cMP unable to play h.264 4k footage properly in QT

[kgapp]

I have a fully loaded cMP (6 core 3.33, 48GB ram, RX580, PCIe SSD, etc.) that I am having difficulty smoothly playing h.264 4K 150Mpbs videos in Quicktime. The footage was shot with a Panasonic HC-X1. The video files do open in QuickTime but playback stutters quite a bit and many frames are lost.

These same h.264 files play perfectly in VLC 3.0 and other macOS video apps but QuickTime just can't play them back smoothly. I have to transcode them with Final Cut to AIC or ProRes in order to get smooth playback in QuickTime.

The h.264 files also play fine in QuickTime on my 2016 13.3" mBP so I am inclined to think it is the older Xeon processor in my cMP that is struggling. However, monitoring CPU and GPU activity during playback shows me that a very small amount of resources (under 15%) are being used by the system during playback.

Given that I am barely utilizing my CPU and GPU resources I can't understand why QuickTime is struggling so much when other apps (like VLC) can play the files back perfectly. I do realize that the older Xeon processors lack some of the modern functions for decoding h.264 video but this issue is exclusively with QuickTime and is not a system wide issue.

Attached is a screenshot of my system specs along with details on the 4k video file being generated by my Panasonic HC-X1.

Anyone run into this before? Any suggestions other than to not use QuickTime to play them back?

 

[smirk]

Is one of the cores saturated when trying to play back video in QuickTime? Maybe QT only decodes on one core (I don't know this, just trying to brainstorm).

 

[kgapp]

Is one of the cores saturated when trying to play back video in QuickTime? Maybe QT only decodes on one core (I don't know this, just trying to brainstorm).

I appreciate the response. The load seems to be spread out evenly on all cores. Verified with iStat Menus.

 

[smirk]

And you're playing them off of your SSD, right? So we can rule out slow disk access?

 

[bsbeamer]

8-bit or 10-bit? 4:2:0 or 4:2:2?

 

[kgapp]

And you're playing them off of your SSD, right? So we can rule out slow disk access?

Yes. I am loading the files from the SSD.

8-bit or 10-bit? 4:2:0 or 4:2:2?

Very good question. If memory serves the HC-X1 can not record 10-bit so I am pretty sure the video is 8-bit color. Not sure on 4:2:0 vs 4:2:2. Is there any application that can inspect the file and tell me which one of these it is?

As I mentioned above it is not really that the cMP can't handle it because VLC plays them fine. Its really just QuickTime and some inefficiency that appears to exist when trying to decode these files.

 

[kohlson]

I am assuming that this is on a "modern" QT app, not the old QT7. Just checking.

From the inspector window, what's the bitrate for the media?

 

[bsbeamer]

QT has a ton of playback issues with higher quality files with many codecs. It's been that way for a long time regardless of what Apple support will say or document. The new version of QT is actually worse than the old QT7 (with .component "plugins" added) for some codecs, but can barely play 4K files unfortunately. VLC knocks them all out without a problem.

If you're in VLC 3.0.4 Vetinari (Aug 9, 2018 update) there is a "media information" under window > media information. The general tab that pops up will be mostly blank. Click on codec details and you'll get a good report on color and the decoder being used. The statistics tab also helps during playback to see data rates.