Pixelation-and accompanying audio stuttering

For some months, I have had seemingly random issues with pixelation-and accompanying audio stuttering. It does not matter what channel- and sometimes it stops after 5-10 minutes, and remaining recording is fine. And at other times, recording plays back perfectly.

I am viewing on Windows Media Center (.wtv). I selected WTV Unprocessed as my Profile for Removing Commercials. Would WTV or WTV Legacy be better?

I archive the original full-length recording- and when I try viewing that, it also has the identical pixelation/audio stuttering issue. So, something is going on with the original conversion- Handbrake and FFMPEG are way over my head!

My system: Windows 8.1Pro (updates shut off). CPU: Intel i5 with 10GB of RAM and NVIDIA GeForce GT 710 graphics card, version 398.82.

I have a log file from The Voice, where issue is especially bad. I think it is too long to place in this post. If needed, I can email, or post if necessary.

Thank you in advance for any guidance.

Chris