Film at 24fps, telecine at 29,97, audio at 30. No sync.
by Alex Saggese
on
Oct 9, 2008 at 4:58:49 pm
Hello,
I have some footage that has been filmed in 35mm 24 fps and telecined into 29,97 NDF NTSC. The audio has been captured in 30fps NDF (real 30 fps). I've imported the flex files into Cinema tools and performed the reverse telecine to 24fps. I checked the converted files and they seem OK.
I get my audio as .WAV (BWF) sound clips. I imported it into FCP and tried to sync to my 24fps media. No matter what I try, the clips will loose sync after a minute. My audio is being pulled up. I also get green marks on the audio tracks of my 24 fps sequence telling me that I need sample rate conversion. If I change my audio speed to 99.9% it syncs, so I know it's being pulled up.
I think the audio is being imported at 29,97 instead of 30, and that is the source of my problems. I have not found a way to import it at 30.
I've tried the reverse telecine to 23,98 and it won't work either. I don't get the wrong sample rate line. In this case, the video is using the same pulldown as the telecine, but the audio is not beiong pulled down...
Is there a way to import my audio correctly (30fps)so that it syncs in 24 (or 23,98)?
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Steven Gonzales on Oct 10, 2008 at 2:00:47 am
On dual system film, sound and picture are in sync (assuming the devices are working properly) when captured.
Then, during telecine, the picture is slowed down by .1% to fit evenly onto 29.97 video.
So to sync at 29.97, you have to slow down the audio by .1% to sync.
If you also reverse telecine to 23.97, you have removed extra video frames, but you are still slowed down, and to sync audio you have to slow it down by .1%.
Your other choice is to conform your reverse telecine clips to 24 fps in Cinema Tools, and edit in a 24 fps timeline. If you do this, you have sped the film back up again. In this situation, you could sync the unchanged audio.
I think you have either reverse telecine clips at 23.97, or if you have reverse clips at 24, then you have placed them in a 23.97 timeline, and they remain slowed down.
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Alex Saggese on Oct 10, 2008 at 3:26:20 am
Hi Steven, Thank you for your reply.
I think maybe it didn't fully explain what's going on. I want to work in 24fps and use the audio without pulldown. Everything was captured properly. The audio synched at the telecine. What happens is:
If the reverse telecine is in 24fps, when I put my audio in the 24 fps timeline, it pulls up my audio. It even indicates it on my timeline saying that it's using a sample rate conversion to play. Well it shouldn't do anything, it should leave my audio unchanged so that it syncs.
If the reverse telecine is in 23,98, it doesn't do anything to my audio, but it should perform a pulldown.
My guess is that it's assuming my audio timecode is 29,97 NDF instead of 30 NDF, so it thinks it needs a pullup for 24 and no action for 23,98. I haven't managed to import the audio in 30 NDF, and I haven't seen any options for that. I want it to assume that my audio doesn't need change in a 24 fps timeline.
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Alex Saggese on Oct 10, 2008 at 1:44:06 pm
Reverse Telecine equals 24 fps, audio equals 48000Hz. I know that if the audio is played at the sample rate at which it was captured it will sync with my video at 24, but FCP won't let me play the audio at that rate. It performs a pullup. It tells me it's performing a pullup, it shows it right at the timeline.
I still think the problem is the timecode based, because if I convert the audio to aiff, for example, that has no timecode stamp, using the same sample rate, it works.
I think that the pullup happens because it assumes that the TC is 29,97, and to sync to 24, it needs a pullup.
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Alex Saggese on Oct 10, 2008 at 2:55:43 pm
Sequence is set to DV compressor Timebase 24 Audio Rate 48 kHz. Video plays fine. Audio captured from tape is also in sync. Imported audio does a sample rate conversion to speed up the audio when I place it on the timeline.
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by gary adcock on Oct 10, 2008 at 3:10:25 pm
[Alex Saggese]"ideo plays fine. Audio captured from tape is also in sync. Imported audio does a sample rate conversion to speed up the audio when I place it on the timeline. "
It is speeding up the audio to match the video - separate the audio from the video and it should play correctly.( just as you did with the Aiff file)
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Steven Gonzales on Oct 10, 2008 at 4:11:04 pm
Since it was the Cantar, I wonder if the setting was "C" Compensated (F) Faux mode. In this mode, the assumption is that the sound will be syncing with film converted to video rate.
The sound is recorded at 48048 samples per second, but it is tagged as 48000. This causes a .1% slowdown, perfect for syncing against film transfers at 29.97 or 23.97. However, if the sound was recorded this way, and then you have used reverse telecine to 24, the film is not slowed down.
However, the sound is slowed down due the recording mode used in the Cantar. Here's the rather confusing way this concept is explained from page 15 of the 2008 Oct. 02 manual:
"The 'C' mode is made for challenged post-machines. In a
file digitized at 48kHz, the Format stamp value indicates the
real number of samples per real-second, i.e. 48000, and
the Time stamp is the number of samples since midnight as
if the digitization was done at 48048!
