[mythtv-users] Live TV and Recorded TV playback question

[Len Reed]

Sean McLachlan wrote:
> I have an odd Live and recorded TV playback issue.  DVDs play just fine.
> 
> When I slow the playback down, I can see 3 frames of clear video, then 2 
> frames of what appears to be blurred, de-interlaced video.  I'm kind of 
> a newb here, so I'm probably screwing up my terms, sorry.  The bad 
> frames look like 2 images that have been combined.  If the subject is 
> moving his hand, you can see his hand faintly in 2 places for 2 frames, 
> then the next 3 are fine, the next 2 are blurred, next 3 are OK, etc.

You're looking at telecined video under NTSC.  That produces exactly the 
pattern you're seeing if you view it frame by frame.  It has nothing to 
do with V-Sync.  This is just how movies are show on standard NTSC 
television, where they have to stretch film's 24 frames per second into 
30 frames (which, interlaced, is 60 fields).  They deliberately combine 
the film's frames so that 2 of 5 frames video frames have half of one 
film frame and half of another.  When the source material has motion, 
including camera panning, this is quite noticeable.

See http://en.wikipedia.org/wiki/Telecine

That has a really nice picture showing how four film frames A, B, C, D 
get interlaced.

I don't see why things should look worse when viewing full speed from 
myth than they do just watching TV directly, though, since the the 
telecine interlacing is in the source TV signal.

I'm not sure if turning on deinterlacing will help, since things will 
need to get re-interlaced to go out the S-Video port.  It might result 
in frame doubling (which is how a progressive scan DVD player does 
things) instead of telecine.  If you had a high def TV, though, and were 
using DVI or component video, then you definitely should turn on 
deinterlacing.  You said you were using a plain old TV, though.