I'll see if I can reproduce this. 1) If the video is 100 BPM, and the audio is playing at 120 BPM, then the video will play at 1.2x speed. 2) If the Serato track slows down to 85 BPM, then this 100 BPM video will then play at 0.85x speed. 3) The "Beats" allows you to set the duration of the clip in beats. So, if the video is exactly 2 seconds long, and you set the Beats value to 4 (that is, telling MixEmergency that the video has 4 beats over 2 seconds), then MixEmergency treats this video as though it is 120 BPM.