Short version

Record the whole run at 30 fps with a hardware encoder. Speed up the early rounds normally in your editor. For the late rounds, where the game stalls, remove the repeated frames first, then speed up; otherwise the timelapse gets choppier exactly where it should be most exciting. Add music last.

Plan the recording

  1. Record everything, locally. A freeplay run to round 300+ is hours long. Record to disk at 1080p30 with a hardware encoder (NVENC, AMD, Apple VT) so OBS doesn't take CPU from the game. Settings are in OBS settings for BTD6.
  2. Use MKV or Hybrid MP4. If the game or OBS crashes at round 400, a plain MP4 is unreadable. MKV survives; remux it afterwards.
  3. Keep the pause menu closed. Every menu visit is a cut you'll make later. If you need breaks, let the round end and pause in a predictable spot so they're easy to find.
  4. Play fast-forward from the start. The game's 3× speed is free time compression with no editing. Keep it on unless you're about to do something fiddly.

The late-round problem

From roughly round 150 on, the game can't simulate fast enough and the frame rate falls (why). Your recording keeps its 30 fps, but it does that by repeating frames while the game stalls. A 10-minute stretch of round 250 might contain only a minute of distinct frames.

If you apply 2000% speed to that stretch in an editor, the editor samples every 20th frame. Most of those samples land on repeats, so you get a jerky slideshow, and you've thrown away real frames to get it. The fix is to make the editor only see real frames.

Speeding up the early rounds (editor only)

Rounds 1–120 or so are smooth, so a plain speed change works:

  • Premiere Pro: right-click → Speed/Duration. Set Time Interpolation to Frame Sampling, not Frame Blending or Optical Flow (they smear the UI). Max is 10,000%.
  • DaVinci Resolve: right-click → Change Clip Speed, or Retime Controls. Set Retime Process to Nearest in the Inspector.
  • CapCut: Speed → Normal, up to 100×. Turn off smooth/optical flow.

Pick the speed by target length: a 2-hour recording to a 2-minute segment is 60×.

Handling the laggy rounds

  1. Trim the stretch you want. LagCut processes 30-second windows, so pick the moments that matter: a boss, a round-number milestone, the run ending. For a timelapse you want several short windows, not the whole hour.
  2. Run each window through LagCut. It removes the repeated frames and any pause menus, and exports the remaining frames at a steady 3× pace. Nothing uploads; it runs in Chrome or Edge.
  3. Drop the exports on your timeline in place of the original stretches. They're already compressed in time and already smooth, so apply a smaller extra speed-up, or none.
  4. Match the pacing. If the early rounds are at 60× and a cleaned late-round clip feels slower, speed it up a little; because it has no repeats, it stays smooth.

On real creator footage this turned 30 seconds of round 268 into 8.8 seconds and 30 seconds of round 400+ into 1.6 seconds of continuous play; the before/after clips are on the tool page.

Finishing

  • Round counter overlay. A simple text layer with the round number at each cut helps viewers follow a timelapse.
  • Audio last. Timelapses lose all original audio anyway; add music over the finished cut.
  • Export at 60 fps if your source and the cleaned clips are 30. YouTube handles it, and sped-up footage reads smoother at the higher rate.