[MPlayer-users] How to tell if the video input is interlaced or not?

[Rich Felker]

On Fri, Dec 16, 2005 at 09:25:30PM +0200, Jouni.Lohikoski at iki.fi wrote:
> On Thu, Dec 15, 2005 at 04:47:07PM -0800, RC wrote:
> > It only works without X?  That really doesn't make any sense to me.  I
> > can't think of any reason a capture card would stop working when X
> > starts.
> 
> Something to do with DMA access and how they changed xv driver from old
> XFree86 to Xorg's current one. It just do not work if X has been even
> visited during the boot session.
> See:
> http://sourceforge.net/mailarchive/forum.php?thread_id=9003225&forum_id=34082

Disable support for the TV card in the X server by removing the v4l
module. Then X should not interfere with it.

> > I think you can safely assume (PAL) TV is always going to be
> > interlaced.
> 
> Also assume same for any PAL capture card?
> And as the driver/chip can output 576 lines, why cannot I assume it does
> de-interlacing itself?

Because deinterlacing is incorrect. TV capture cards (most) output
pairs of fields interleaved together.

> And if I then capture 288 lines (height) 50 times in second, I should
> deinterlace by mplayer and somehow convert it to from 50 fields per sec
> to 25 FPS?

Most cards do not support this, and mplayer does not support it
either. And no you should not halve the framerate. That just makes
your video into crap.

> In tv-input.html:
> "If you capture the video with the vertical resolution higher than half
> of the full resolution (i.e. 288 for PAL or 240 for NTSC), make sure you
> turned deinterlacing on. "
> 
> The above quote isn't quite clear. Why if the capture-chip and the
> driver already provides 704x576 "images" to the application, 
> they should be deinterlaced? 

It's stupid advice. It should say: "If you capture the video with the
vertical resolution higher than half of the full resolution (i.e. 288
for PAL or 240 for NTSC), then the 'frames' you get will really be
interleaved pairs of fields. Depending on what you want to do with the
video you may leave it in this form, destructively deinterlace, or
break the pairs apart into individual fields."

Rich