least even divisors of the original. The bonus is that this approach yields higher performance when editing with proxies compared to Vegas default proxies which change both the frame rate and res by an irregular amount and then make up for it with time-stretching. Downside is you have to manually switch folders back to get the better quality render with original media... although there is a render option in vp23 that makes swapping the folder back more convenient.