No sound from MP4 video in pdf

I am trying to put a video into an Interactive PDF using Acrobat DC Pro. The video is being found and inserted but, when played back, there is no sound. Other video's work in this document and this video works when played on the desktop. It just seems to have no audio when played in the pdf. Any suggestions? The original file was fomat VLC media file (.webm) and was converted to .mp4 using the VLC tool.