[mythtv] HDTV patches

Daniel Thor Kristjansson danielk at cat.nyu.edu
Wed Apr 14 23:33:14 EDT 2004

The frame skip ratio is the ratio of frames that would not be skipped if
frame skipping were happending. It's debugging output that should have
been disabled. The value usually ranges between 0.33 and 0.5. This
detection is done at a low level so it's not surprising that commercial
scanning triggers it.

As for the performance problem. There are several possible causes.
First, if the frame size is small, software decoding my simply be
faster on your machine than the current XvMC implementation, especially
with OSD. Second there seems to be some unfortunate interaction between
audio and video decoding. I've found that with software decoding using
the extra audio buffer is better than without it, but with hardware
decoding it's the opposite.

I'm working on idct acceleration right now, which may make hardware
decoding with an idct capable card much better. This would include some
GeForce 4 cards, all GeForce FX cards and the ATI 9800 and later.

Finally there is a possible hardware problem. Sometimes the fan fails or
a power connector is lose on a GeForce card. This seems to cause it to
enter a low performance mode with little warning.

-- Daniel

On Wed, 14 Apr 2004, John Patrick Poet wrote:

]Hey Daniel,
]I noticed that the frontend spits out message along the lines of "frame skip
]ratio", or some such.  I assumed that this message was part of your code,
]and indicated a need to skip frames to "keep up".
]However, I also see these message from mythcommflag.  Why would the
]commercial skipping detector need to skip frames to "keep up"?
]I use your patches, but do not currently have XvMC enabled.  Even with your
]patches, enabling XvMC causes my output to studder more than with out it.
]Do I not have something configured right?
]Thanks for all the work you have put into this.

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