How do I reduce lag when speed ramping 120fps videos in Premiere Pro?

Question

Hi,

I'm having trouble understanding why my plackback lags whenever I speed ramp my 120fps footage past 250%.

I'm shooting 120fps using my Sony a6400.
I've uploaded a clip to the sequence by choosing "New sequence from clip", which defaults to 119.88fps; 1920X1080.
On the clip itself, I choose "time remapping; speed" and make two points and increase that area to 250+%, which when I play it back, it lags pretty bad. Playing the clip with a speed ramp less than 250% works just fine!

I have CUDA enabled, have playback resolution set to 1/4, increased my RAM usage for PP to 29GB (MAX), cleared out cache, and I'm still getting lag!

Can anyone possibly give some tips or things I can do to not have this lag occur? I feel like I have a pretty dang good computer, so I'm not sure why this is happening when I've seen people on YouTube have their 120fps 1080 clips speed ramp to 1000% and have zero lag without them pre-rendering or creating proxies AND on a Mac!

Here's my computer specs:

CYBERPower PC

CPU: AMD Ryzen 7 3700X 8-Core Processor 3.60GHz
RAM: 32GB

GPU: GeForce RTX 2060 SUPER

STORAGE: 500GB SSD

Thank you for your help!

R Neil Haugen · Answer

I would expect lag and other playback issues if that is long-GOP media directly from the camera. An mp4/mov file basically. Sony's AVCHD is also typically long-GOP. That format records only a complete frame every 9-30 or more 'frames', and in between records data-sets of the pixels that 1) will change before the next complete "i-frame", 2) have changed since the last i-frame, or 3) both.

So the computer, for every frame, has to find the right two (at times 3!) iframes, decompress them, load the dataset, compute the pixels for that frame from comparing the iframes & dataset, rinse and repeat.

For every frame.

Now, when you speedramp, you make Premiere also throw some out or add some frames in depending on direction of your ramp.

That's a ton of processing. Your settings in Preferences for hardware encoding/decoding need to be set correctly for your machine. So go to the Edit/Preferences/Media tab, and try working with the H.264 encoding and decoding settings at the bottom of the tab. Depending on the CPU, you may need those set one way or another.

This video by Andy my help ... also, transcoding to an intraframe codec like Cineform, ProRes, or DNxHD/R can help in playback. Proxies can be problematic with time-remapped footage.

Neil

FAQ: My CPU is stuck at 100% ...

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