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Extreme, erratic luminance glitches in H.264 output file
I’m exporting preview files for the director of a project I’m working on. Source media is QuickTime H.264 1920×1080 23.98fps shot on a Canon 5D Mark III. Sequence settings match the source media. Before export, the sequence is nested and cropped to 2.39:1 (producing a letterbox), and TC/Clip Name window burn are added via an Adjustment Layer.
Exporting from PPro timeline into AME Render Queue, settings H.264 (MP4) 1280×720 23.98 5 Mbps CBR.
Encoding in AME proceeds as expected. I spot-check the exported media files and everything looks great. I upload them for the director to review.
A couple hours later, I get a phone call from the director. He’s complaining that the brightness is “glitching” at certain spots. He gives me a list of timecodes where it’s happening, but I see no problems on my end. As a quick fix, I upload the files privately to YouTube so he can continue his review.
Surprisingly, the problems persist for him, even after YouTube has re-converted the file. Again, it looks fine on my end. This makes me suspect that it’s a problem with the machine he’s watching from.
So finally I get to take a look at the video on his computer, and here’s what’s happening:
Every few minutes, usually right after a cut, the image will get very bright for a few frames. Almost like a inverse solarization – blacks and shadows become almost pure white, midtones are affected less. Then the image will revert to normal for a few frames, and then will get darker and more contrasty for a few frames. It alternates between the normal and darker frames for a few seconds, then stops for another several minutes until the problem occurs again.
Has this ever happened to anyone else? Any ideas what’s going on?
For reference, the system that is exhibiting these problems is a 2010 MacBook Pro, 8 GB RAM, OSX 10.6.8. The video was created in PPro / AME CC on a Mid-2012 MBP Retina (10.8.4), 16 GB RAM, and plays fine on that system, as well as on a Mid-2010 12-Core MacPro (10.8.4). Our DP also reported seeing these problems, though not as frequently, watching on a 2009 Dell Inspiron desktop running Windows Vista.
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2 Replies
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First try to verify whether there are issues with the encoded files. Download the transcoded YouTube video and pull it into Premiere with the H.264 file you exported. How do the encoded files compare to your final sequence in the Premiere project? If there are problems with the encoded files, try exporting with CPU-only Mercury Playback Engine instead of GPU acceleration.
If there are no apparent problems with the exported files then there is probably a compatibility issue. Try changing the H.264 export settings to Baseline Profile @ Level 3.1/3.2, two-pass VBR, target 7-10 mbps, maximum 14-20 mbps, and a key frame distance of 12 frames. On the Multiplexer tab select MP4 with Stream Compatibility set to Standard.
Thirdly, export a test clip using different codecs such as DNxHD or QuickTime H.264.
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Thanks for the advice. I think using CBR might be the culprit, as I didn’t get any complaints on earlier versions, when I was using 2-pass VBR. Still doesn’t necessarily explain why it works on my systems but not others, unfortunately.
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