The issue with playing back footage that has been sped up significantly is with storage access speed, it needs to read the file that many times faster. You may notice a significant boost in performance by using an SSD.
Nothing you do, however, will make it perfectly smooth from my experience. My theory is that if you are using media with IPB or IPP compression (not all frames are the same, I think there's a techquickie on it), it still has to read multiple frames to get the data for each of the frames that appear in the timelapse, so performance is likely to stay laggy. The reason I have this theory is that I haven't seen as much of a slowdown speeding up media transcoded to prores or DNX, or all-I H264 media.
Regardless, from my experience realtime playback of any timelapse is futile, and it needs to be pre-rendered.
The way to make it playback nicely is to render out the clip. There are several ways to do this:
- You can cache your whole timeline, it's an option in the playback settings, it will act like final cut and prerender for playback (I keep render cache on smart)
- You can render just the timelapse clip by right clicking, clicking render optimized media
- You can export just the time-lapse clip and replace it (export, individual clips, select the timelapse).
Any of these 3 will give you perfectly smooth playback of the timelapse.