I have a PDF with a short video embedded, but I’m not sure whether it will play on my phone. Does mobile support that, or will it just show a blank space?
Honestly, most default mobile readers won’t play it and just show a blank space. The simplest fix is opening it in the Adobe Acrobat app, but embedded video on phones is pretty hit or miss in my experince.
It depends on the PDF viewer. Mobile browsers and many phone preview apps do not play embedded PDF video, so you may see a blank area or poster image. I would test it in Adobe Acrobat Reader on both iPhone and Android, and provide a normal video link as a fallback.