This has just started happening for me now as well after updating to release 4.6.0. Only fails on MP4 recording. AVI is fine.
Have completely uninstalled Action and reinstalled no success. GFX drivers are up to date.
Windows 10 pro
RTX 2070 Super
60 FPS VFR
Active Screen = Desktop 1 (tried with 1 and 2, doesnt work)
Copying info from another post:
Does Action! crash only in MP4 format but not in AVI?
Yes, AVI records and exports fine
Do you use any external USB audio devices?
Normally I record to a USB3.0 Ex HDD. But on this occasion I am trying to record directly to internal SSD drive. I have an external USB 3.0 hub plugged in, with microphone, elgato capture card plugged into it.
dx diag report