We have checked with macOS Serria and macOS High Serria but it works fine in our tests. Can you please share the log of ActivePresenter so we can analyze further. To view the log, click ACTIVEPRESENTER > Preferences…> Miscellaneous > View Log.
2017-12-13 19:16:12: ActivePresenter 6.1.4 (Release Build: 2017.11.24) started
OS: Mac OS X (Darwin 16.7.0 x86_64). Version: 10.12 - 64 bit
CPU Count: 8
Computer Name: Mac-mini.local. Memory: 16,376 MB. Available: 2,825 MB
Project Location: /Users/Soul/Documents/ActivePresenter/
Disk Space: 189,495 MB (Free: 44,160 MB)
2017-12-13 19:16:12: TempDir: /Users/Soul/Library/Application Support/ActivePresenter/temp
2017-12-13 19:16:52: flt sample format is not supported, s16 will be used
2017-12-13 19:16:52: Preparing to record audio from: Built-in Microph. Channel: 2. Sample rate: 44100. Sample Format: 8
2017-12-13 19:16:59: Start capturing. Mode: Full motion. Method: 0. Capture Size: (2560, 1080)
2017-12-13 19:16:59: Video Codec: flashsv. Expecting FPS: 30.00
2017-12-13 19:16:59: Video will be recorded to: /Users/Soul/Documents/ActivePresenter/Untitled_tempdir/video_20171213_19-16-59.mkv
2017-12-13 19:16:59: flt sample format is not supported, s16 will be used
2017-12-13 19:16:59: Audio will be recorded to: /Users/Soul/Documents/ActivePresenter/Untitled_tempdir/audio_20171213_19-16-59.wav
2017-12-13 19:16:59: Preparing to record audio from: Built-in Microph. Channel: 2. Sample rate: 44100. Sample Format: 8
Unfortunately, we still couldn’t find any clue from the log. Can you please let us known is there any other message shown up when the program crashes? Please also try to record with a smaller dimension (such as 1280x720) to see if it works or not?