i select a page in theme option to be the default single portfolio page.
Now i would like to make a second portfolio page with different link of video.
The problem is that, when i add a new portfolio entry for my second page, the entry appear in the single default page. So how can i select the page for my portfolio entry.
You will need to use shortcodes to filter out the portfolio entries. Pls have a look at the [show_post_snippets] shortcode in documentation. Basically you assign portfolio items to different categories and then display the desired portfolio entries by filtering via taxonomy and terms param supplied to the above shortcode.