If you are a video editor or aspiring to be one, you must have come across the term ‘CRF’ while exporting your videos. It’s an important parameter that affects the quality and size of your output video. In this article, we will discuss what CRF is, how it works, and its impact on video quality.
What is CRF?
CRF stands for ‘Constant Rate Factor.’ It’s a video encoding parameter that controls the trade-off between video quality and file size.
CRF is used in most modern video codecs such as H.264, H.265/HEVC, and VP9. The CRF value ranges from 0 to 51, where 0 produces the highest quality but the largest file size, and 51 produces the lowest quality but the smallest file size.
How does CRF work?
CRF works by adjusting the bitrate of each frame based on its complexity. A complex frame with many details requires a higher bitrate to preserve its quality, while a simple frame with fewer details can use a lower bitrate without affecting its quality significantly.
When you set a CRF value, you are telling the encoder to maintain a constant level of visual quality throughout the entire video by adjusting each frame’s bitrate accordingly. The encoder will increase or decrease the bitrate of each frame until it meets the desired CRF value.
What is the impact of CRF on video quality?
The impact of CRF on video quality depends on two factors: source material and output resolution. If your source material has high motion or fine details such as text or patterns, using a lower CRF value will result in better visual quality as it preserves more details in each frame.
On the other hand, if your source material has low motion or less detail such as smooth gradients or solid colors, using a higher CRF value will result in smaller file size without noticeable loss in visual quality.
Similarly, the output resolution also affects the impact of CRF on video quality. If you are exporting to a higher resolution such as 4K or 8K, using a lower CRF value is recommended to preserve more details and avoid pixelation. But if you are exporting to a lower resolution such as 720p or 1080p, using a higher CRF value is acceptable as the details will be less visible at that resolution.
Conclusion
CRF is an important parameter in video encoding that affects the quality and size of your output video. By adjusting the bitrate of each frame based on its complexity, it maintains a constant level of visual quality throughout the entire video. The impact of CRF on video quality depends on source material and output resolution, and choosing the right CRF value requires balancing between visual quality and file size.
