I have a couple hi-def movies, 1280x720, each is about 700mb, and all videos are of the same size, video codec and audio codec. All the movies can be played without any problem. I used mencoder from the mplayer package to merge them into one file. The command I used was:
mencoder *.wmv -oac copy -ovc copy -o video.wmv
But when I play video.wmv, the picture becomes lagged, it seems each frame will stay for 2-3sec. I tried to play with totem & vlc, both give the same results.