when internet is slow then the video that i made to look verticall is stretched. How to fix that issue?

i have some video that i wanna show on site , and thoise are verticall video and by default SS show video in 1080/1920 format type i think, so used this code 

.sqs-native-video .native-video-player {

padding-bottom: 100% !important;

}

to make the video vertcall, but issue is when internet is slow and page loads the videos play late, untill than there will be a stretched pic showing over it, that is it by default , i dont want that stretched image, how to fix that. i have attatched image, with two pics stretched