Granny Smith

Q: hdmi poor video quality (choppy)

I currently have a Dell 30" monitor hooked up to my MacPro 3.7 GHz Quad (Late 2013) via thunderbolt.

In an effort to utilize my MacPro as a media machine I ran an HDMI from it to a LCD TV (1080p). The video output is choppy and not smooth. I would think that my MacPro could easily drive a consumer television. Is there something I'm missing?

Mac Pro, OS X Yosemite (10.10.4)

Posted on Aug 1, 2015 11:39 AM

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Q: hdmi poor video quality (choppy)

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  • by lllaass,

    lllaass lllaass Aug 1, 2015 12:39 PM in response to Granny Smith
    Level 10 (188,781 points)
    Desktops
    Aug 1, 2015 12:39 PM in response to Granny Smith

    What TB port is the monitor connected to?

    Are you using a TB port that is different than the one used for HDMI?

    The bottom two TB ports and the HDMI port use the TB bus 0

    Mac Pro (Late 2013): Using multiple displays - Apple Support

    Does the TV an another input like DVI or displayport/mini displayport?

    HDMI is not the best.

    What specific model TV?

  • by John Lockwood,

    John Lockwood John Lockwood Aug 3, 2015 5:05 AM in response to Granny Smith
    Level 6 (9,309 points)
    Servers Enterprise
    Aug 3, 2015 5:05 AM in response to Granny Smith

    What are you trying to display on the TV that is choppy? I presume it is not something as basic as word processing or running a web-browser.

     

    If it is playing a DVD or a video file then I am afraid things are a lot more complex than you might think. There are various different 'speeds' of video, the following are the main ones.

     

    NTSC TV 60 interlaced frames per second - 60i

    PAL TV 50 interlaced frames per second - 50i

    PAL DVD 50 interlaced frames per second - 50i

    NTSC Film 24 progressive frames per second - 24p

    NTSC Blu-Ray 60 progressive frames per second - 60p

    PAL Blu-Ray 50 progressive frames per second - 50p

     

    Note: The first two speeds apply to standard resolution and high definition TV broadcasts, and many but not all NTSC DVDs. (Some NTSC DVDs are recorded at 24p). Also while for simplicity I like many others have listed this as 24p it is actually in nearly all cases 23.976 which is (24 x 1000) x 1001 = 23.976. (Don't bother asking why )

     

    For completeness real 'film' in cinemas was exactly 24 progressive frames per second not 23.976. These days however most cinemas actually use digital video files not old style film. When 'film' is being converted to a video file at 23.976 it is actually slowed down very slightly from 24 to 23.976, this means it would take a tiny amount longer to playback the full video than the original cinema film. In this case the difference is so small you cannot tell. However if one is converting between NTSC and PAL then the duration of a full length movie can be noticeably different.

     

    Now the reason why these speeds are important is that if your TV or more accurately your computer is configured to output to your TV at say 60 frames per second but you are actually playing a video recorded at a different speed this can result in juddering as every so often it will have to either throw away a frame or duplicate a frame to 'catch up' the difference. Most modern TVs can do 50i, 60i, 50p, 60p and higher end ones also 24p, however sometimes these different options are not advertised to the Mac properly or the Mac or a particular model of Mac may in particular not spot 24p. Even if the Mac spots 24p and offers it there is a widespread belief that Apple incorrectly do it as really 24fps and not the proper 23.976fps. This mis-match will again result in some juddering.

     

    TVs and computer monitors are supposed to use a standard called EDID to advertise what resolutions and speeds the TV/monitor supports to the playback device in this case your Mac computer. Sadly I find many fail to do this 100% properly. See https://en.wikipedia.org/wiki/Extended_Display_Identification_Data

     

    It is some times possible to use a software utility called SwitchResX to either tweak the settings or add missing settings to help out. See http://www.madrau.com/

     

    Again an issue to be aware of is that while some DVD or Blu-Ray players will automatically adjust the output they send to the TV to match the video rate, the Mac typically does not so you might need to manually check the rate the video file is recorded in and manually set the Mac to output at that rate.

     

    While most Mac video playing software does not auto adjust the speed/frame rate of the Mac video card to match the file being played so as to avoid judder, XBMC now called Kodi-TV is supposed to be able to do this. This is sadly an area that Windows software handles better.