[mythtv-users] vdpau worth it for hdtv?

Brad Templeton brad+myth at templetons.com
Sat Nov 28 06:15:02 UTC 2009

On Mon, Nov 23, 2009 at 02:32:01PM +1300, Nick Rout wrote:
> 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:
> >> > 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.

     Stream #0.0: Video: mpeg4, yuv420p, 1920x1088, PAR 136:135 DAR 16:9, 30 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s

Disturbingly, I now see it is not the bandwidth to the video card
over PCI that is causing the problem.  I get the same problem
on my core2 duo system with a gt220 card on pci-e x16.

So I checked and myth itself is unable to play this video properly
any more (be it with vdpau or in cpu++ mode and the software decoder.)

xine and mplayer barf on the .nuv (not unusual) but VLC is able to play
the video smooth and fine, no vdpau.

So something else has gotten broken in the playback of the old transcoded
nuvs.  They play very jerky and with a strange distortion that's hard to
describe, it looks like a mixture of extreme deinterlacing artifacts
combined with mp4 artifacts, but it is not visible when playing with vlc.

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