How to remix (almost) any YouTube video into a Short or restrict access to your own videos
YouTube allows anyone to create Shorts from any long-form videos on the platform, with a few small exceptions.
You may have spotted the 
Create button below many YouTube videos via the mobile app. Nearly all videos are now opted in by default to allow anyone to record a Short using the audio. That being said there are a few exceptions and creators can choose to opt their channel’s long-form videos or specific long-form videos out.
Music videos uploaded by YouTube’s music partners are ineligible to be remixed by default. Unfortunately, content uploaded to YouTube Shorts cannot be opted out of sampling, meaning when you upload a video to Shorts, you are consenting to have other’s remix your videos. Other platforms like TikTok allow you to restrict your audio in this way. It would be nice to see YouTube give creators who want this feature the option, going forward.
How to sample the audio of (almost) any video on YouTube
- Find your chosen video and tap Create.
- Slide the waveform to choose the audio’s start point, then tap Done.
- Record and edit your Short.
How to sample audio from an existing Short
- Find your chosen Short and tap the
wave icon in the bottom right corner. - Tap
Use this sound. - Record and edit your Short.
How to restrict my videos from being sampled
- Head to YouTube Studio on desktop
- Click Content on the left menu
- Click the title or thumbnail to edit the video details
- Scroll down and click SHOW MORE
- Untick the box labelled Allow people to sample this content
- Click SAVE in the top left corner
YouTube have also detailed how to change your Short sampling preferences in bulk or when you upload.