[MPlayer-users] 2 questions about 2-Pass DivX encoding with mencoder

[Troy D. Strum]

Whee, lots to read - thanks Tim.

DVDs can be in multiple formats (like VCD) that includes 29.970 and 23.976
(film) and 25 for PAL. Would it be safe to bet that if the original source
material is video then it's safe to assume the output should be 29.970?

As well, if you drop to the lower framerate with -ofps 24 (or would you go
to -ofps 23.976 ?) the telecine just magically goes away? AFAICS lowering
the framerate alone won't remove the pulldown without some help...

(my brain hurts)


- Troy



----- Original Message -----
From: "Tim U." <mplayer at tetro.net>
To: <mplayer-users at mplayer.dev.hu>
Sent: Tuesday, January 08, 2002 10:12 AM
Subject: Re: [MPlayer-users] 2 questions about 2-Pass DivX encoding with
mencoder


[Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
On Tue, Jan 08, 2002 at 11:28:06AM -0400, Troy D. Strum wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi folks...
>
> (I'm using the 0.60 release)
>
> When I encode a video using the two pass method I know I can safely delete
> the AVI file from the first pass. Knowing this, can you just send that
first
> file into /dev/null or something? ...or would this have little positive
> impact?

I do exactly that, simply to save disk space.  It would be nice to have a
-ac null option so that no time is spent decoding or encoding the audio on
the
first pass.  The only reason I can think of to keep the first pass AVI is to
check if the video looks all right before starting the second pass, since,
unlike with Windows encoders, the first pass AVI produced by mencoder is
playable.

> Secondly, I caught some mentions of NTSC DVDs having issues. I ripped The
> Prisioner box set (4 titles in total) with no problems (NTSC, 29.97fps)...
> am I just lucky or is there something else I should be on the lookout for?
> (I noted some brief discussion on -ofps but would like some more info)

I have noticed problems with most NTSC DVDs (the only kind available to me),
all are problems with the inverse telecine, or 3:2 pulldown (pullup?), or
whatever you want to call it.  Usually it is noticable in just one or two
scenes, sometimes a lot more.  You're supposed to use 23.976 FPS when
encoding
29.97 FPS NTSC DVDs, because thats exactly the frame rate you get when you
take
away the duplicated fields.  For a good explination of telecine, read:

http://www.divx.com/support/guides/ntsc_pal.php?cid=1&gid=3

When the movie is not completely inverse telecined, you have too many video
frames, and that can cause the video to fall behind the audio, with the
delay
increasing as more frames that weren't inverse telecined are played.  A'rpi
recommended that I use the option "-mc 0" once, to prevent A-V sync
correction.  I guess without that option the audio would not get out of
sync,
but the non-inverse-telecined frames would still be there.

mencoder has inverse telecine problems with "War Games" and "The Saint", and
probably others that I can't remember right now.  I also tried encoding
those
movies in Windows using mpeg2avi, and DVD2AVI->VFAPI->VirtualDub.  Using
DVD2AVI->VFAPI->VirtualDub produced the exact same inverse telecine problems
as mencoder.  mpeg2avi produced less inverse telecine problems, but still
enough that I didn't want to save the AVI.  The quality of the video
produced
by mencoder is also noticably nicer looking than that produced by VirtualDub
and mpeg2avi, but maybe that was due to some option I didn't choose.

I hope you can find something useful in my reply.
   - Tim U.