icloud video not playing the audio

Salutations pg1one, 

Are you able to record a new video on the same device and see if there is audio upon playback? How about if you then attempt to play it on another device? Let’s be sure to test using the camera that originally recorded the videos in question as each uses a specific microphone. If the microphones on your iPhone aren't working

Thanks. 

Hello pg1one,

It is odd that it would only affect those couple of days.

If you share the videos with another device, do they play with audio on the other devices?

From Share photos and videos on iPhone - Apple Support:

• Share a single photo or video: Open the photo or video, tap , then choose a share option.

Have a good day.

We understand pg1one,

If the videos previously had audio, do you sync with iCloud? If so, do they play from the site?

If not, do you have a backup of the videos? If so, you could restore from that backup, but would lose all of the data accumulated since then: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

We hope this helps.

Cheers!