"Stream Size" and stuttering?

I have a few video files which will not play when streamed. These files play fine, however, when run from the hard drive.

All of these files are hi-def, all of them are .mkv, and all of them show a "stream size" entry when I run them through MediaInfo.

Similar files which run fine (hi-def and .mkv) do not show a "stream size" when run through MediaInfo.

So...can anyone educate me as to why some files have a "stream size" and why it seems to be the only similarity between the files that I am having a hard time playing?

Thanks for any help any of you gurus can offer.