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

Edward Wildgoose edward.wildgoose at
Sun Mar 23 20:23:13 UTC 2003

> Thanks, adding gbuffers=16 helps considerably.  But, gbuffers=32 just
> mythfrontend.  It still appears as if it is dropping frames in both rtjpeg
> 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
> to gbuffers=32 on the web and people seem to have success.  Not me.  Any
> 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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