"Normal" will play the video once for the duration specified. If the length of the video is less than the duration, the effect will appear blue until the end duration.
"Normal No Blue" will play the video once for the duration specified. If the length of the video is less than the duration, the effect will appear blank until the end duration.
"Loop" will loop to the beginning and play the video again if it ends before the duration of the effect.
"Slow/Accelerate" will adjust the video speed to fit the duration.
"Manual" allows you to manually set the video length with the duration text box.
"Manual and Loop" allows you to manually set the video length with the duration text box and then will loop the video.