[MPlayer-users] Q on monitor refresh rate versus fps

[Matyas Sustik]

Hi All,

I do not understand the connection between monitor refresh rates and movie
fps.  I read a few posts available in the archives but I would appreciate
if someone could give me an unambiguous answer to the following questions.

1.  When I play a 24fps source, how will the frames be displayed on a 60Hz
refresh rate monitor?

2.  Should one sync the refresh rate to the video fps?  (Multiple?)

3.  What does mplayer do different when playing the same video source, on
different refresh rate monitors?

4.  When purchasing an HDTV (1080p) does the 120Hz refresh rate get me
anything worth paying for?  Note that I may be forced to use the TV through
the VGA port since the PC-TV HDMI handshake protocol may not work.  (Oke, I
never got it to work with my current unit despite my best efforts.)

My questions are triggered by observing the playback of various video
sources.  In particular I have a DVD (Love in the Afternoon) which appears to
have progressive frames when I play it frame by frame (using '.').  However,
every 4th frame is repeated, that is the fifth frame is the same as the
fourth frame.

The movie is marked 29.97 fps so I figure that the original was recorded in
24fps and then to display it as 30fps every 4th frame is repeated (4/5 =
24/30).  I guess that then to use the 60Hz refresh rate every frame (included
the duplicated ones) are shown twice by the hardware.

What program is doing the frame duplication?  Is it mplayer figuring out my
refresh rate and repeating the frames?

The above was observed on a 1600x1200 at 60Hz monitor.  Then I played the source
on an 1920x1080 at 50Hz HDTV.  (xrandr returns 50Hz, as well as the TV menu.)
When I played the movie frame by frame, again I saw every 4th frame repeated!

Of course that does not mean that in continuous play the same thing happens.
 In fact I am very curious whether that is the case or not.

I am afraid that the frame duplication is somehow encoded in the mpeg stream
and always happens, kind of assuming that everyone has a 60Hz refresh rate
display device.  In that case though that would mess up on my 50Hz TV.  I
checked the play time and it is identical on both the 60Hz and the 50Hz
displays.  I must be very confused I guess.  Any insights on the above would
be greatly appreciated.

I reencoded the movie using x264 and the result again shows the repeated
frames.  A side question is that how the duplicate frames get stored?  Is
there just a flag indicating that there is a duplicate?  The duplicates may
actually hurt compression, but I am not sure.  In any case I would prefer to
encode the movie as 24fps and do the frame duplication on playback only when
the monitor refresh rate requires it.

Thanks!
Matyas
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Every hardware eventually breaks.  Every software eventually works.