I guess you were using the third party Dlls to get frame from the video files, and displayed the returned bitmaps in the PictureBox contro. Actually, I didn’t reproduce your problems which you said controls locked. However, with your code, only one picture can be seen even you use a “for statement”.
Please try the following changed code. Assume you have set the Maximum property of the TrackBar control to 100.
for (var1 = 0; var1 < this.trackBar1.Maximum; var1+=10)