Videos on mute

Hi there. When I save videos from my WhatsApp into my photos, for some reason it mutes the video. I didn't have this issue with my iphone 5. Not sure if this is a WhatsApp issue or an iphone issue. Thanks for your help.

I just did a test video on my iphone and when I go into my photos to watch it, there is no sound. I tested it on my partners phone too and same thing, so it's clearly a setting on my phone