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How does constant bitrate factor affect video quality when upgrading from 1080p to a higher resolution?

Constant Rate Factor (CRF) is a settings in video encoding that controls the quality and file size of the resulting video.

CRF uses a "constant quality" encoding mode that sets the quantization parameter (QP) to a specific value, balancing file size and quality.

Lower CRF values result in better quality but larger file sizes, while higher values yield lower quality and smaller file sizes.

CRF of 17 is often considered a good balance between quality and file size, however, using a CRF below 17/18 may not provide significant visual benefits and is mainly useful for those who don't care about detail loss.

CRF 12 and lower is often considered "transparent" for lossless or very detailed footage.

Not all video clips are equally easy to compress.

Low motion and smooth gradients are easy to compress, whereas high motion and complex scenes are more demanding on an encoder.

The average bitrate in MBit/s for 2160p encode at different CRF values can range between 10 and 25 MBit/s for a one-minute video clip.

For a 1080p video around 450MB, upgrading it to 4K can result in a file size up to 45GB, using the same CRF setting.

X264 codec with Constant Rate Factor (CRF) set to around 19 for very good quality, is recommended.

Handbrake, VidCoder, Ripbot264, TEncoder, FFmpeg are some of the tools that can be used for video encoding with CRF setting.

YouTube recommends 1080p Constant Rate Factor CRF value between 18 and 23 for acceptable results on their platform.

When encoding to CRF, it adjusts the data rate to achieve target quality as opposed to adjusting quality to achieve a target data rate.

In H264, QP ranges from 0 to 51, you can easily set a fixed QP for your entire encoding process with x264 and x265, but note that libvpx does not have a fixed QP mode.

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