[mythtv-users] What don't I get here? (Interlaced playback...)
hobbiticus at gmail.com
Thu Jun 14 17:12:25 UTC 2007
Your analysis about framerate is correct. You can get the "full pseudo 50
fps" framerate in two ways.
The easiest way is to use bob deinterlacing. All of the other deinterlacing
methods included with mythtv by default combine both fields of a frame and
output at 25 fps. You can configure this in your tv->playback settings
within the frontend. However, bob deinterlacing can be computationally
intensive, and may be too much for a 1Ghz processor - you'll have to try it
yourself and see how it handles.
The more difficult, but sometimes better, way of doing it is to use an
interlaced output mode on your video card and turn off deinterlacing in
mythtv. This will allow your TV to do the deinterlacing, and is equivalent
to plugging your cable directly into your TV. However, this involves
playing with your X config, and I can't really help you with that because I
can't get it to work on my hardware either.
I'm not sure what inputs are available for PAL TVs, but for standard
definition, S-Video will usually give you the best picture. It is
definitely better than the standard RCA A/V composite hookups
(yellow/red/white jacks) that are found on NTSC TVs. Also, any conversion
of the input between different types of jacks is prone to slight signal
On 6/14/07, Steve Smith <st3v3.sm1th at gmail.com> wrote:
> System summary:
> Dual P3 1Ghz
> 1Gb RAM
> Nvidia 5200 -> S-VIDEO to CRT PAL TV (PAL)
> Recordings are DVB-T or PVR-150 sourced from Antenna or Composite video
> (Telewest Cable box)
> So basically I'm playing Interlaced PAL SD @ 50Hz recordings through the
> TVOUT of my nvidia.OK?
> So what I don't get here is:
> Why does the framerate look slow in comparison to
> a) actual live tv e.g. straight from cable box to TV
> b) One of my mpegs played back through my MediaMVP?
> (What I mean is movement looks just slightly blurred and jerky)
> I've done some diagnostics using mythfrontend -v playback and I'm getting
> a solid 25fps....
> So that leads me to the following.....
> 1) "Normal" TV is rated at 25 frames per second but as it's interlaced it
> actually 50 FIELDS per second.
> 2) The two fields that make up one frame often contain some movement
> (otherwise we wouldn't have the de-interlace problem to sort out would we?)
> 3) THEREFORE "Normal" Interlaced TV actually has a pseudo 50hz frame rate
> (albiet they're not really full frames but sort of half resolution).
> 4) So if my player deinterlaces and plays at 25fps we actually get a
> reduction in perceived frame rate and hence the slight jerky/blurriness in
> comparison to live TV.
> So am I correct in my analysis? Is the mythfrontend actually playing 25
> full frames a second or 50 fields a second?
> How can I get the "correct" output of 50 fields a second where
> potentially the two fields in each frame can contain movement?
> Would using a CRT output (RGB to SCART) instead of S-VIDEO help? (in this
> respect not just overall quality) i.e. is the NVidia TV-Out doing
> something to the timing...e.g. insisting on using 60hz without telling me
> thus throwing out the timings, or maybe even forcibly de-interlacing the
> mythtv-users mailing list
> mythtv-users at mythtv.org
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