[MEncoder-users] Determining proper frame rate

Chris Capon ttabyss at gmail.com
Sun Dec 27 19:06:39 CET 2009


On Wed, Dec 23, 2009 at 12:47 AM, Laine Lee <llee040 at sbcglobal.net> wrote:

>
> On 12/13/09 9:37 AM, "Chris Capon" <ttabyss at gmail.com> wrote:
>
> > One way to get 30 fps from telecined content seems to work if you are
> > using the -of mpeg encoder.
> >
> > Use filmdint=io=30:24 -ofps 24000/1001 then add the -mpegopts telecine
> > parameter.  This produces output which is encoded at 24 fps but then is
> > soft scaled to 30 fps when played (so the output size stays the same).
> > This allows telecined content to play on older DVD players which may not
> > support 24 fps.
>
> I've tried that telecine option, but nothing I feed the resulting video
> into
> sees it as 30 fps. The DVD players say 24, mediainfo says 24, QuickTime
> player says 24. I don't understand why. Does the command option have other
> requirements? I mean if the output of a command that employs that option is
> 30, it should be obvious, right?
>
> Hi Laine:

I'm not sure about other players, but the effect of the telecine flag can be
seen using MPlayer.  When I play back content encoded this way, MPlayer
reports:

    VIDEO:  MPEG2  720x480  (aspect 3)  29.970 fps  9800.0 kbps (1225.0
kbyte/s)
and:
   demux_mpg: 24000/1001fps progressive NTSC content detected, switching
framerate.


My understanding may be off the mark so its a good idea to check with others
(I'm still new to MPlayer and MEncoder), but here's what I think is
happening.

In the MPlayer source file /libmpdemux/video.c, if you search for "telecine"
and "MSGTR_EnterTelecineMode" you find code that appears to check frame
display times against the encoded frame rate.  If they don't match, then it
tries to adjust the amount of time each frame is displayed by a factor of
5/4 (or 4/5 depending on your viewpoint).  I think this has the effect of
playing 24 frames at a rate of 30 fps (with 1 in 4 frames being repeated).

I'm guessing that the job of the telecine flag in mencoder is to adjust the
time stamps on 24 fps content so that it plays back at 30 fps.  The benefit
is content encoded at a lower frame rate but which plays back at a higher
frame rate.

In my case, before using the telecine flag, 24 fps telecine content would
not play on two older DVD units.  After applying the telecine flag the
content played on them both.

The effect may not work on media players other than MPlayer, but it does
seem to help older DVD players and will also play properly on new DVD
players.

Hope this helps,
Cheers,
Chris.


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