When comparing Mirillis Action! vs OBS, the Slant community recommends OBS for most people. In the question“What are the best screen recorders for Windows?” OBS is ranked 1st while Mirillis Action! is ranked 4th. The most important reason people chose OBS is:
You can record videos in formats such as mp4, flv, mkv, and more. You also have control over the bitrate used.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro It records without using the CPU and consumes less resources than OBS and is several times more fluid and intuitive
It consumes less resources and is more fluid than OBS. For example, a 1 GB GTX 750 records perfectly in 1920 x 1084 at 60 fps up to 4K, without using the processor, only the graphics card. Trying to do the same with OBS, the recordings do not exceed 15 FPS, nor is it possible to stream with OBS. With Mirilis Action it is possible to stream in high quality at 60 FPS, no matter the platform, it is fluid (tested with 8000Kbps upload and stream with 8GB Ram at 1600Mhz).
Pro The only software to record audio from selected application or game (not including unwanted sounds from the system)
Pro Recording webcam or USB/HDMI Capture Devices
Pro Records to many popular formats
You can record videos in formats such as mp4, flv, mkv, and more. You also have control over the bitrate used.
Pro Free and open source
No subscriptions or payments or licenses.
Pro Available for Linux, Mac, Windows
Pro Live streams
Can be used to stream.
Pro Fast
From the website: "GPU-based game capture for high performance game streaming."
Pro Extendable
OBS has an API allowing developers to create their own unique plugins, giving them and others complete control of their streaming experience.
Pro Encoding using H264 (x264) and AAC and file output to MP4 or FLV
Pro Unlimited number of scenes and sources
Cons
Con Recording a window will not record the menu bar, popup menus or child dialogs
Con Overkill for simple projects
Plus the interface is a bit intimidating.
Con Needs tutorial to get started
Otherwise it's hard to find out how to record a screen or window.