FCP 10.5.2 4K HEVC artifacts at chapter markers

I have the same issue also with FCP 10.5.4. The export often might have a duplicate frame and several frames with blocky artifacts at chapter points when exported via Apple Devices 8-bit 4K HEVC with "Include chapter markers" ON. (I sent feedback also to Apple about this).

There are no such artifacts if I:

- Use 10-bit 4K instead 8-bit 4K with chapter markers.

- Use 8-bit HD instead 8-bit 4K with chapter markers.

- Use 8-bit 4K with "Include chapter markers" turned OFF.

FWIW I checked a few such chapter points with Avidemux and there seem to be several blocky P B frame pairs at those blocky chapter points.

Has no one else seen this behavior? I could reproduce it in a new project at almost all such chapter points. (Mac mini 2018 with clean Big Sur 11.4 install with no major extra add-ons). Maybe I should routinely use 10-bit HEVC because as an added bonus it has somewhat finer gradations in some scenes although it is at least 5x slower than 8-bit.

I wondered why I sometimes could not provoke those blocky artifacts that plague FCP 10.5.4 8-bit 4K HEVC export. I might have found the answer for that:

4K HEVC at 25 fps seems to have the following repeating frame pattern (checked with Avidemux):

IBPBPBPBPBPBPBPBPBPBPBPBPBPBPBP [31 frames]

IBPBPBPBPBPBPBPBPBPBPBPBPBPBP [29 frames]

IBPBPBPBPBPBPBPBPBPBPBPBPBPBPBP [31 frames]

IBPBPBPBPBPBPBPBPBPBPBPBPBPBP [29 frames]

etc

If the chapter marker happens to be on a P frame, this breaks the pattern at that point making the previous B frame a P frame so that there are two adjacent PP frames -- the latter P frame and the remaining PB pairs then all have those blocky artifacts until the next I frame clears the movie until it happens again.

So in worst case if the chapter marker is at the 3rd frame of the 31 frame block, there are 29 blocky frames before the next I frame clears the scene.

This issue does not seem to affect 10-bit 4K HEVC (at quick glance the frame pattern seems to be different with only I and B frames) or 8-bit HD HEVC.

The same chapter artifacts are seen also in Compressor 4.5.4 4K preset with HEVC Faster (standard quality) 8-Bit and 10-Bit Color export options (both are OK with the Slower (higher quality) option).

I have not yet tested how this relates to 30 fps 8-bit 4K HEVC.

To summarize my tests what setting to use in my workflows:

Final Cut Pro 10.5.4:

HD_HEVC_10-bit -> OK

4K_HEVC_10-bit -> OK

HD_HEVC_08-bit -> banding in some scenes

4K_HEVC_08-bit -> chapter artifacts, banding

4K_HEVC_08-bit_nochapters -> banding

Compressor 4.5.4:

10-bit_slower -> OK

08-bit_slower -> minor banding

10-bit_faster -> chapter artifacts

08-bit_faster -> chapter artifacts, banding

So for 4K HEVC with chapters and the best quality it is tempting to use the 10-bit HEVC FCP preset (8-bit would be 32x faster in my Mac mini 2018 because AFAIK it uses T2 for HW acceleration...) or Compressor's 4K preset with 10-bit Slower option (10-bit Faster would be 50x faster). I can use those faster options if I don't use chapters.

I try to report these issues to Apple.

- Matti

It seems the T2 chip in Mac mini 2018 does not do a good job at HW accelerated 4K 8-bit HEVC export with chapters. In Mac Book Pro 15,4” 2014 the same 8-bit HEVC export does not have these artifacts and the GOP pattern is different (but the CPU export is MUCH slower. I check the GOP pattern with Avidemux).

Below is a dropbox link (37 MB) to a sample Final Cut Pro project and an input file for Compressor that has the same artifacts in 8-bit HEVC export with these settings:

Final Cut Pro 10.5.4 > File > Share > Apple Devices 4K... > Settings > Format: Apple Devices, Video Codec: HEVC 8-bit, Resolution: 3840 x 2160, Include chapter markers ON.

Compressor 4.5.4 has the same artifacts in Mac mini 2018 (4K_HEVC_10-bit_chapters_mbp.m4v input with Compressor > Video Sharing Services > 4K > Video > Codec: HEVC, Encoder type: Faster (standard quality), Profile: 8-Bit Color).

The input has a chapter at frame 2 and the 8-bit HEVC output has many blocky frames until the next I frame.

Can you reproduce the artifacts in another T2 or Silicon Mac??

https://www.dropbox.com/s/38iyfub60lkinkc/4K_HEVC_08-bit_chapters.zip?dl=0

OK, the previous samples did not go through. But I did a better and a more more basic test after deleting all old FCP projects and resetting FCP prefs and creating a brand new 4K project with minimal edits to the imported DJI P3P 4K mp4 (just straight cuts and added chapter markers via keyboard shortcut m m -- and click the far right marker icon at the top to set a chapter marker. So excuse me the faded D-Log colors and the tilted horizon).

And once again, the 4K HEVC export with chapters ON has several frames with blocky artifacts (notice the white rock in the lake at the lower right and numerous other artifacts in the 1st image) while in the same frame (and all others frames) export with chapters OFF is OK (in this particular spot the frame at the chapter marker was not duplicated).

Yes, that is a frame at a chapter marker. There are several such frames at and just after the chapter marker, I just picked the one that most clearly shows the artifact blocks that are clearly seen to briefly pop up in the movie. Chapter markers are inside a continuous shot with no edits whatsoever. The original movie had some chapter markers at edit points but I could not readily detect any artifacts there.

I usually edit and export DJI P3P 4K footage to an HD project which has always been OK with chapter markers (just HD to save some space because IMHO the HD vs 4K output difference is negligible with 4K footage from such a small detector). This time I used key frames to fix the tilted horizon and decided to test whether I could see any artifacts caused by a small digital rotation & zoom in those 1-2° rotations even in 4K. But those chapter marker artifacts ruined it all.

Thanks for the thought! In the former edit at an 2x to 1x speed edit point there was a chapter frame that went backwards in time and it was the most disturbing glitch.

I wonder why my usual HD output seems to be immune to this error.

I hope FCP folks pay attention. Or maybe I should post also to Apple's feedback black hole.

https://www.apple.com/feedback/finalcutpro.html

Just for fun I had created a routine 8-

bit and also a 10-bit HEVC HD export that at first glance seemed to be identical with that DJI P3P input.

AFAIK the 10-bit does not use the macMini 2018 T2 chip for the encode so it was about 5x slower with CPU instead GPU.

I expected similar quality, but surprisingly with closer inspection the slower 10-bit export had more depth in this short scene (notice the gradations in the lake at the lower left -- exaggerated with this jpg export screenshot [edit: and also no so clearly seen in these attachments]. On the other hand, the HLG Dolby Vision export was too dull with this input).

> Could you ZIP the library and upload it? Dropbox has broken the bundle into a folder structure.

The dropbox link should have the zipped 4K_HEVC_08-bit_chapters.zip file with a folder that contains:

4K_HEVC_08-bit_chapters folder:

4K_HEVC_08-bit_chapters.fcpbundle -> sample FCP project [I can open it by Option-launching FCP]

4K_HEVC_08-bit_chapters.m4v -> Mac mini 2018 export with the artifacts

4K_HEVC_10-bit_chapters.m4v -> sample input file for Compressor [the same file is in the FCP project]