There is not a purist’s argument to made here. This isn’t even like MP3s cutting off highs and lows in music that are audible on CDs.
It just wastes space by compressing less in areas you really won’t notice. But isn’t that other way, constant QP, really better quality in the end? If you’re using x264, CRF is used by default for constant quality. Subjectively, the video will seem to have higher quality. Because of this, a video compressor can apply more compression (drop more detail) when things are moving, and apply less compression (retain more detail) when things are still. The eye perceives more detail in still objects than when they’re in motion. It does this by taking motion into account. The quantization parameter defines how much information to “throw away” from a given block of pixels.Ĭonstant Rate Factor, on the other hand, will compress different frames by different amounts. In tech speak, that’s maintaining a constant QP (quantization parameter). The way constant quality encoding is usually done, it keeps up a constant quality by compressing every frame of the same type the same amount. A change of ☖ should result in about half/double the file size, although your results might vary. Is the file size too high? Choose a higher CRF. Is the quality good enough? No? Then set a lower CRF. If you’re unsure about what CRF to use, begin with 23 and change it according to your subjective impression of the output. The default for x264 is 23, so you can use this as a starting point.įfmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4 You can set the values between 0 and 51, where lower values would result in better quality (at the expense of higher file sizes). The Constant Rate Factor (CRF) is the default quality setting for the x264 encoder.
Quick Summary: What is the Constant Rate Factor? Filed under: Definitions | Tags: CRF |ĬRF stands for Constant Rate Factor, x264’s best single-pass encoding method.
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