You used to be able to record audio directly into a container field, but this feature was removed after version 12.
If you're on a Mac, I'd look into using AppleScript to open QuickTime Player and start recording, then another AppleScript to stop recording, save the file to a temporary location, and insert it into the container field.
I was sure that used to be a feature... wonder why they did away with it? I'm on Windows.
It has been my experience that FileMaker was never able to import large FM files with audio data without crashing. I always assumed that was the reason why this feature was silently removed in FileMaker 13. A workaround is to simply import and export the audio files one at a time which never caused a single crash in over 5 years in my solution but requires a lot of scripting.
Additionally the audio recording was always limited to one minute in duration but at least it allowed for the use of audio plug-ins which were able to record longer time frames. However, they all became worthless with the release of FileMaker 13. All audio plug-ins also require QuickTime which is no longer supported on Windows.
Interestingly enough audio recording is possible with the iOS version. It was added to iOS version right around the same time the old record functionality was stripped from the desktop version. I am still hoping for its glorious return.
I'd hoped that maybe there was a plugin that provided this functionality. In my case, I only need short notes... my solution is for my own automotive repair shop: I want to be able to take some quick notes if someone calls and my hands are too greasy to type. I suppose the steno pad and greasy pen will have to do.