[mythtv-users] vdpau worth it for hdtv?

Brad Templeton brad+myth at templetons.com
Mon Nov 23 01:01:28 UTC 2009


On Mon, Nov 16, 2009 at 02:50:36PM +1300, Nick Rout wrote:
> On Mon, Nov 16, 2009 at 2:45 PM, Brad Templeton
> <brad+myth at templetons.com> wrote:
> > On Sun, Nov 15, 2009 at 10:09:32AM -0800, Kevin Johnson wrote:
> >> If it is true that vdpau is less tolerant to errors, then that is a huge deal for me.  All my tv is ota, and I get some errors due to my distance from the stations.
> >> Can anyone else confirm this?
> >>
> >>
> >>
> >>
> >
> > I would be interested in reports on this from others as well.  I found that with
> > vdpau the errors would cause a brief flash of the entire screen to noise while it was
> > better handled in the regular decoders.    However, I presume that this is not a hardware
> > thing, and that over time the nvidia driver or whatever is controlling the decoding
> > of the mp2 will get better at errors.
> >
> > I also have noticed that vdpau is not able to play old videos I transcoded on the
> > system with the 8400gs over PCI bus.   They are super jittery, playing just perhaps
> > 5 frames/second.    On my 220GT card on PCI-E, it plays them better, but still not
> > perfectly.   It may be necessary to code up a mode that reverts to non-vdpau
> > playback for certain codecs.    Or indeed, it might make sense to be able to define
> > a key which changes the playback method from one profile to another, so that if
> > you are playing a video that has lots of noise in the stream, or a codec that
> > vdpau is slow at, you can switch back to software encode.
> 
> what codec are you using on those "old videos". xvid and clones do not
> make use of vdpau on the 8400. Therefore you will be using software
> decoding. Two points arise: is your cpu up to it? And can the PCI bus
> cope with the data? (when vdpau is used the compressed undecoded video
> is sent over the bus - this datastream is within PCI bandwidth. When
> the cpu has decoded it must then send the uncompressed decoded video
> over the PCI bus to the card, I haven't done the maths but PCI /may/
> not be up to it?

The codec is whatever mythtv's transcode put into them.   So based on what you
say, it's not doing vdpau and is thus doing direct display -- which used to
work fine (there is enough CPU) on the AGP video card, but not on the PCI 8400gs
card.    So the bad news is that switching to PCI with vdpau means you *must* use
vdpau, as you can no longer feed HD to the card fast enough.


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