[MPlayer-users] Interlaced video replay as interlaced video with mplayer

[D Richard Felker III]

On Thu, Feb 19, 2004 at 07:24:38AM -0500, widgital at pop3.demon.co.uk wrote:
> Hi there - first post on this mailing list - so apologies for incorrect
> netiquette, or posting in the wrong place.
> 
> I was referred here by the developers of the Xbox Media Center - which I
> believe incorporates mplayer for video replay?  
> 
> I was hoping to use XBMC as the front-end of a DVB-T/DVB-S MPEG2 (but also
> Divx and MPEG4) PVR and video server system.  The XBox looked like a nice,
> low cost, flexible platform, with high-quality RGB output to a European
> SCART TV.
> 
> However on further analysis it seems that the XBMC currently only replays
> interlaced video (such as MPEG2 DVB recordings, and video sourced DVDs) by
> de-interlacing to progressive and then re-interlacing for display on a TV. 
> This works OK - but there is a quality loss involved in de-interlacing and
> re-interlacing - which seems a little sad.  Some people have reported
> partial success with interlaced replay using Xbox Media Player (older
> builds) using no post-processing, but the AV sync process seems to lock to
> the incorrect field order 50% of the time (producing movement judder)
> 
> The XBMC guys said they thought mplayer can't replay interlaced material as
> interlaced - it has to convert to progressive internally.  Is this the
> case? Is it possible to "fudge" things - so interlaced material is
> converted to progressive with no processing (so the frame appears to be
> full of combing artefacts on motion) - but with fields guaranteed to be in
> the right order within the frame, so that when the frame is read out as
> interlaced (if it can be) the fields automagically re-appear?
> 
> I have been reading quite a few posts on various mailing lists - and some
> people detail success with some video cards (Matrox?) using fieldparity
> options and no pre-/post-processing to ensure clean replay of interlaced
> fields, with no scaling or de-interlacing. (So the recorded fields are
> output in the right order?)
> 
> Is this the case - if not is anyone aware of a solution that will provide
> clean interlaced replay that might be applicable to mplayer - either with
> an Xbox, or using a cheap video card in a small form factor PC. The key
> thing is to support RGB output at 15.625/50 - not composite or S-video via
> a TV out line/field-scan converter?
> 
> All help/advice gratefully received.  Again apologies if this is the wrong
> place.
> 
> I realise that most of the end-users of mplayer are more interested in
> replay of non-interlaced Divx and MPEG4 stuff, or de-interlacing MPEG2
> interlaced material for replay on progressive (i.e. VGA PC) screens.
> However if someone can point me towards to a solution I would be a very
> happy bunny!

In principle, as long as your vo driver syncs to vertical blank, you
should just be able to play the file as-is and have it show up right
on an interlaced display. However, if the timing ever gets off at all,
you'll see nasty jumps 'back in time' for a split second. You should
test it yourself and see if your system's performance is stable enough
to keep this from happening.

Rich