How to Custom Thumbnail | Add Thumbnail to Videos like MP4 MOV M4V on Windows 10 macOS Big Sur

It is really a pity that such a free and useful program no longer working, and I am looking for an alternative, only to find no similar programs available. However, in this post, I am bringing good news for you as you can custom thumbnail yourself with Wondershare UniConverter. I mean you can add a picture as a thumbnail or cover art of your videos like MP4, MOV, and M4V on Windows and macOS. Here is a detailed guide on how we can do so.