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Sync drift - am I doomed?
Old 22nd November 2009
  #1
Gear Maniac
 

Sync drift - am I doomed?

I'm using Pro Tools LE 8.0.
As I feared, our unorganized post workflow has turned into a big sync problem. I'm hoping someone here can help me figure out what's going on - even if it means we're screwed and I'm going to have to manually re-sync everything.

Actually, I think I might have just found the main issue. It looks like the first video file that the editor gave me was 29.97fps. The TC burn, and the settings he uses to edit are 24fps. So, it looks like he should have given me a 24fps DV encode - not a 29.97fps DV encode. I didn't notice this originally, because of my lack of video knowledge. Before I started this project I asked here at Gearslutz "what is a recommended codec for video in post audio?" - and determined for my situation that DV would be best. At that time, I thought all DV NTSC was the same frame rate - so I didn't check the video file that the editor gave me.

I put a lot of time into a rough mix, knowing that a couple changes in the video might happen. They did. I just got a new file from the editor and started manually (no EDL or DV Toolkit here) conforming a few chunks of audio where they needed to be moved. That's when I noticed that even when I synced up a chunk at the beginning, it would be out of sync after a minute or so. So I started comparing the two video files I have gotten from the editor and sure enough, the recent one is DV at 24fps while the original one is 29.97fps.

After about 4 minutes it ends up about .25 of a second off.

My guess is that I've got a whole lot of work ahead of me. It seems like I've read of some way to change a PT project from one frame rate to another. But that might require DV toolkit or something.

Any info is very appreciated. I'm going to go cry myself to sleep now...
Old 22nd November 2009
  #2
Lives for gear
 

Whatever the reason do no accept deliveries from the editing room at different frame rates unless requested by you.

I'm Swedish and do not have a lot of experience with the specifics of videotransfers in the US standards (we have 24 & 25 fps here).

But mixing video framrates is generally a big no-no for good workflow.

OTOH It should be possible to just pull the project to the proper framerate (or convert the video) so it syncs up again. Just hold on and I bet you'll get some good advice.
Old 22nd November 2009
  #3
ruy
Gear Maniac
 
ruy's Avatar
are you working with omf's?
Old 22nd November 2009
  #4
there are a lot of issues that could be happening here.

assuming the editor cut the piece at 24 FPS - then the picture is at FILM SPEED. If the editor cut the picture at 23.976 the picture is running at VIDEO SPEED. If you imported OMF's and the Audio lined up with the picture ( forgetting frame counters at this point ) then you are probably ok and the project is at VIDEO speed. If the OMF and picture did not line up there is a good possibility that you are running at video speed and the picture is film speed. Check your frame rates make sure its not 23.976 and 29.97 ( both are video speed). An easy way to check this is to check the full second frames 00:00:01:00 or 00:11:15:00 if you are running at 29.97 and the picture is 23.976 then the FULL second frames will line up , but the frames within the seconds will not. If this is happening, breath a sigh of relief and reset your frame rate to 23.976. If the edit actually is in fact running 24 FPS at FILM SPEED. You do in fact have a sync issue.

Bottom line, I think you are running video speed and the picture is running film speed if long pieces of audio are starting in sync and falling out. BUt there can be other issues. Is the piece cut in Final cut? if so there are a lot of gotchas' on the FCP side as well. FCP accepts various frame rates, audio sample rates and formats. And here's the kicker... FCP will "adjust" these various files to work properly, but it OMFs will get all squirrily and materials with the wrong sample rate brought in to Protools from FCP could be misaligned or may fall out of sync.

First and foremost, verify the frame rate and speed of the picture cut with the editor.

cheers
geo

The first question to ask when dealing which projects: is the picture frame rate in sync with 48kHz. If so there will be no need to do a sample rate conversion or digitize via analog sources to change the sample rate of the incoming audio signal. Otherwise check out these various project paths....

1. Feature film – double system at 24fps and 48kHz audio recording for 24fps postproduction.
2. Film-based television providing sync dailies on DigiBeta (23.976 and 48kHz) for 23.976
postproduction.
3. Film or HD Production at 23.976 with single or double system audio recording for 23.976
postproduction.
4. Feature film and film-based television production at 24fps with hard disk recording at 48.048kHz for 23.976 postproduction.


1. Feature Film Double System

Most, if not all, feature film production intended for theatrical shoots film at 24fps while recording audio digitally at 48kHz. the film is now running at 23.976fps during the telecine process in order to create a known 2:3 pulldown cadence to the 29.97fps video rate. Once digitized into a 24p project, the frames are “stamped” as 24fps in order to play back in sync with audio captured directly via AES/EBU or Broadcast WAV files recorded at 48kHz. Because the audio was captured digitally – either synced to work clock or imported as 48kHz – it expects to be in sync with the picture as it was originally captured – 24fps. The native sample rate of a 24p project is 48kHz and all other rates are resolved to that during capture. When playing back at 48kHz, the audio plays back .1% faster creating a true 24fps playback from 23.976 sync sources. When capturing digitally at 48kHz, no samples are converted. It is a digital clone.

