Not OP, but have a look at [0]. It’s not great, but good enough. I regularly use it for App Store screenshots with captions and text. [0] https://theapplaunchpad.com/. - Source: Hacker News / about 1 year ago

For an advanced approach that includes localizations of your text and a ton of included resources to build your designs off of, there is AppLaunchPad (which has both a screenshot version and a mockup version with free and pay-by-the-month options), there is Vernissage which has a free and a pretty cheap pro version, and then there's App-Mockup which is free web-app. Source: almost 2 years ago

I used this. Paid for one month and got a good use out of it. https://theapplaunchpad.com. Source: over 2 years ago

I used AppLaunchPad. It’s a paid service but you can go monthly for single months when you need it (US$ 29). And you can easily wrap device frames for different size and colors of iPhone and iPad around the standard screenshots that you supply. Source: almost 3 years ago

2) Get your video you want as your wallpaper and go here, you can upload it to a video storage/sharing site. (Make sure to crop this video to your monitor dimensions). Source: over 2 years ago