I could be wrong, but I think the op is wondering if there's an app that'll record video in slow motion with "sound". Helpful instructions regardless, you just helped me
dschoenike
Glad that helped you. I think a lot of people never noticed that feature because of where it is located - not very intuitive. I was just clicking on every option when I got my phone so came across it. I usually have my sound muted on my own recorded videos so didn't realize it wasn't recording sound in slow motion though.
I did find an app that I just tested with a 30 second clip that plays back video recorded in regular speed in slow motion with audio. I don't know how this will work with a longer video or if the OP will find the quality acceptable but there's a free version with ads (paid with no ads) so they can try it out free if they want. It's call SlowPlay and is in the Play Store. It only has a 3 star rating so that's why I'm not sure how it will end up working out for a longer video or with other video formats. But it worked in my little test so someone who actually wants the slomo audio feature can test it out further since I only care about the slow motion video myself. I'll be uninstalling the app since I only downloaded to try to help out here.
I recorded a 30 sec video in the video camera at normal speed and while talking. I opened SlowPlay and imported the video from the Gallery. You can adjust the play speed up or down at set intervals. The audio is supposed to work from 50% speed to 200% speed. There is an option in the settings for this so make sure it is checked. For my clip the audio worked at 50, 75, 100, 125, and 150 percent speeds. It was all static at 200% but the OP wasn't asking about fast motion anyway. So try it at 75% or 50% and see if it's acceptable or not. Otherwise there are other apps in the Play Store you can try.