O2 Framedrops
Kurt Volker Krieg
I've just upgraded my O2 with an A/V Board.
When I record a movie with dmrecord or mediarecorder via composite in, it
occasionally drops 1 or two frames. Sometimes it seems like that it looses
sync on the video signal, so that within the movie it seems that 2 frames
are shown simultaniously. This is when capturing from a VCR. Works like a
charm with a signal coming from a satelite receiver.
Any ideas?
SkyWriter
> Hi,
>
> I've just upgraded my O2 with an A/V Board.
> When I record a movie with dmrecord or mediarecorder via composite in, it
> occasionally drops 1 or two frames. Sometimes it seems like that it looses
> sync on the video signal, so that within the movie it seems that 2 frames
> are shown simultaniously.
I believe that when it does drop a frame it duplicates the previous frame.
> This is when capturing from a VCR. Works like a
> charm with a signal coming from a satelite receiver.
try less quality when capturing.
>
> Any ideas?
Avi Bercovich
Nope, but I;d like to add that I've seen similir things happen on my
O2's (but r5k and r10k) when recording from VHS VCR tapes. No problems
what so ever when using a DVD player. (other than the known 6.5.14
(m)jpeg issues)
ttfn,
avi
Michael Rice
The issue of dropping frames is addressed in the mediarecorded(1) man
page. It specifically mentions that recording from a VHS may degrade the
video signal enough to cause frame drops. It also offers some potential
solutions.
When a frame is dropped, the previous video frames are repeated. So you
end up with a slight (and hopefully very short) loss of motion when
you playback the recording.
Michael Rice
<snip>
>
> The issue of dropping frames is addressed in the mediarecorded(1) man
Should be "... mediarecorder(1) man..."
mike
Same problem here - recording from VCR seems to give me many problems - either
the tape is old and jerky in a few spots and always results in dropped frames
(for example - me trying to capture old gijoe cartoon movies from VCR tapes
that are like 20 years old) or there was a spot where the screen turned white
from dark real quick - for example - a recording of my band playing a club
(dark lighting) where people where using flash photography - always dropped
frames in the same spot of great flashes.
same results if I use dmrecord or mediaplayer. I can not capture anything if
the frames are dropped - once a frame drops, the rest of the movie/caputre is
basically ruined - I see two frames interposed together for the rest of the
movie, or I see strange horizontal lines transposed through out the rest of the
movie. This seems to happen 99% of the time after a frame is dropped and I
keep recording. I thought I might have a bad A/V module - but now I dunno...
(I was planning on making a web site about capturing video with o2's and
various ways around these problems... I still might do that).
There seems to be two solutions to recording from VCR that I havent tried. One
would be to use a device called a TBC, (time based correction ?) which would
help the o2 capture video with a stabilized sync.
The other method that might work is plug up another video device between the
VCR and the o2 (kinda like a TBC, but not a TBC) so even though the signal gets
degraded, the lower voltage might not mess up the o2 to the point where it
losses sync and drops a frame. I havent tried any of these two methods yet,
but any out there - please comment!! :)
I probably wont try a TBC because I hear they are too expensive for a hobbyist
like myself :)
cheers!
mike
Emmanuel Florac
dit...
>
> There seems to be two solutions to recording from VCR that I havent tried. One
> would be to use a device called a TBC, (time based correction ?) which would
> help the o2 capture video with a stabilized sync.
TBC = Time Base Corrector. It is intended to correct exactly this kind of
problems...
> The other method that might work is plug up another video device between the
> VCR and the o2 (kinda like a TBC, but not a TBC) so even though the signal gets
> degraded, the lower voltage might not mess up the o2 to the point where it
> losses sync and drops a frame. I havent tried any of these two methods yet,
> but any out there - please comment!! :)
>
Professional VTRs (Betacam SP BVW series...) have a built-in TBC, so
passing thru it corrects the signal. Some professional VHS VTRs from JVC
also have it.
--
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Emmanuel Florac | Kreode technologies
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Martin Slaney
Avi Bercovich wrote:
Sure - thats to be expected. A VHS machine is likely to output some pretty wacky
unstable sync signals. If you play in the VHS via a TBC (time-base corrector)
you'll likely find its perfect .....
Alexis Cousein
> This is when capturing from a VCR. Works like a
> charm with a signal coming from a satelite receiver.
>
That would suggest you need a timebase corrector to get a clean
signal from the source that doesn't work.
Incidentally, try to see if changing the "VTR mode" and "Auto Gain"
buttons on the Video Control Panel's Svideo Input-Signal panel
helps (sometimes changing aperture and bandpass freq. helps, too).
--
<these messages express my own views, not those of my employer>
Alexis Cousein Senior Systems Engineer
SGI Belgium and Luxemburg a...@brussels.sgi.com