Hi! I see you're having trouble with videos freezing or not downloading in the Substack app. I'd love to help get this sorted out. Just to clarify, are you experiencing this on the Substack app on your Macintosh running OS X 10.15.7, or are you accessing Substack through a browser on your Mac? And does the freezing or download failure happen with all videos or only certain ones?

In the meantime, here’s a straightforward set of steps to try that usually helps with video playback issues on Substack:

1. Check Your Internet Connection:
Make sure your Wi-Fi is stable. Try switching between Wi-Fi and wired connection if possible, or reboot your router.

2. Restart the App/Browser:
Close the Substack app completely or quit your browser and reopen it. This clears any temporary glitches.

3. Clear Cache and Data:
While the Substack app itself on Mac might not have an explicit cache clearing function, try clearing your browser cache if you’re using the web. For Safari on macOS 10.15.7:
- Go to Safari > Preferences > Privacy > Manage Website Data > Remove All.

4. Update Software:
Ensure your macOS and web browser (Safari, Chrome, etc.) are up to date. Outdated software can cause playback issues.

5. Disable VPN or Proxy:
If you are using a VPN or proxy, temporarily disable it as it can interfere with video downloads.

6. Try Another Browser:
If using a web browser, try an alternative like Chrome or Firefox to see if the problem persists.

If you’ve tried these steps already, please let me know, and I can guide you through more advanced troubleshooting or check if there might be any reported issues with the Substack video servers right now.

Does that sound good? Also, do you notice any patterns, like the videos freezing after playing a certain amount or failing right away? That can help narrow things down.