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I am running OS X 10.11.6 and I have a strange problem with video. When I watch youtube video in FireFox (50.1.0, updated often), I see video flickering (fast blink) whenever the progress bar is shown. That includes when I move my mouse or kept my mouse pointer on the progress bar.

It seems that whenever there is an image overlay, the video will flicker. This does not happen in Safari but happens when I watch Amazon video in Safari. This problem has been bothering me for months. I cannot figure out how to resolve it. Please help!

Edit: I'm using the native HTML5 codec. Flash is disabled.

Here is an example of video causing problem: https://www.youtube.com/watch?v=coDff5RLIas

However, I noticed that not all video flicker as bad. Here is an example that seems to only flicker in full screen: https://www.youtube.com/watch?v=coDff5RLIas

  • Are you playing it through Flash or HTML5 video or what? – Spiff Mar 12 '17 at 18:09
  • Questions: (1) Does it flicker with Hardware Acceleration on and off? (Firefox: Options / General / Advanced) (2) Does it flicker with full-screen on and off? (3) Does it flicker with HTML5 enabled or not via youtube.com/html5? – harrymc Mar 15 '17 at 8:32
  • @harrymc, you maybe on to something. If I enable hardware acceleration, I do not see this problem. Without HA, I see flicker regardless of fullscreen. On the other hand, I don't have a way to enable or disable HTML5 playback. The page does not give me an option to choice. The check boxes cannot be selected. – some user Mar 15 '17 at 18:37
  • Youtube may not be giving you the choice because Flash is now abandoned by just about everybody. If the video codec you are using is slow, or your CPU is slow, the playback may not keep up with the timing on the video frames, causing flicker. Using HA means that some work is offloaded from the CPU to the GPU which is better suited to the job. Shall I put this up as an answer? – harrymc Mar 15 '17 at 18:58
  • I am holding out for a better answer. I have a late model MacBook Pro. Even if no HA is used, it should be more than capable of decoding YouTube video. In addition, flickering (which the video is blinking quickly) is not the same as stuttering (which is a sign that CPU struggles to keep up). Also I am still having issue with Amazon video at full screen. – some user Mar 16 '17 at 18:23
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It seems like Hardware Acceleration solves the flicker problem. This option is turned on by default, so it is a bit puzzling why it was off for Firefox.

To explain what it does : GPU-accelerated computing offloads compute-intensive portions of the application to the GPU, while the remainder of the code still runs on the CPU. While the CPU is designed for general-purpose operations and consists only of a few cores optimized for sequential serial processing, a GPU has a massively parallel architecture consisting of hundreds if not thousands of smaller, specialized cores, designed explicitly for graphical operations.

That's why using GPU operations, the display of video frames is accelerated. As each video frame is timestamped, if its display is not fast enough and takes too long, the video playback may need to skip a few frames, which will cause a flicker.

to enable Hardware Acceleration in Firefox, use the menu Tools > Options > Advanced > General > Browsing, then check "Use hardware acceleration when available".

Whether Hardware Acceleration works or not is depended on the video card and its driver. Some unfortunate users are forced to turn it off.

  • Same in Fx 63.0.1 on Mojave - but only if default was checked off and hardware acceleration was also checked off. I wonder why it was turned off – mplungjan Nov 3 '18 at 8:55

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