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You are here: MacNN Forums > Software - Troubleshooting and Discussion > Applications > Adjusting 25fps video to 24fps

Adjusting 25fps video to 24fps
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tooki
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Sep 6, 2009, 03:22 AM
 
So you video pros out there surely know how movies (and most TV shows) are shot at 24fps. And you probably know that for PAL release to DVD/tape/TV, they leave the frames alone and just play it 4% faster at 25fps, so both the runtime is wrong, and the audio pitch is too high.

Any ideas how to slow it back down to its native 24fps and slow the audio down again, too? If there's a simple way to do it without having to re-encode, so much the better!

(Or if there's a way to fix it in HandBrake in the future during transcoding, that'd be good to know.)

Thanks!
     
mduell
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Sep 6, 2009, 04:46 PM
 
2:2 pulldown is what you're looking for. I think Handbrake can do it.
     
tooki  (op)
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Sep 7, 2009, 12:32 PM
 
No, that's something else (taking 50Hz interlaced and making 25fps progressive out of it).

What I need, in essence, is a way to edit the headers of an h.264 file to make it think it was recorded at 24fps, so it plays 24 frames in a second. Plus the audio needs to be synced (but not pitch-corrected; the pitch needs to fall with the frame rate!!!).
     
P
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Sep 7, 2009, 05:29 PM
 
I think they correct the audio pitch of the music these days - probably just desyncing it from the video. There is a definite difference in TV shows from today and those from the eighties or thereabouts - the music in the old shows makes me wince.

Anyway: FFmpegX can change the framerate, but it will not keep the audio in sync (there's even a warning about this in help file). Possibly you can strip out the audio, adjust its speed separately (Google shows a bunch of tools that can do that) and add it back to the video again, but your idea about manipulating headers certainly sounds easier. Never heard of a tool that will let you do that, though.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
ghporter
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Sep 7, 2009, 06:41 PM
 
From what I've read, instead of de-syncing the audio, higher-end (broadcast) applications use a frequency shifting technique to restore the audio to its correct pitch.

Glenn -----OTR/L, MOT, Tx
     
direktor
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Sep 10, 2009, 02:31 AM
 
Tooki,

Cinema Tools does what you want (it's called conforming a piece of media). "Conforming" is a term used in different ways in post, so be careful when googling this...people talk about conforming in different contexts and it means different things.

The problem is that CT will only do it on media/codecs intended for editing in FCP, and even then some are left out. DV, DVCPRO, DVCPRO HD, ProRes variants can all have the QT headers re-written to playback at different speeds. HDV files, H264s, MPEG2 files cannot. I assume this because of the nature of MPEG2 and 4 files.

If I were you I'd trancode your H264 to a very high quality ProRes, and then re-encode back to H264. A pain, I know.
     
Bad Cyborg
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Sep 11, 2009, 08:53 AM
 
This is something I do all the time whenever I receive an AVI/MKV file ripped in the UK/EU format, for it is extremely annoying for me to listen to otherwise normal-sounding voices in cranked-up pitch. Of course I wouldn't dream of doing this to British-produced TV shows because those are shot in 25 FPS.

Anyway this is my method. Before I go into specifics, please understand that this method only works on Windows, for I have yet to discover a method for OS X. (Any Mac programmers out there want to make a quick buck, this is your chance.)

Programs you will need: Winnydows XviD4PSP, VirtualDub (comes packaged with XviD4PSP) and YAMB. All of these are freeware and work wonders.

On XviD4PSP: open the video file. Under Format choose MP4, and under Video Encoding, select anything that works for you. Note: We won't be encoding video so this step is really just to initiate the conversion rate process for audio output. Next go to menu bar, select Video>Interlace/Framerate. Choose Output framerate: 23.976 fps, and set framerate converter to AssumeFPS.
Now set your Audio Encoding to AAC-LC if your file has 5.1 channel AC3. Bitrate should be 224kbps or better. Be careful not to drop below that. Once this step is done, set your Video Encoding to Copy. Again, remember we won't be encoding any video for this step. Now finally click on Encode. After just a few minutes you will get an MP4 file with proper audio and the non-processed video.

Now on Virtualdub, open the AVI file. In the menu, select Video>Direct Stream Copy, (thus adjusting the framerate without reencoding!) and Video>Frame rate, select the radio button "Change to [ ] frames per second", key in 23.976 into the box. Then File>Save as... Remember, If this step takes you more than 10 minutes, you forgot to select Direct Stream Copy!

Next we will combine the video and audio. Fire up YAMB. Drag and drop the two files into the box to create/mux your final MP4 file, deleting the video and audio track as necessary.

Congratulations, you have just un-douchified a 25FPS AVI file. All under 15 minutes.
( Last edited by Bad Cyborg; Sep 11, 2009 at 09:05 AM. )
     
   
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