Hence the 'F' name (for Fake or Faux) given by Fostex and
FCP to this mode. This is the mode selected by most US
productions. "
If this is the case, you should probably edit in a 23.976 sequence and conform your 24 reversed clips to that timebase with Cinema Tools, and all your film edit lists will still be fine.
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Alex Saggese on Oct 10, 2008 at 4:28:25 pm
Steven, thank you very much for all your help and effort. I checkd with the guy that captured the sound and he said that he never turnec the "C" on. He also said that if it was on it probrably wouldn't have synched on the telecine. So far it sounds like I've found a solution and I posted it.
Solution. by Alex Saggese on Oct 10, 2008 at 4:24:52 pm
I've figured it out. The problem was the timecode at which the audio was imported. BWF audio has no info whether it's 30 and 29,97, so FCP assumes the TC according to your sequence preset at launch. That means you have to change your sequence settings, quit FCP and restart. I read this at another forum, so I went to give it a try.
I used one setting that uses 30 fps (and not 29,97). Quit FCP and reentered. I created a new project to start from scratch and reimported all my audio and 24fps video. Created a 24fps sequence and put the video. This time it lets me sync without trying to change the speed. If I copy the audio from this project to the old one it doesn't perform the speed change either, so I guess everything is fine.
I also tryed redoing the whole process with sequences presets of 29,97, 24 and 23,98 and none of them worked. Always got the audio out of sync because FCP sped it up. I also tryed the sequence preset think without quitting FCP and that didn't work either, so I guess they were right when said that what counts is what's set at launch.
Hope that helps anyone that ever encounters the same problem, since the solution is not very straightforward...
Re: Solution. by Steven Gonzales on Oct 10, 2008 at 6:11:16 pm
Here's an old link from Andreas Kiel that says about the same thing you found:
"BWF Timestamp is readable since FCP 5.1.2 - but this doesn't mean that the timestamp is interpreted correctly, since it is interpreted based upon the setup FCP had at launch time."
Re: Solution. by Jeremy Garchow on Oct 10, 2008 at 8:08:30 pm
[Alex Saggese]"Hope that helps anyone that ever encounters the same problem, since the solution is not very straightforward...
"
No it is not. I have seen and heard about this problem when you receive and import audio recorded and intended for use in a PAL enivronment and your project is NTSC to start. It is an odd behavior for FCP as it seems to somehow tag the audio with an NTSC frame rate if that's what your start the program with and after you change the setting, the tag does not get changed and there's no way to change it unless you restart FCP and try again with the proper setup.
NO- not if you are converting 29.97 material- it should be 23.98 (23.976 for AE users) frames per second.
[Alex Saggese]"FCP won't let me play the audio at that rate. It performs a pullup. It tells me it's performing a pullup, it shows it right at the timeline. "
What? there is no such thing as "audio pullup"
First OFF- Audio files do not have frame rates, there are no frames in audio, audio is measured in feet and inches or minutes and seconds- there are not now nor have ever been frames in Audio.
[Alex Saggese]"I still think the problem is the timecode based, because if I convert the audio to aiff, for example, that has no timecode stamp, using the same sample rate, it works. "
Any issues would be in how you are handling the file- since your own test above explains my answer.
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows
Re: Film at 24fps, telecine at 29,97, audio at 30. No sync. by Alex Saggese on Oct 10, 2008 at 3:28:54 pm
I think I can work in either 24 or 23,98. The difference is that using 23,98 I can output directly to firewire, but I don't need that. With the reverse telecine at 24, my media goes back to its original speed and I shouldn't need to pulldown the audio.
Audio files don't have frame rates but are recorded with a timecode. The timecode is used to inform most systems about pulldown. For example. if you record DATs on location in 30 NDF and perform a telecine to 29,97 when you pulldown your DAT player, the TC rate will also be 29,97. That sounds uninportant in the computer world we live today, but if you're synching between your DAT player and your Beta recorder, it won't work if your DAT was not recorded at 30 NDF. There's no way it will sync, so the audio timecode is important.
BWF files have a starting timecode on them, and that timecode is important for post production. The starting timecode is recorded the following way: The number of samples since midnight, so if you use 29,97 or 30 you will get a different starting timecode and the timecode will have a different rate during play. I can't have that, so I need it to have the right timecode.
If audio is sped by .1% some people call it a pullup, so that's why I used the term. When your final product is going to be film cut from negative, but all your audio is mixed at 29,97 using video tapes, you need to perform an audio "pullup" to sync back to your film. In reality you're just removing the pulldown.
On my telecine tapes, I only get 2 channels, but on my BWF files, I get 4. I need them all, so I can't use the audio from the tapes only.
I know the problem is how I'm handling the audio files, and I think it's got something to do with the way I import them in FCP. In other systems that cut film, it really matters for your sync if you import your audio in 29,97 or 30. I haven't seen that option in FCP and for some reason it's trying to change the speed of my audio when it doesn't need to, so I'm assuming that's the reason.
It's my first time cutting film in FCP, I've always used Avid. I'm a fan of FCP and would like to give it a try.
