What is bitrate and what is its purpose in screen recording?

Whether it’s recording new videos or editing existing ones, it is important to remember about setting up the software so the final video looks in desired way. While there are many simple options such as “frames per second” or “video resolution”, it might still be possible to record a video with horrible quality if bitrate, which works completely independently from the former two, is set to minimal value. So what exactly is bitrate in a first place? Bitrate is the amount of data needed to encode a video within given timeframe (usually within one second). Most of the time, those are measured in megabits (Mbps) or kilobits (kbps). It directly affects the quality of a video as well as its size.

Correlation between resolution, FPS, and bitrates

The codecs used in the process of video making play an important part when it comes to final video quality. It attempts to compress the video so that it fits in a specified amount of Mbps file. For example, if a 720p video recorded in 24FPS is compressed into 5Mbps file, the overall quality of it will be acceptable because the codec correctly compresses the file. If the same video was recorded in 4k quality (2160p) in 120FPS and was excessively compressed to fit into 5Mbps file, then certain (if not most) of the details would be distorted, pixelated or simply indescribable.

The compression result is also affected by the amount of details and scene that is being recorded. Most people were extremely satisfied when codec H.264 was released, because it allowed compression that managed to fit greater resolution and high FPS files into lower Mbps files in comparison to even older codec types. Currently there are even better codecs in use such as H.265 which further decreases the amount of bitrate to store data in a single file. More on that in my previous post.

CBR and VBR

Another feature that is included in many editing softwares as well as in screen recorders is ability to switch between CBR and VBR.

CBR stands for “constant bitrate” and just as the name stands for, it encodes the video at the same bitrate throughout the entire recording (or rendering process in case of editing). What it means in practice is that no matter what kind of scenes there are on the screen, the same amount of bitrate is being used in encoding process. In this case if the bitrate is incorrectly setup, the video might lose its quality during scenes where there are the most details (in case when the bitrate is too low) or have considerably higher file size (in case when the bitrate is unnecessarily too high). CBR is recommended mainly in streaming PC activity to online services such as YouTube and Twitch to avoid errors and disconnects. For more information read this note on Twitch.

Twitch recommended bitrate ranges between 2 to 6 mbps, depending on the quality, but those values might even be much higher when streaming in 4k.
YouTube streaming bitrate should be around 6 to even 80mbps when streaming in 4k. To make a proper 4k stream on YouTube, you need very strong PC and extremely fast Internet connection.

CBR can also be used during steady scenes such a vlogs where the picture remains mostly unchanged.

VBR (variable bitrate) as the name suggests, changes the bitrate depending on the requirement. It is definitely much better optimized in terms of quality as well as file size than in case of CBR. Simply speaking, VBR allows setting a range with minimal and maximum bitrate desired to capture high quality video in every section. For example, if minimal bitrate value is 1 Mbps and maximum is 20 Mbps, then scenes where the screen is black will use only 1 Mbps while the scenes with highest amount of details in 1 second interval will be encoded in 20 Mbps (if required). Thanks to that option, every scene is immaculate and the file size is considerably smaller than it would be in CBR 20 Mbps video file. Two main drawbacks of this method is that some older electronic devices might not support it as well as the rendering/encoding time is significantly extended due to the complexity of the process. For those who, have already recorded and edited their video, use only one PC to render the video in separate software, this might be especially problematic since the rendering process of edited video takes up to 100% of CPU usage, slowing the computer use. Keep in mind that VBR does not negatively impact CPU usage while recording with Mirillis Action!. This applies only to post-editing process in separate video editing software.

Bitrate in Mirillis Action!

Action! allows setting custom and constant bitrate for live streaming ranging from 0,6 Mbps to 20 Mbps depending on the desired stream quality. When it comes to normal video recording, Action! by default uses variable bitrate to adjust to the scenes in recorded screen. Thanks to that, file sizes are always minimal, saving space for more videos that you can produce on your PC.