[pvrusb2] high latency

[Mike Isely]

On Fri, 29 Dec 2006, Michael Krufky wrote:

> Mathieu Bouchard wrote:
> > Hi,
> > 
> > I tried to plug a video game console into the wintv pvr usb 2 to play some 
> > games with my laptop screen while my girlfriend is watching the tv. 
> > Unfortunately, there is a latency of about 2-3 sec. between input and image, 
> > so the games are unplayable.
> > 
> > Is this a limitation in the hardware or a software problem? I didn't tried the 
> > device on windows yet and I'm using the module provided with the 2.6.19 
> > kernel. I tried with xawtv and mplayer. The image is 720x480 and my laptop is 
> > a pentium M 1.4 ghz with 512 mb of ram.
> 
> An mpeg encoder is not the best choice of a video capture device for use with
> an interactive system, such as a video game.
> 
> By design, as the hardware receives the video, it is encoded into mpeg, which is 
> sent to the pc over the usb bus, only to be decoded in software to produce the
> video that you see.  Naturally, there will be somewhat of a delay, and this cannot
> be avoided.
> 
> This delay can be reduced if you have a hardware mpeg decoder, however, the delay
> will still be present -- just a bit less.  Still, this is no solution for a video
> game console.
> 
> If you want to use your computer as a display device for a video game console, I
> recommend that you use a raw analog "dumb" framegrabber, instead of an mpeg encoder.
> 
> Hope this helps,
> 
> Michael Krufky
> 

Mike is correct.  This device really isn't the best choice for such 
applications.  It's just goes with the territory.  The pvrusb2 driver 
does do some buffering internally, but I believe the majority of the lag 
you see is buffering internal to the device plus the latency of the mpeg 
encoder itself.  The hardware is really optimized for reliable error 
free video streaming, not isochronous transit like what you would need 
for gaming.  Sorry :-(

  -Mike

-- 
                        |         Mike Isely          |     PGP fingerprint
     Spammers Die!!     |                             | 03 54 43 4D 75 E5 CC 92
                        |   isely @ pobox (dot) com   | 71 16 01 E2 B5 F5 C1 E8
                        |                             |