Dieser Artikel wurde als Tutorial für das Videoportal Vimeo geschrieben und ist deswegen auf Englisch!
Why converting 25fps to 24fps?
As you can read in the Vimeo HD FAQ, the Vimeo encoder auto-converts HD videos to 24fps maximum. If you come from a PAL zone like me, this can be a problem, because even the PF/P/cinema/whatever-modes of our cameras produce 25fps.
Framerate conversion is always a pretty messy job. It’s not fair to give it to a converter made for processing many many videos per hour like the Vimeo encoder. It gets the job done, but not always with the best results. The video starts to jump or stutter, like there is a frame missing now and then.
Free software to the rescue!
Powerful editing suites like AFX have motion interpolation algorithms which can lead to really good results, but there are also a few freeware choices to change or convert fps. In this article I will show you how to do it with VirtualDub. You can download this software for free at SourceForge. If you already have VirtualDub, make sure that your version is not too old, or you will not able to use advanced audio filtering.
Everything set up? So let’s start!
Open your file in VirtualDub. In the Video tab, activate Direct Stream Copy. That tells VirtualDub to not recompress your video when you save it later. From the same tab open the Frame Rate dialogue, and enter in the Change Framerate to field enter 24.
Because your video now plays 4% slower, you also need to make the audio track 4% longer. This is called Time Stretch in VirtualDub. To do this, go to the Audio Tab and activate Full Processing Mode and Use Advanced Filtering.
Now open the Filters dialogue. The windows works very similar to GraphEdit – click on Add and add the filters Input, Time Stretch and Output. If you add the filters in this sequence, VirtualDub will automatically build a working filter chain.
Looks nice, but doesn’t do a thing so far. So double-click on the Time Stretch box and enter 1.04 in the Time ratio field.
Your audio track matches the video track again, you are nearly done! The audio track needs to be recompressed, so don’t forget to set a select a codec in with Compression in the Audio tab. If you only have the default MPEG Layer 3 codec installed you might want to google for an uncrippled coded like LAME.
Now choose Save as AVI from the File dialogue, wait a few minutes while VirtualDub is working, upload the new file to Vimeo and enjoy a smooth HD video.
should be 1.0417 and not 1.04 (1 divided by 24 instead of 25)
thanks for the guide
Yes, you are right. Just because 24 divided by 25 is 0.96 doesn’t mean that 25 divided by 24 has to be 1.04. ;)
1.0417 or 1.041 period 6 is more exact and should avoid syncing problems in long videos.