[MPlayer-users] mencoder options for NTSC television

[D Richard Felker III]

On Fri, Jan 17, 2003 at 08:41:11AM -0600, Lance Simmons wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> On Tue, Jan 14, 2003 at 01:16:47PM -0500, D Richard Felker III wrote:
> > On Tue, Jan 14, 2003 at 10:20:58AM -0600, Lance Simmons wrote:
> > > 
> > > But can't I do _better_?
> > 
> > Yes, you can. At such a high bitrate you're going to want to re-encode
> > to a smaller file later anyway, so here's what I would do:
> 
> Thanks! That's very helpful information.  The results are impressive.
> 
> The one thing I'm still not sure about is the resolution I should use.
> You suggest 640x480.  Why?  What's the relationship between the NTSC
> standard and the resolution one chooses? 

NTSC has 480 lines (visible), and 640 is the corresponding width that
will give you square pixels for a 4:3 aspect picture. While horizontal
pixels are something of an artificial notion with television (you're
actually dealing with a continuous band-limited signal), vertical
lines are discrete objects, so capturing at a resolution other than
480 isn't a matter of sampling at a different rate, but rather
digitally blending lines and whatnot. Normally this will reduce
quality, especially when done by the naive algorithms used in low-end
hardware.

As a special case, if you capture at 240 lines or less (half
resolution), most cards will capture individual fields rather than a
whole frame at a time (fields are halves of interlaced frames,
consisting of just the even or just the odd lines). So capturing at a
height of 240 can have its benefits, since you don't have to
deinterlace and the card doesn't vertically rescale the frame. (And of
course it saves lots of cpu time just by giving less data to
compress, too!)

> I guess this is a general question, not really about mencoder -- I
> wonder if there's something somewhere online I could read that explains
> this in more (but still non-technical) detail.

The mplayer list archives and the files in DOCS/tech might be helpful.
You could also search for NTSC introductions and stuff on the web.

Rich