Problem with video format

[MarkKane]

Hello there. So I have a problem: when I record in MP4, both the game and the output video lag considerably.
When not recording, I get 100 FPS on CSGO; recording on AVI 1080p gives me 60 FPS, which is fine; when recording in MP4 1080p however, it drops to an uncomfortable 30 FPS or lower. What can I do? Is there a way to reduce the lag (without having to change resolution maybe)?
If it can be useful, I have an Intel i5 and a 755M. Thanks.

[Piotr]

Check if hardware acceleration is available. If you record in MP4 without hardware acceleration then you won't get much out of it.
If hardware acceleration in not available then it is better to record in AVI.