To: AugustBlade
Dear user,
The HD video that is imported to AVS Video Editor is being cached (you will see a mark on it in the media library), this is done to make the editing more comfortable and does not influece the output video quality.
What you experience is first minutes of the video has been cached already, while the rest - not, please wait for the caching process to stop. After that the video will play smoothly on the preview.
Please let me know if I can be of any further assistance to you.
Kind regards