davidgphoto84 wrote:I copied it from the NAS to my PC.
If rendered local file is stuttering while playing back on PC but not stuttering when played back elsewhere even though it is on NAS then it is something about your PC. Have you tried observing your Resource Monitor to see what might be maxed out during playback? Hint: When observing CPU don't observe single average value, PC that has one core maxed out but has 20 cores will make you think CPU decoding is not the problem because it reports back average of 5%.
Also, fact that you don't have problem playing back same file when encoded as QuickTime hints you might be having a problem with codec you are using. What does MediaInfo say which codec you are using in the files that have problem with ones that don't?
Which software you are using when playing back stuttering files?