Timeline export failures will happen on FCP 10.6.5 (and likely earlier versions), starting with Ventura 13.4 on Apple Silicon, if the timeline export contains any Sony 100 fps or 120 fps 10-bit 4:2:2 XAVC-S (H264) clips. It happens regardless of timeline frame rate or export codec. Whether the 100/120 fps material is retimed makes no difference.
Failure modes include: high CPU slow export, or apparent success but no output file appears on disk, or output file is unreadable, or output file is readable but shows damaged frames. It does not happen on Intel. Also, it does not occur on Apple Silicon with 100/120 fps 10-bit 4:2:2 XAVC-HS (HEVC) clips or with 100/120 fps 8-bit 4:2:2 XAVC-S clips.
I have not tested H264 10-bit 4:2:2 100/120 fps from other camera codecs such as Canon, Fuji or Panasonic.
The exact failure mode can vary, but the failure itself is 100% consistent. Even a single clip of the XAVC-S 100/120 fps material in a timeline of other codecs or in a pure ProRes 422 timeline will cause export failure.
Existing properly-functioning FCP projects created on prior versions of MacOS will begin having this problem if the Apple Silicon machine is upgraded to Ventura 13.4. The problem cause is evidently MacOS not FCP.
The clips show in the Event Browser and timeline as black, audio plays but no video. However, it is not merely a playback problem within FCP; the export will fail or produce a damaged file.
Resolve Studio 18.1.4 has a similar problem on the same XAVC-S material starting with Ventura 13.4. Like FCP, it works OK on Intel. Premiere Pro 23.4.0 works OK with this material on Ventura 13.4 Apple Silicon.
Apple Pro Video Formats were unchanged for Ventura 13.4, still on version 2.2.4. Unknown if that is related.
Ventura 13.4 machines tested: M1 Ultra Mac Studio, M2 Pro Mac Mini
Ventura 13.3.1(a) machines tested: M1 Max MacBook Pro 16, 2017 iMac 27
You can *avoid* it for new material by recording in 100/120 fps 10-bit 4:2:2 XAVC-HS (HEVC). For 100/120 fps 10-bit 4:2:2 XAVC-S (H264) material already recorded, the only solution is use an Intel Mac, revert the Apple Silicon Mac to 13.3.1(a), or transcode the existing XAVC-S clips to HEVC using Handbrake.
Note this is not an FCP bug -- it also happens on Resolve. It is an issue with MacOS 13.4 on Apple Silicon.
The core problem is a decoding failure isolated to MacOS 13.4 on Sony 100 fps and 120 fps 10-bit 4:2:2 XAVC-S material on Apple Silicon. Because the decode side fails, it cannot transcode those to ProRes or anything else.
The options are externally transcode those clips using Handbrake before import to FCP, or (for new material) set the camera to record in XAVC-HS (HEVC) instead of XAVC-S (H264), or downgrade to MacOS 13.3.1(a), or use an Intel Mac which does not have this problem. It is not just FCP, Resolve also has the problem on Ventura 13.4 on Apple Silicon. For some reason it does not affect Premiere.
In further testing, the problem is not isolated to Sony 100/120 fps XAVC-S 10-bit 4:2:2 material. It also happens with DJI 5120 x 2700 10-bit 4:2:0 H264, 23.98 fps or 29.97 fps. I'll do more testing tomorrow.
Ventura 13.4.1 was an urgent security-only fix. The problem with XAVC-S and DJI 5k 10-bit H264 are reportedly fixed in Ventura 13.5 beta 3, so the expectation is that will be in the final release. I don't know the ETA.
Resolve (which is also affected) allows disabling H264 and HEVC video acceleration. When you do that the problem does not happen. This implies the underlying issue is the Apple Silicon video accelerators or how Ventura 13.4 uses those.