Black Box HDMI to Video Signal Scaler and Converter

Yes it can scale 1080p HDMI in to 720p/60 out, video goes out both the Composite and Component video ports at the same time, in fact if you just press the 720p/60 button on the bottom of the remote then everything will be done. Audio is also extracted and will go out both the S/PDIF audio port and L & R RCA audio jacks, it samples audio at 48 KHz.

You would need to use this device to change your analog 8mm signal to HDMI and then connect that to a capture device (i.e. this Blutec USB model - https://bhpho.to/38fhT8F), which would then allow you to have your computer perceive the incoming signal in the same way it would see a webcam.