does 23.97fps output = 23.976fps?

Org Profile · Post by **808-buma** » Mon Mar 12, 2007 7:46 pm

Hey all,
stupid question time - from my editor (Magix Movie Edit Pro 10) I export my AVI files as 23.97 to match my original input files. To make mpeg files, I usually take the AVI file to TmpegEnc and then save it as a 23.976fps mpeg2 file. So, it got me to thinking...

So, I've gone back to my editor and tried exporting it at 23.976fps, but it just rounds off to 23.97 again.

So, question is: for all intensive purposes, is 23.97 = 23.976 or am I just stretching out my vid file still when I try encoding my native 23.97fps AVI file as a 23.976fps mpeg file?

mostly this is just a 'who the hell cares' question, but meh, I was just curious...

Thanks in advance!

Scintilla · Post by **Scintilla** » Mon Mar 12, 2007 8:01 pm

Suggestion: Take one of the exported files into VirtualDub(/Mod) and check its file information to see what the frame rate really is (VirtualDub displays it to something like 6 decimal places).

Zarxrax · Post by **Zarxrax** » Mon Mar 12, 2007 8:04 pm

Magix wont go to more than 2 decimal places. You are probably a little bit better off going with 23.98 than 23.97.

Org Profile · Post by **808-buma** » Mon Mar 12, 2007 9:06 pm

scintilla - taking my clips into VDMod like you suggest, the source avi files from my dvd do show as 23.976 and my Magix export AVI file show 23.97...

zarxrax - hmmm never thought of that. So, instead of being .006fps off, I'll be .004 frames ahead?

so, say for a 3 minute file:
23.97fps x 180s = 4,314.6 frames
23.976fps x 180s = 4,315.68 frames
23.98fps x 180s = 4,316.4 frames

so if 23.976 = the "0" point:

Code: Select all

23.97fps-------------23.976fps-------------23.98fps 
1.08 frames off----0 frames off----plus 0.72 frames

so... what does it all mean then? Is it better to make it slightly longer and 'squeeze' AVI down to fit rather than 'stretch' the file to make it fit? I mean, for the 'average' video of 3 minutes, does it make any difference? Or am I doing something wrong?

Just curious...

Gods Dark Angel · Post by **Gods Dark Angel** » Fri Mar 16, 2007 2:13 pm

This sounds like an awful lot of work for just a lil more or less than half of a thousandth of a frame. Especially if your already at .976 Does it have to be right on point?

Scintilla · Post by **Scintilla** » Fri Mar 16, 2007 3:22 pm

Gods Dark Angel wrote:This sounds like an awful lot of work for just a lil more or less than half of a thousandth of a frame. Especially if your already at .976 Does it have to be right on point?

It does if it turns out that the fractional difference causes the A/V synch to be lost by the time the viewer gets to the end of the video. Which may or may not be the case, depending on a number of factors.

If the synch looks okay the whole way through the video, then I'd say don't worry about it. If you really need the video to be exactly 23.976fps for some reason, you can always hit it with <b>AssumeFPS(23.976,true)</b> in AVISynth, which will make sure the audio stays synched properly.

Willen · Post by **Willen** » Sat Mar 17, 2007 7:16 am

The longer the video, the more pronounced the sync difference will be.

For a 3 minute (180 second) video:
23.976 fps x 180 s = 4,315.68 frames
23.970 fps x 180 s = 4,314.60 frames <-- nearly 1 full frame off faster
23.980 fps x 180 s = 4,316.40 frames <-- almost 1 frame off slower

Extend it to 6 minutes (360 seconds):
23.976 fps x 360 s = 8,631.36 frames
23.970 fps x 360 s = 8,629.20 frames <-- a bit over 2 frames off faster
23.980 fps x 360 s = 8,632.80 frames <-- almost 1.5 frames off slower

I didn't trust Magix's handling 23.976 fps footage with precision so when I edited my FLCL video, I did it by adjusting clips to 24 fps first like EADFAG outlines for Premiere 24 fps editing. I edited with 24fps sped-up audio, then I adjusted the final export back to 23.976 fps in post. I muxed the original non-sped-up (23.976 fps) audio back in during the XviD compression stage.

Org Profile · Post by **808-buma** » Mon Mar 19, 2007 6:16 pm

crap, Willen...

I guess my vids aren't quite as sync-dependent as your vids are then

as I haven't had a problem as of yet... I just sorta noticed that as I was trying to output my vids for the cons and their 23.976 fps formats when I made the discovery...