Inline embedded players go full screen when playing on mobile devices, especially on small screen devices like iPhones. This behavior can vary from device to device depending on operating system and screen size.
When comparing a playback on devices like iPhone vs Ipad the experience seems to be different sometimes between websites as well.
As per design some mobile devices restrict inline playback to optimize user experience. This cannot be controlled directly by the player or the browser as it is embedded within the device functionality itself.
Information from developer available here.
On new iOS 10 the user can select inline playback with a pinch gesture over the full screen:
- On iPhone,
<video playsinline>elements will now be allowed to play inline, and will not automatically enter fullscreen mode when playback begins.
playsinlineattributes will continue to require fullscreen mode for playback on iPhone.
When exiting fullscreen with a pinch gesture,
playsinlinewill continue to play inline.