[mythtv-users] HDTV/CPU survey

Daniel Thor Kristjansson danielk at cat.nyu.edu
Wed Apr 28 13:30:06 EDT 2004

Hey John,

I managed to borrow a GeForce 4 MX card and it doesn't give me any
playback problems using XvMC except with frame skipping and OSD. i.e.
when there is on OSD playback is fine even on 1080i material. My
processor is only a 1.7Ghz P4 with 333Mhz DDR-RAM. So I think that
brings the variables down to compile options, myth settings, or sound

This is with my playback patch, which does require at least i686
and -O3 compilation to work quickly. (cmov instruction, and branch
removal really.) With 1080i my patch only displays one field so
not having deinterlacing isn't a killer. Umm, I've also had problems
with extra audio buffering with XvMC, though I need it with software
decoding, go figure.

I'm working on the hdtvrecorder at the moment, I really want to be able
to get the SAP audio (I'm learning Spanish) and subtitles when
available. Though text looks pretty complicated with ATSC, two
different huffman tables just for English, with different tables for
different countries, and some UTF-16 text sprinkled here and there.
PMT's that don't agree with PSIP, ugh.

-- Daniel

On Tue, 27 Apr 2004, John Patrick Poet wrote:

]I have seen a few people with Pentium4 processor report that they are
]happy with the playback of HDTV material.
]I, however, have not seen a single "success" report from an Athlon user.
]Is anyone getting acceptable HDTV playback under Myth, with an Athlon
]processor?  If so, what speed, etc?
]I am personally using a 2.6 GHz Pentium4, overclocked to 2.8GHz.
]HyperThreading is enabled, and I have dual channel 433 MHz memory.
]With this system, HDTV playback is pretty good.  Not perfect, but very
]watchable.  The only time I noticed that my machine cannot keep up, is
]on *some* camera pans.  In those situation, I do get some *minor*
]pause/skip/pause/skip type studdering.
]I have XvMC disabled.  Enabling it results in very jurky playback of any
]OSD, and does not seem to improve the playback of the video.
]For those stations broadcasting in 1080i, enabling a deinterlacer is a
]must.  A deinterlacer, of course, make no difference for the 720p
]Experimental A/V sync does not seem to make any difference for me.  I am
]using nVidia's 5336 driver, so maybe Experimental A/V sync does not
]Extra audio buffering is required to keep the sound from studdering.
]If I enable "use video as timebase", I do not get any audio, and the
]video looks like it is running at about 90% of full speed.  This would
]indicate to me that my machine cannot keep up with HD streams, and yet
]gkrellm never shows my CPU above 65%.  My system "load" and disk
]activity also remain low.  This all make me very curious as to why the
]HD stream cannot be played at full speed without any frame skipping.
]I am planning on eventually building a dedicated Myth frontend.  The
]reason for this survey is to help me decide what hardware to go with.  I
]am somewhat tempted to give an Athlon a try if someone can indicate how
]well they work with HD material.  Anyone tried an Athlon64?

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