[mythtv-users] High timestretch speeds with VDPAU

Brad DerManouelian myth at dermanouelian.com
Fri Dec 12 17:36:33 UTC 2008

On Dec 12, 2008, at 9:23 AM, David Engel wrote:

> I like to watch most news and talking heads shows and occasionally
> some sports at fairly high timestretch speeds.  I'd like to hear if
> anyone has been able to achieve at or near 2x timestretch speeds using
> VDPAU on H.264/HD-PVR recordings?  I'd particularly like to hear what
> speeds others can get on 9300/9400 IGP systems since that's what I've
> been eyeing for a frontend upgrade.
> My testing Using a GeForce 9500 GT on my desktop system has been
> somwhat disappointing so far with respect to high timestretch speeds.
> I can get to about 1.55x for 1080i and about 1.75x for 720p before I
> start seeing prebuffering pauses.  By disabling deinterlacing, I can
> get an extra 0.1x or so to about 1.65x on 1080i.  The recording bit
> rate doesn't seem to make much, if any, difference.  For example, I
> get pretty much the same results with 1080i recorded at 6 Mbps as I do
> with 1080 recorded at 13.5 Mbps.  FWIW, this setup has no problems
> running 1080i MPEG2 and lower resolution H.264 at full 2x speeds.

On 13.5 Mbps 720p content, I can time stretch to 1.25, but 1.3+ has  
audio dropouts that make it too annoying to use. I haven't seen much  
mention of time stretching with VDPAU so I don't know if it's been  
optimized at all. There's likely some work still left to be done with  

720p HD OTA content works just fine up to the max of 2x using VDPAU.

I haven't been having much luck with deinterlacers lately so I turned  
them off and am letting my display take care of it so I can't tell you  
how timestretch works with them.


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