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+--- Thread: CRF settings question. (/t-crf-settings-question)
CRF settings question. - SjoerdHekking - 2023-09-08
Dear reader,
I am currently using 18 for both H.264/5, the movies look great and are almost indistinguishable from their original uploaded media.
However, after doing a lot of research, I found out that setting it to 0 causes extreme file sizes, in the area of 50GB for a transcoded-(ing) file. I was wondering, is that 5%~ of better quality (according to someone who made a nice comparison list) worth it?
Can I "sanely" set the CRF to maybe 12~'ish? What should I expect on the file sizes and the quality?
Lastly, I am using a P4000, so I am not "that" worried about performance, currently it's transcoding large 8gb mkv files with 300-400fps, so I don't mind have it work more.
RE: CRF settings question. - TheDreadPirate - 2023-09-08
The range of quality possible is ultimately determined by how good the encoder is. In my experience with Pascal's NVENC, anything below a 16 resulted in huge increases in bit rate with no perceivable increase in quality.
RE: CRF settings question. - Efficient_Good_5784 - 2023-09-08
I've noticed that with VAAPI HWA, the CRF settings don't do anything.
I have tried setting the CRF settings to the lowest and highest quality and comparing the final transcode, but both transcodes with VAAPI just look the same.
It only ever worked with software transcoding for me.
Ideally, you want to watch your content as close to the original source's quality. When transcoding, you're just re-encoding the content. Each time a video file is re-encoded, more information is lost. But since transcoding doesn't replace the original file, this is fine.
Your goal would be to set CRF values that would produce a transcode around the same quality as the source. The values depend on a lot of factors, like the quality/efficiency of the encoder, the video file in question, and how powerful your hardware is.
There is no point in using up more hardware utilization and temp disk space to create a bloated transcode so that no quality is lost during the transcode. As in, after a point, really low CRF values keep using up a lot of space and power just to get ever-so-close to the original quality of the source video. You can't create a better looking video by increasing CRF values. Your limit is the original source.
Most people set their CRF values around 20-16.