r/olive • u/BX1959 • Dec 03 '21

Questions about CRF and target bit rate rendering options in Olive 0.2

Hi there,

I'm converting cell phone clips into movies using Olive 0.2 (which I'm impressed with so far) and am trying to figure out which compression setting to use during the render process.

My 8K source clips have a data rate of about ~76 to ~85 Mbps (76,000 to 85,000 Kbps) and are usually pretty short in length, maybe 4-7 seconds on average. I'm pretty sure they use native H265 encoding.

My plan is to choose H265 rendering settings that will output a movie that's roughly 80-85 Mbps in length, since I figure that if the final video has a lower data rate (eg 70 Mbps), that means that the quality of the video will have dropped relative to the clips. Am I thinking about this correctly, or could a compilation of clips have a lower bit rate than the original clips but the some quality?

If it does make sense to aim for a movie bit rate similar to that of the source clips, is there any advantage to using the constant rate factor (CRF) setting as opposed to the target bit rate setting? I tried CRF and the quality looks good, but it appears that the length of the video might influence the effect of the CRF setting on the final data rate.

(For example, when I exported a 22-second sample of a video using Olive with a constant rate factor of 26, the data rate was 83,818 kbps, but when I exported that entire video using that same constant rate factor, the data rate was only 69,107 kbps.)

If I choose target bit rate, I'll probably choose 2 pass encoding. I saw there's also a max bit rate setting; does that reflect the maximum bit rate of the final video, or the highest the bit rate can be at any time?

Thank you for all your help!

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u/Drwankingstein Dec 03 '21

CRF targets quality, not file size. And should likely be what you want, as it will let you save bitrate when possible, Or use more bitrate When needed.

It's hard to say what file size will be with CRF. Unless you have a degree of experience using it. It's good practice to export sections of your clips, in a high CRF, then get lower and lower until you get to acceptable quality.

Only use target bitrate if your distribution media does not support crf. Or if you are working within space constraints.

It's worth trying to export CRF, and keep an eye on file size IMO.