This can happen if the device is showing a complicated scene, and doesn’t have the ability to play a video smoothly at the same time. If you have a complex scene, try simplifying it, or consider linking to the video.
This can also happen if the video file you have uploaded is very high resolution. Try using a video convertor or requesting a lower resolution copy from the video supplier. Although most videos for screens are 1080p or 4k pixels, in AR you can use much lower resolution (as the video doesn’t fill the screen). We recommend 720p or lower, and find most videos still look fine in AR at 640x320.
The final reason is if the 'bitrate' of the video is too high. This means you are asking the user's device to download too much too quickly and it has to wait for the video download to 'catch up'. We recommend a bitrate of 2Mbps/2000Kbps , which works out around 15MB per minute.