My video isn't autoplaying on mobile
If your video isn't autoplaying on mobile, it's most likely caused because it doesn't have enough battery, or you have the Low-power mode enabled on your device. The low-power capabilities of mobile devices are managed by the device operating system and it is not something that we can override. Mobile devices stop video autoplaying when the battery is low and they do not allow websites to change that. You can read about that in this article https://archetypethemes.co/blogs/support/why-wont-my-videos-autoplay
Also, for iOS devices specifically, you might want to check this Apple document: https://support.apple.com/en-us/HT205234, which explains that when a device has this feature (low-power mode) enabled, it reduces and affects features like automatic download or some visual effects.
However, please note that the user still can play videos by clicking on a 'Play' button. You can show a 'Play' button on the video by enabling the following feature on the app preferences page.
Finally, you may want to check My video autoplays but sound is not working, which explains what's the expected behavior for video autoplay and sound on different Browsers.