Audio not playing in QuickTime Player video?

to record the mac's internal sound with quicktime you need additional software. i use a kext file from the retired soundflower app. the app no longer works but if you download the free kext file from this page it will do what you want to do. you will also need to set up a multi-output device in your audio MIDI setup utility. there are instructions on how to set it all up on the link i provided. one thing you should know is that the kext file is signed, but the installer is not, so you'll need to follow the instructions to the letter to install it. and just fyi, i downloaded and installed it while still on catalina, but the extension still works on big sur.

this is the file you need from the above page:

and since you have an M1 mac, you also need to look at this entire thread to get it up and running. there's instructions for M1 macs there.

tecsi12 Said:

"Audio not playing in QuickTime Player video? I was viewing and recording a video playing on my iPhone to my MacBook using QuickTime. At first I couldn't hear the audio, but I got that to work—can't remember how. I think I was using my headphones to listen to the audio. Now, replaying the QT video, the video is fine, but there is no audio. I was assuming I could be able to hear the same audio I heard while viewing/recording."

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Try Safe Mode:

[Hold Down command key + R key] simultaneously upon boot. In Safe Mode, corrupted system setting files (caches), are intentionally fixed.

1. Boot: in Safe Mode
2. Log In: as Same User
3. Try: Playing the File
4. Wait: 30 seconds
5. Shut Down: the Mac
6. Wait: 30 seconds
7. Boot: the Mac normally
8. Log In: as Same User
9. See if audio now plays.

Then...

Reset the SMC and NVRAM:

Sometimes changes are made to the system (i.e. updates) and then system settings (i.e. for Ports) become manipulated, technically. So try resetting the SMC and NVRAM on your Mac.