No sound when video recorded in silent mode

I recently accidentally recoreded a video when I had my phone on silent, when I went to play the video, now with the sound on my phone on, there was no sound in the video. I thought this was because I recorded with my phone on silent but then spoke to a friend about it and he said that it still should have recorded sound and I should be able to hear it as long as my phone's not on silent when I play it. But this isn't the case. I also tried playing the video on my laptop and still had no sound, so for some reason it hasn't recorded any sound. Why has this happened and is there anyway I can fix it and somehow access the sound that should be on that video?