I'm not an expert in this field. Perhaps others will jump in to correct me or offer other advice. But I don't think additional software would help. The reasons why online videos start and stop are usually related to (1) your internet download speed; (2) your available RAM; (3) other programs that might be running in the background; (4) possible malware on the computer; and (5) the software you're using to view the videos may have become damaged or corrupt. And there may be other reasons as well.
Problem 1: Just as an example, let's suppose your internet download speed is 3 Megabits per second. Let's further suppose the video you're trying to watch needs a download speed of 4Mbps or higher to play smoothly without those annoying stops and starts. No amount of additional software will solve that issue in my opinion. (Using additional software might actually contribute to
Problem 3, above.)
Problem 2: Some videos get stored in RAM when they're first streamed to your computer. The video will then be played from the RAM. As the video is played, more video is downloaded to fill up the newly created empty RAM. (Think of a pail with a hole in the bottom. You fill the pail up with water. The water drains out of the hole creating empty space at the top of the pail. You continue to add more water.) If you add too much water at one time, the pail will overflow. If too much video is being "poured" (streamed) into your RAM you're going to have playback issues and it might help to max out your available RAM.
Problem 3: If your computer is running other programs in the background such as anti-virus scans, automatic updates, anything at all that uses up computer resources, videos can suffer.
Problem 4: Malware. Should be self explanatory. If you haven't run a full scan recently, you might want to --- just to rule out that possibility.
Problem 5: Have you tried using a different video player to see if that makes a difference? A lot of people recommend the
free VLC.
A final thought about streaming videos (viewing in real time online) vs. viewing offline after downloading to your computer. Let's suppose it takes you 10 minutes to download a 5 minute video to your computer. Is the download time greater than the time it would take to watch the video streaming in real time, even with all the stops and starts?