What renderer does the sequencer use to preview?

Hey,

I can’t seem to get anywhere near realtime playback in the sequencer. I’ve created a default blender scene with a camera spinning around the cube. If I view in rendered view through the camera it plays back in realtime completely fine but when I try the same thing in another scene in the sequencer it plays at around 3ish frames a second. I’m curious which renderer the sequencer is using and can I switch it to get better playback?

Thanks,
Mitchell