Problem with encoding video by chapter

[nghiabeo20]

I have a limited resource (4720HQ). Encoding a whole bluray in one try would fry my laptop. So, I decided to encode each chapter of the BD remux into one mkv, and use concat muxer of ffmpeg to join them together. However, the joined video has so many artifact that doesn't appear in the original inputs.

Here's a sample:

https://drive.google.com/open?id=1wn0cyQaVs5iUnC1Jx13kBizKoiqBp567

The two inputs mkv don't have any weird artifact at all, but the artifact is clearly visible in the output video (for example, around the 8:02 mark). How can I eliminate these artifact? Some posts insist that I have to reencode with the --stitchable option, but I cannot find such option in x265. Is it true?

Thanks for your help!

[tuanden0]

You can use mkvmerge to join (append) each chapter together without encode.
Without re-encoding => no artifacts.
Then, If you want to encode to h265, using the new output instead of encoding each chapter then join them

[nghiabeo20]

You can use mkvmerge to join (append) each chapter together without encode.
Without re-encoding => no artifacts.
Then, If you want to encode to h265, using the new output instead of encoding each chapter then join them

You can check my sample, sorry it's rather large. The weird artifact doesnt come from reencoding. I use both ffmpeg and mkvmerge (which uses ffmpeg anyway) and the artifact is still there. It wasnt reencoded because both program join tee file in less than 1 minute, and the quality of the scenes without artifact is still great. Even ultrafast cant be that fast.

[Selur]

I use both ffmpeg and mkvmerge (which uses ffmpeg anyway)
a. mkvmerge doesn't use ffmpeg
b. merged 1.mkv and 2.mkv using mkvmerge played the resulting file in MPC-HC using the gpu decoder from my NVIDIA card, checked the cut point -> no artefacts