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

[Adam Nielsen]

> Some days ago (16/12/2003 exactly) a thread called "converting 25fps -> 
> 23.976 fps?" talked about using the -speed parameter.
> Now the video plays smoothly as silk, and it's great.

Yes, the difference between 23 and 25fps is so small that playing the movie a 
little faster/slower won't be noticable.

> 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?

Without the -speed parameter is the correct movie duration, however you're 
slowing down the movie by running it at 25fps, and then speeding it up again 
by using -speed.  So in this case *with* speed should be the correct 
duration.

> 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?.

Yes, that is correct.  It will also be slightly higher pitched, however the 
difference will probably not be very noticable.

> 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).

Yes, the sound is slowed down because you're playing the whole movie slower.  
It's actually very complicated to adjust the speed of the audio while 
retaining the same pitch, but even so, going from 30fps -> 25fps would be 
quite noticable because the people will be talking slower.  Is there some 
reason why you can't switch to NTSC output?  If you run the dxr3 in NTSC mode 
it will output at almost 30fps so you won't need to adjust the speed and it 
will still play smoothly.

> Can someone explain this a little better? Is there a way to fix this? Is 
> there a better way to correct this "glitches"?

Everything you've said seems to be correct, I'm not sure if there's another 
way to fix the problems - I can't remember whether the dxr3 can run at a 
different framerate and do the conversions automatically (you could try 
playing the files under Windows and see if they're smooth there.)

> If this is the only way to fix the problem, I think it must be in the 
> manual.

It's probably not the only way, but it's by far the easiest.  You could 
theoretically resample the frames to bring them to 25fps, and resample the 
audio to match as well, but the effort required would not really be worth it.

Cheers,
Adam.