[mythtv-users] Playback of HDTV, HDHomeRun

David Smiley dsmiley at mac.com
Sat Jul 19 06:03:57 UTC 2008


dsmolka at gmail wrote:
> On Wed, Jul 16, 2008 at 11:36 PM, David Smiley <dsmiley[at]mac.com>  
> wrote:
> >
> > I have a P4 at 2.8 GHz and I've been using it just fine with a  
> Hauppage 250
> > card for nearly a year.
>
> I'm in pretty much the same boat -- P4 2.5 with a Hauppage 250 and  
> HDHR.
>
> > I just purchased a flat screen TV and an HDHomerun.
> > I got the HDHomerun to record a snipped of a high-def program for  
> just 11
> > minutes (which was 1.26 GB !).
>
> This sounds about right. Maybe a bit on the high side but not far. I
> typically see around 6.5 to 9 GB per hour.

I knew it would be much more but it blew me away just the same as I'm  
used to 1GB/hour.

> > The playback is basically impossible; choppy
> > doesn't begin to describe it. I suspect it's some sort of super  
> high-res
> > MPEG2 format but I don't know how to get at info on my video files  
> so I am
> > not certain.
>
> I've got a similar problem (though not as bad as yours) that I've been
> trying to solve for some time now. Some channels (OTA) work very well,
> some are worse. Some channels are flawless, all are watchable, but
> some have minor problems with pixelization or stuttering.
>
> There are a number of factors that could be involved. With these CPU
> specs, I would expect you need hardware acceleration via XvMC.
>
> What's your video card? Are you using XvMC?

I forgot to mention such key info.  I've been using an NVidia GeForce  
FX 5200 because I heard Mythtv does a good job with them.  I pretty  
sure I'm using XvMC; though I'm not certain.

> Beyond that, it could be:
>
> A dirty signal -- have you tested your signal through, e.g. the HDHR's
> MS Windows utilities?
>
> Dirty cables -- are you sure you have good cables and aren't picking
> up any interference? What's the distance of coax between your
> antenna/source and HDHR? And powerful EM sources in between? Are you
> using a splitter to feed both inputs? Do you get a better result only
> feeding one input without a splitter?

This can't be it.  I took the transcoded file (the 1.1GB mpeg 4) and  
moved it onto my Mac (an underpowered 1.8GHz G5) and it played.

> Network congestion -- is your HDHR on a network node with any other
> devices? Is is going through a switch? How much other traffic is going
> on at the same time?

This is a single-box FE/BE; no network in the way for my problem at  
hand.

> I/O congestion -- What type/speed of HDD are you using? Are you trying
> to play back while recording? Do you have your MySQL database on the
> same drive as your recordings? Are there any other disk operations
> (e.g. transcoding, com flagging, mythfilldatabase, etc) happening at
> the same time?

My machine isn't doing anything else at the time.  I've attempted this  
several times of day for the same file with same results and I checked  
my CPU usage too; it was doing nothing before.

> > An auto-transcode of this file brought it down to only 1.1 GB
> > but that didn't help the playback (unsurprisingly).
>
> This would seem to suggest a capture issue rather than a playback
> issue. But are you sure the artifacts or other distortions are exactly
> the same on the original file and the transcoded file?

Ehh... well since mythtv deleted my original file after transcoding, I  
can't make a comparison.  But I'm not sure why you're asking this.   
Since transcoding is lossy, I'd expect it to be a little less quality.

> Your system should be HD capable with some adjustment, but it almost
> certainly requires XvMC and a bit of tweaking to the Playback
> Settings.
>
> With a bit more info we can probably help sort you out.

Thanks a LOT for your response; it's nice to see quality help like this.

By the way, ffmpeg -i tells me the following about the video stream:
Stream #0.0: Video: mpeg4, yuv420p, 1920x1088 [PAR 16:9 DAR 160:51],  
29.97 tb(r)

Hey, I just thought of something.  Since my flat-screen has a native  
resolution of 1360x768 (it's a 720p set), perhaps as part of my  
transcoding process I should ensure that anything that exceeds that  
resolution gets reduced to fit it.  That might explain my results thus  
far if mythtv had to scale it down on the fly.  My Mac, on the other  
hand, wasn't doing any scaling.  Can you tell me how to go about doing  
this?  Obviously I wouldn't want all my recordings going to this  
resolution since many will be 480i or whatever it is.  And another  
thing, I've got horizontal and vertical scaling 1% (only applicable to  
analog recordings but it's mythtv-wide) so I should try disabling that.

I need to do some more tests.

~ David


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