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Not sure if this is the correct community, but I have a question about video encoding and decoding.

I have a video that gets served in MP4 or WebM formats, depending on browser support. I noticed that in chrome, the WebM is noticeably darker than when viewing the files locally in VLC, or even another browser such as Firefox:

Chrome

Chrome WebM vs MP4

Firefox

Firefox WebM vs MP4

The original issue was with videos that I was re-encoding myself with ffmpeg:

ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 2M output.webm

I thought it might be related to the CLI options I was passing in, so I tried playing around with some other encoding option (such as using Constant Quality (CQ) mode and two-pass encoding) but still saw the brightness differences in Chrome. After that, I noticed these same issues on media that was automatically encoded from cloudinary, and I figured if I am seeing the differences there, it probably doesn't have anything to do with my encoding option flags.

Before I go too much down the rabbit hole here, is there anything I can control with this? Or is this just an issue with the decoder Chrome happens to be using (which is different that what VLC or Firefox is using).

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4
  • If you disable hardware video decode in Chrome, is the rendering still different?
    – Gyan
    Jan 16, 2019 at 10:03
  • Huh, that does fix it! Navigating to chrome://flags/#disable-accelerated-video-decode, the option was set to Enable (which I think means it was using hardware video decoding, the option name is a bit confusing...). Setting that to Disable and then relaunching Chrome, and the WebM video displays the same as the MP4. So it seems like a bug with GPU decoding?
    – romellem
    Jan 16, 2019 at 15:56
  • 2
    Yes, either the decoder isn't passing along the colorimetry info or the renderer in that pipeline isn't acting on it. See existing issue at bugs.chromium.org/p/chromium/issues/detail?id=851216
    – Gyan
    Jan 16, 2019 at 17:18
  • I tried lookup up a relevant chromium bug earlier but didn't come across that one. That looks to be exactly the issue I'm seeing! Thanks for all your help.
    – romellem
    Jan 16, 2019 at 19:15

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