ffmpeg compress video in fast motion in high quality
I, finally, found the answer!

The problem was created from the mismatch of Video frames duration, and audio duration. So the video seems to be frozen after some moment, and it seems it continues to play frozen to last video frame. However, audio continued to play. It continue to paly until audio duration finish. Therefore, I decided to remove the audio track entirely while compressing the file. This resulted a video-only file with correct playing time using "-an" ffmpeg option.

ffmpeg -i video_out.avi  -r 16 -crf 18  -vcodec libx264 -vb 10M -vf "scale=1280:720,setpts=0.25*PTS"  -an  gp.avi