[Webkit-unassigned] [Bug 181445] WebGL video texture black in Safari 11.0.2 and wrong colored in Safari Preview 11.1

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Jan 10 09:34:39 PST 2018


https://bugs.webkit.org/show_bug.cgi?id=181445

--- Comment #15 from Jer Noble <jer.noble at apple.com> ---
(In reply to Klaus Reinfeld from comment #5)
> (In reply to Jer Noble from comment #2)
> > It looks like this video is encoded in '420f' pixel format, meaning YCbCr,
> > full-range. We may have a bug in our YUV->RGB conversion for full-range
> > video. As a workaround, you may want to try re-encoding your source video in
> > video-range '420v' pixel format and see if that corrects the incorrect color
> > issue.
> 
> Yes, the video is (and should be) in full-range format.
> It was encoded using ffmpeg.
> 
> I have made now here a new example that allows switching between videos with
> several pixel formats (all encoded using ffmpeg):

Thanks for making these test cases, this will help with debugging quite a bit!  It'd also be helpful to post the command line you passed to ffmpeg to generate these samples so we can reproduce the outputs with other test media.

Since WebKit on Mac and iOS use AVFoundation to do video decoding, one way to test for basic decoding support would be to load these .mp4s in QuickTime Player (which also uses AVFoundation). Here's what I see on my High Sierra machine:

> https:///krpano.com/video/pixelformattest/
> 
> (click the gear-wheel icon in the right-bottom and then pixelformat to
> change the video)
> 
> Here the results:
> 
> 4:2:0 16-235 (yuv420p) 
> - shows only the first frame in Safari 11.0.2

Loads in QTP, and colors look correct.

> - works in Safari Preview 11.1 but the colors are slightly different to
> Chrome (not sure which ones are correct)

Are you explicitly specifying color primaries and a transfer function? WebKit and Blink may be choosing different defaults in the absence of explicit color metadata.

> 4:2:2 16-235 (yuv422p) - doesn't load at all

Fails to load in QTP

> 4:4:4 16-235 (yuv444p) - doesn't load at all

Fails to load in QTP

> 4:2:0 0-255 (yuvj420p)
> - shows only the first frame in Safari 11.0.2
> - wrong (green-tinted) colors in Safari Preview 11.1

Loads in QTP, colors look the same as yuv420p.

> 4:2:2 0-255 (yuvj422p) - doesn't load at all

Fails to load in QTP.

> 4:4:4 0-255 (yuvj444p) - doesn't load at all

Fails to load in QTP.

I suspect that the 422 and 444 formats aren't supported by AVFoundation's AVC decoder. This piece of the issue needs to have a Radar filed against it; it's a platform bug and not a WebKit one.

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