Capture Card Resolution -- was: Re: [mythtv-users] 2 Capturecard questions

Ken VanDine ken at
Sun Mar 23 23:23:46 UTC 2003

OK, much better now.  I increased the value of VMALLOC_RESERVE from 128 to 256.
 Now I can add gbuffers=64 without a problem.  Now, the quality is pretty good
at 480x480 and can't do any higher.  I do notice a little frame loss and will
try your test later on.  It is almost as good as my digital cable box now. 
Almost ready to use it full time.  :-)

Thanks for all the help.

Quoting Edward Wildgoose <edward.wildgoose at>:

> > Thanks, adding gbuffers=16 helps considerably.  But, gbuffers=32 just
> hangs
> > mythfrontend.  It still appears as if it is dropping frames in both
> rtjpeg
> and
> > mpeg4, but it is much better than before.  If the height for capture is
> set to
> > 240 it doesn't appear to drop any frames.  CPU load is fine, always at
> least 25%
> > idle.  I am using DMA for hd access and get ~30MB/s.  I did find some
> references
> > to gbuffers=32 on the web and people seem to have success.  Not me.  Any
> other
> > ideas?  Would it help to go to the v4l2 stuff and the lastest bttv
> driver?
> I am
> > willing to try anything.  One thing I have observed is the CPU usage of
> X.
> If I
> > capture at 720x240 X uses about 6-8% cpu.  Capturing at 352x480 X uses
> about 22%
> > cpu.  I don't think this is the issue, but might be something wrong.  I
> am
> > pretty sure the dropped frames are on the capture side, I always of idle
> %
> of 10+.
> I can use gbuffers=64 without a problem, so it sounds like a memory buffer
> problem somewhere.  I am using a vanilla 2.4.20 kernel (under gentoo), and
> settings in the BIOS seem quite normal, but fairly optimised.  AGP Window
> is
> 64MB I think.
> What I would suggest is that you try recording without using myth, try
> using
> lavrec (part of mjpegtools) and play with settings to see what works.  For
> instructions on using lavrec see the sourceforge site under the documents
> section - there is a howto there with a command line which works (you need
> the --software-encoding switch basically).  Lavrec shows clearly when
> frames
> are being dropped.
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Ken VanDine
biZrace Inc.
kvandine at

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