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X-T3 hevc video codec rate distortion / quality issues


micky.finn

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Obviously I don't have documentation for Fuji internal configuration of its video encoders for X-T3, but looking at a reference h.265 implementation manual, it seems rate distortion is a parameter used to increase compression at the cost of video frame rate distortion - namely jumpy video.

https://x265.readthedocs.io/en/default/cli.html#mode-decision-analysis

I find that 60fps 4K DCI 10bit 4:2:0 hevc long gop max bitrate is unusable because it is way too jumpy; 50 fps 4K DCI 10bit 4:2:0 hevc long gop max bitrate almost tolerable but does not look professional when object moving side to side with even moderate speed look like you selected the wrong shutter agle (I didn't) or it is dropping frames (I don't think it is). Even at 23.976 or 24 or 25 I still notice it sometimes - which doesn't make sense since the available bit rate is so much higher at the lower frame rates.

I tried asking Fuji and they said they looked at the video (and they were engineers not tier one help desk) and said they would have another group get back to me but have had no response for several months.

My guess is that the rate distortion quality setting is too aggressive. I have not tried external recording 10 bit 4:2:2 - maybe someone can confirm that the behavior disappears if the camera is not actually recording just passing through? I am especially interested in 4K DCI 10 bit 4:2:2 external 50 frames per second (I plan to post to 25fps - but as mentioned I notice this in all frame rates).

It is frustrating that they got so close to perfect value priced high quality cinema camera except for this behavior.

I am attaching a link to a small clip where you can see the traffic is jumpy left to right but not into camera - presumably these exercise different limits of the encoder - one causing rate distortion to fit within the bit rate available.

On the other hand it could also be that the Fuji engineers just left the parameter at a default setting (28?) that does a very bad job and could have set it lower and still fit within the bit rate available. But I am just guessing since I don't have access to any of the Fuji codec docs or parameters used :(

Does the Medium Format camera have same issues for 4K DCI video? At all frame rates?

Attached via link are two very short examples - but it doesn't matter if camera is on tripod, handheld, etc - always this jumpy motion for lateral movement.

https://www.dropbox.com/sh/4zaekotof54zxna/AABnVnXGpHbpimwvhWwJO2zQa?dl=0

 

Thanks

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