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Mr. M
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PostPosted: Wed Aug 01, 2012 1:29 pm    Post subject: random white pixels when playing video on thinkpad T61 Reply with quote

So, I converted my old thinkpad T61 (intel GM965 graphics) into a media computer with xbmc. First I had it connected to my TV using the VGA output. However, when playing video I noticed random white pixels in the video. The pixels are like "shot noise' they appear randomly flickering across the screen. It is not too bad, the video is watchable but it annoys me ;).

Anyways, I thought it may be the VGA connection, so I got an "Advanced Mini Dock" from eBay and a DVI to HDMI cable. The setup was easy, and xbmc now shows up in beautiful 1920 x 1080 resolution. I'm actually very impressed of how well the 5+ years old laptop handles HD video. Unfortunately, the white pixels still show up in the video. What's a bit suspicious is that they are only in the moving parts of the picture, e.g., they don't show up in the black bars at the top and bottom of the screen.

Has anyone here had similar problems? I tried upgrading x11-drivers/xf86-video-intel from 2.19.0 to 2.20.2 but there is no difference. In some other forum someone suggested that the GPU temperature may be too high. But I don't think this is the case, as the problem occurs right after booting and I recently installed a new fan, also lm_sensors doesn't show high temperatures.

Any hints what could be causing this are highly welcome.
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Hypnos
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PostPosted: Wed Aug 01, 2012 1:44 pm    Post subject: Reply with quote

Do you experience the same problem if you use a different media player, like mplayer or vlc?
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Mr. M
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PostPosted: Wed Aug 01, 2012 1:50 pm    Post subject: Reply with quote

Hypnos wrote:
Do you experience the same problem if you use a different media player, like mplayer or vlc?


No, actually I haven't. But I will try this tonight. Thanks for the tip.
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Mr. M
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PostPosted: Wed Aug 01, 2012 10:39 pm    Post subject: Reply with quote

Mr. M wrote:
Hypnos wrote:
Do you experience the same problem if you use a different media player, like mplayer or vlc?


No, actually I haven't. But I will try this tonight. Thanks for the tip.


I just tested it. The video plays fine in mplayer; there are no white pixels but the playback (1080P) is not as smooth as in xbmc. So the problem seems to be caused by xbmc or one of the libraries it uses (e.g. ffmpeg).

Any ideas what to try next?
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Hypnos
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PostPosted: Wed Aug 01, 2012 10:45 pm    Post subject: Reply with quote

It looks like xbmc depends on either ffmpeg or libav. You can try replacing ffmpeg with libav and see how it behaves.
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Mr. M
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PostPosted: Wed Aug 01, 2012 10:52 pm    Post subject: Reply with quote

Ok, it seems the video rendering method in xbmc is causing the problem. There are 4 options, "Auto", "Basic Shaders (ARB)", "Advanced Shaders (GLSL)" and "Software". By default the setting is on "Auto". I tied all the settings and the problem only occurs with "Advanced Shaders (GLSL)" and "Auto" (which chooses Advanced..). For now I put the setting to "Basic Shaders (ARB)". I will file a bug report with the xbmc.
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