[mythtv-users] vdpau worth it for hdtv?

Nick Rout nick.rout at gmail.com
Mon Nov 23 01:32:01 UTC 2009

On Mon, Nov 23, 2009 at 2:01 PM, Brad Templeton
<brad+myth at templetons.com> wrote:
> 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.

ffmpeg -i filename.avi

should tell you the codec.

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