Why does FTB start lagging as soon as I start recording?

I want to record a "Lets Play" for youtube of a FTB modpack but as soon as I start recording it drops from 70fps to less than 10. I can't record with this much lag. How can I optimize FRAPS to reduce the amount of lag it causes when I start recording?

minecraft-java-edition minecraft-feed-the-beast

Best Answer

This depends on 3 primary factors:

Your CPU (Primary cause of issues while recording)
Your RAM (Can cause issues if it's too small, otherwise won't cause any issues)
Your hard-drive (Can cause some issues, but won't be as significant

The main thing is that recording the screen takes a lot of CPU resources. Now my PC is at 1920x1080 resolution, and here are some of the results I get while recording using both software that I own:

Terraria:

Normal: 55-60 FPS
Fraps: 10-15 FPS
Bandicam: 10-25 FPS (I got some weird figures with Bandicam)

Skyrim:

Normal: 25-30 FPS
Fraps: 3-9 FPS
Bandicam: 7-12 FPS

The worse-off your CPU is, the more significant the difference is going to be. Remember that your recording software is going to pull a copy of the frame and encode it all through the CPU. That's a big overhead that leaves your game with a significantly smaller amount of CPU to actually run the game.
Unfortunately you need a beast of a CPU to be able to record the screen and play modern games at a decent framerate.

Another potential issue is the amount of RAM that you have, although this is now less of an issue than several years ago where some programs would cache huge amounts into RAM.
If your RAM usage nearly exceeds the amount of memory that you have, then your system is going to fall back on its page file system, which is essentially RAM on the hard-drive. Anything stored in memory this way means that access which would be in the range of microseconds is now in the range of milliseconds, again thrashing your game's performance to nearly nothing any time that it needs access to RAM that's on the hard-drive.

This type of issue can sometimes be resolved by getting more RAM.

Either way, the general problem here is that you have likely a PC which is very underperforming for this type of work. Unfortunately there's no really easy fix.

If you want to know how I've solved this, I ended up (actually very recently) purchasing an Elgato Game Capture HD, which encodes externally to the PC, which records from my PC, encodes, and records to files on a separate laptop. There are several solutions out there as well, alternatives would include things such as the Hauppauge HD PVR 2.