[pvrusb2] Bottom Border Video Artifact Problem

Mike Isely isely at isely.net
Sat Feb 27 10:36:44 CST 2010

On Wed, 24 Feb 2010, Bob Freemer wrote:

> Thanks, Mike for all your hard work on the driver.  It's quite a piece of
> engineering.
> I have video capture working great (system info below) with one exception.
> A small line (a few pixels or so) of garbled pixels shows up in all my
> captures.  The line appears to me a digital artifact (looks like when stream
> is lost).  It only shows up at the bottom as I say, and does not affect
> other parts of the video.  This line appears when capturing from RCA inputs
> (I haven't tried the tuner) and NTSC.  I've verified it appears with
> multiple video sources, so is unlikely a problem with the analog input
> signal.
> Of course I could crop it out in post-processing, but I wonder if there is a
> setting that may correct this?
> I've reviewed all the postings on this list and gone through all the
> ctl_video parameters without finding anything that looks promising.
> Any suggestions?  I could certainly attach a capured frame if attachments
> are allowed on the list.

The V4L API includes the ability to control cropping within the video 
digitizer.  However even though the API is present, it has to be 
implemented by the driver that runs the digitizer.  In the case of a 
24xxx or HVR-1950/HVR-1900 device that's cx25840.ko.  For a 29xxx 
deivce, that would be saa7115.ko.  Unfortunately the API is *not* 
implemented in either case.

There is one subscriber to this list who has circulated patches to the 
cx25840 module to implement the capability there, but I am not the 
authority on how that chip works so I haven't been comfortable taking on 
the responsibility for the changes - the cx25840 driver is not my area 
of expertise.

There are already changes in the pvrusb2 driver to make that API 
available to applications (the driver just passes the information 
through).  Admittedly there's one more minor change I need to dig up 
and apply (I keep forgetting about that one, damnit).



Mike Isely
isely @ isely (dot) net
PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8

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