Video2DreamcastDisc is a complete suite of programs that can automagically convert any video file to a .iso file (which autoplays your video on the Sega Dreamcast) which can be burned and then booted with the Utopia Boot Disc.
How it works:
I've envisioned this program for months, and it's finally ready for release. Expect many improvements in future versions.
Excert from the website: https://alex-free.github.io/video2dreamcastdisc
Burn the Utopia CD Loader V1.2.cdi file in the Video2DreamcastDisc directory to a CD-R.
Drop the media file you want to play on the Sega Dreamcast on the vid2dcd.bat file in the release, a video.iso file will be generated. Burn the video.iso file with a CD-R writing program (like imgburn, cdrdao, cdrecord, etc.). do not use Windows Explorer.
Boot the Sega Dreamcast with the Utopia Boot Disc CD-R burned previously. Once the reindeer appears swap the Utopia CD Loader V1.2.cdi CD-R with the video.iso CD-R.
Close the lid, the video will autoplay. When done, turn the Sega Dreamcast off before removing the video.iso CD-R.