The output video from the SeeMusic app has a slight lag when the notes do not fall; please help me with this.
My PC specs: Pentium Gold G5400, 16 GB RAM, GeForce GTX 650 Ti
Software: Windows 11, SeeMusic 6.0.3
Recording device: iPhone 11 camera and iVcam v7.3.2.1850 for the source video (1920 x 1080 at 60 fps), then mix the source video, MIDI, and audio in SeeMusic for the lagging output as attached video.
The issue is almost definitely the combination of your new iPhone video format on your Windows PC - this isn't SeeMusic's fault per se - it's Windows Media Foundation not being able to properly handle the Apple format.
On your iPhone:
Open Settings
Camera
Formats
Choose "Most Compatible"
You will need to rerecord your video, sorry.
The other option would be to transcode your existing videos using an app like Handbrake.