Unlike the Average Bitrate which aims at outputting the target file size according to the video bitrate you set, Constant Quality is unusable for adaptive bitrate streaming, that is to say, there are no bitrate controls (variable bitrate with no upper data limit), there could be huge data rate swings within the file that potentially disrupt the switching algorithm used by your selected ABR (Average Bitrate) technology. Subjectively speaking, 18-28 is a reasonable range, and 18 is often considered to be approximately lossless from a visual point of view. If the output file is too large, please set a higher RF value. If the output quality is not satisfactory, please set a lower RF value ģ.

If the output quality is satisfactory and the file size is as expected, 23 (or 28 for x265) is an appropriate RF value Ģ. A change of ☖ should result in about half/double the file size.ġ. The default for x264 is 23, and x265 is 28, so if you are not sure about what Constant Quality value you should use, you can begin with the default value 23 or 28 and adjust it to lower or higher according to the output quality you want to achieve. Under the x264 and x265 encoding, you can set the values (Rate Factors) between 0 and 51, with the lower values delivering the higher quality, and high values resulting in more compression and lower quality. If you are not sure what is Constant Quality mode and how to use Constant Quality while converting or rendering a video, you can read this article for a basic reference.Ĭonstant Quality is a kind of x264 and x265 encoding mode to adjust the rate up and down to achieve the visual quality level rather than the specific data rate. To get the best balance between the video quality and file size (get the higher video quality but in the smaller file size), the main video converters or video editors adopted the Constant Quality as the x264 and x265 encoding mode. While ensuring the highest compression rate in a single encoding, each frame is allocated enough bits to achieve the required visual quality. Constant Quality mode aims at achieving a fixed visual quality.

There are two types of high-quality video rate control models for H264/ H265 encoding: Constant Quality and Average Bitrate (2-Pass ABR) mode. What Is Constant Quality and How to Use It?

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