[MPlayer-users] About 23.98 -> 25 fps (and others) framerate conversions

[Julián Nuñez]

Hi.
I don't know if this mail belongs here or in dev-eng, I'll just drop it 
here.

I will share some experience with playing different framerate movies at 
25 fps, and some things I don't understand.
I'm a DXR3 user, and been using it for a half year now with mplayer, I'm 
a mplayer user since 0.60.

I use my DXR3 in PAL norm, wich is 25 fps and since the beginning I 
noted this "glitches" or -very- tiny pauses once per second with movies 
encoded at 23.98 film framerate (most of them).
This "glithes" are the only problem I suffer, A-V sync and image quality 
are both perfect. The problem is not present when I play 25 fps movies, 
but those are rare.
Having tried every posible solution without success (changing FPS value 
en lavc, disabling sound, every posible autosync value, compilers, 
mplayer versions) I gave up.

Some days ago (16/12/2003 exactly) a thread called "converting 25fps -> 
23.976 fps?" talked about using the -speed parameter. I think Rich 
mentioned that. I tried that and...it worked! the command line was:

mplayer -vo dxr3 -vop lavc,expand=-1:480:-1:-1:1 -speed 25/23.978 movie.avi

Now the video plays smoothly as silk, and it's great.
This is what I think was happening: This glitches are the last frames 
from every second staying twice the time, to "fill" the last 25th PAL frame.
What I think -speed 25/23.978 does is put a frame from the next second 
in the last of the 25 frames, playing the video at 25 fps but faster.

Now, my questions (finally):
If I'm playing the video faster, it will take less to finish... this is 
logical since this "pause" every second causes the movie to last longer, 
so , which duration is correct, with or without the -speed parameter?
Also with the -speed parameter the sound changes it's hz, going from 
48000hz to 52000 or so. Does this mean the sound is played faster? I 
think so, it will be leaved behind othewise, am I correct?.
With a 30 fps movie, instead of this "tiny pauses", the video goes very 
fast in the end of every second, I think those are the spare frames 
caused by 30->25 fps conversion, so I've tried -speed 25/30, and the 
video plays GREAT, but now the sound is slow, everthing is lower tone 
(played at 36000 hz).

Can someone explain this a little better? Is there a way to fix this? Is 
there a better way to correct this "glitches"?.
If this is the only way to fix the problem, I think it must be in the 
manual.

Thanks for your time.
Julian.