I watched this and had no issues (using MPC-HC). I would try another viewer.
If you have problems watching, then the first thing to do is remux (I'll describe using ffmpeg as that is simple and what I always use). I have found that when there are playing issues that fixes 90% of them. When a simple remux doesn't solve the problem you can add the -copyts option - shown in brackets below because it can cause problems sometimes and is rarely necessary. ffmpeg is easy to find and download but is a command-line program.
How to use ffmpeg to remux:
ffmpeg -i input.mp4 -c copy [-copyts] output.mkv
If ffmpeg is in your PATH then "ffmpeg" is enough; if not, point to the program (c:\<full_path>\ffmpeg.exe).
The -i option is the name of your input file (note you can specify MP4 or MKV files).
The -c option tells ffmpeg which codec to use for encoding; for remux you don't want to encode, only copy.
The -copyts option says to use the TimeStamps in the original file but as that is often the problem you don't want that most of the time. Always try without it first.
The name of your output file goes at the end and the extension tells ffmpeg which container to use.
MP4 and MKV and AVI are simply containers for video and audio streams. MKV can have any kind of stream but MP4 and AVI have some limitations (audio I think but you'll have to do a little research if that is relevant). MKV puts the metadata for the streams at the beginning of the file while by default MP4 puts it at the end; the result is that with MKV you can begin to watch while the file is still downloading. I'm not sure exactly why remuxing from MKV to MKV fixes many playing problems but I assume it has to do with incorrect metadata that gets fixed as part of the remuxing process. Re-encoding a video file can take hours or tens of hours but remuxing should only take a minute or two.