2. Film-Based Television with Sync Dailies
The transfer facility has already resolved the original shooting rate of 24fps to 23.976 and has sample-rate-converted the digital audio sources to be in sync in the digital source tapes. the audio must be sample rate converted when going from 24fps to 23.976 on the video. The path looks like this: Picture: 24 -> 23.976 to 29.97 video creating 2:3 pulldown Audio: 48kHz -> 47.952 slow down (.1%) sample corrected -> 48kHz to 29.97 video. If the editors are cutting in a 30i project (29.97 NTSC video), the audio sample rate is unchanged when capturing – it is a digital clone.

If it’s decided that postproduction will work in a 24p project, the digitized samples are slowed to bring everything back to a true 24fps = 48kHz environment.
In this case, the postproduction should be done in a 23.976 project type, since it assumes that the 48kHz audio sample rate is in sync with picture playing back at 23.976fps from the DigiBeta captured sources. It has the same result than that of a film-to-tape transfer to tape. But since there is no need to speed up to true 24fps in this project, audio samples remain untouched at 48Khz throughout the postproduction process, through the audio mix and back to the NTSC broadcast master. Using this project type for this workflow will only go through one sample rate conversion during the film to tape transfer.

3. Film or HD Production at 23.976
shooting rate is 23.976fps because of the audio consideration when down converting to NTSC. No one wanted to deal with a sample rate conversion in the audio when working in a fully digital environment. In a double system environment, the DAT or hard disc recorder records at 48kHz. So shooting at 23.976fps eliminates the need to do a sample rate conversion. The resulting NTSC down convert is now the same as in the previous example where 23.976 video with 2:3 pulldown is in a Digital tape with sync 48kHz audio.
If working double system, the DAT or BWF files from the hard disk recorder, the 48kHz recording will come straight in with no sample rate conversion or speed change to sync with the 23.976 picture.

4. Feature Film with 48.048kHz Audio Recording
audio workflow at 23.976 with the film running at 24fps. This workflow is only for picture capture frame rate of true 24fps and a NTSC postproduction workflow. DAT, and more common to this workflow, hard disk recorders, can record at 48.048 kHz – which is really just 48kHz with a .1% speed up as part of the capture.

Film/24p Settings
editing systems with 23.976 project types support a 48.048kHz BWF import workflow. If no sample rate conversion is chosen, the imported files are stamped as 48kHz, thus slowing them down by .1%; the same amount that the film is slowed down during the film to tape transfer. This way no sample rate conversion is performed, and a digital audio pipeline is maintained for the postproduction process.

Capture, Edit, Digital Cut
Capture: The project type determines the native capture rate of the project, either 23.976 or 24p. It also determines the native audio sample rate of that project that will not have a sample rate conversion or analog process involved when capturing, playing, or digital cut.

Edit: In the Film/24p settings you will see the “Edit Play Rate” as either 23.976 or 24. This control sets the play rate of the timeline. It does not affect any of the digital cut output settings. This control lets you set a default state of frame rate for outputs that are made directly to tape, such as a crash record.

Digital Cut: Here you can output the timeline as 23.976, 24, or 29.97. The important thing to remember is that this is the playback speed of the Avid timeline, not the source tape destination. The NTSC frame rate of 29.97 cannot be changed. What is changing is the frame rate of the picture within the NTSC signal.

1. 23.976. This creates a continuous 2:3 cadence from beginning to end of a sequence and is the expected frame rate of a broadcast NTSC master from 24 frame sources.

2. 24: This is used for feature film production to create a true “film projected” speed from an Avid timeline on NTSC video. It is also the output type to use when using picture reference in a Digidesign Pro Tools system using OMF media from a 24p project type. Note that this is not a continuous 2:3 cadence. Adjustments are made over 1000 frames with the pulldown cadence. No frames are dropped, just the field ordering with the 2:3 cadence.

3. 29.97: Timeline will play back 25% faster to create a 1:1 film frame to video frame relationship. This can be considered a 2:2:2:2 pulldown cadence. This
output is useful for animation workflow or low cost kinescope transfers where a 2:3 pulldown cannot be properly handled


So find out exactly what path the production team used and find out how i was edited and finally what speed/frame rate they want you to work in and to deliver to.
Old 22nd November 2009
  #5
Here for the gear
 

Ok I have a ? for you georgia. It seems to be on this topic. I have a friend who just got a new panasonic hvx500. It has bcn timcode in so we tried to sync with it but we noticed that the cameras 24fps is really 23.98. I use a 702T and BoomRecorder but neither of them have 23.98. Would 23.976 be the best to work with 23.98? What do I need to do to get correct sync in post?
Old 22nd November 2009
  #6
Quote:
Originally Posted by sysyphus300021 View Post
Ok I have a ? for you georgia. It seems to be on this topic. I have a friend who just got a new panasonic hvx500. It has bcn timcode in so we tried to sync with it but we noticed that the cameras 24fps is really 23.98. I use a 702T and BoomRecorder but neither of them have 23.98. Would 23.976 be the best to work with 23.98? What do I need to do to get correct sync in post?
24 is 24 FILM SPEED
23.98 is 23.976. VIDEO SPEED it's just another way to say it. ( round up 23.976 = 23.98 )
do not confuse 24 FPS with 23.98 FPS or 23.976 FPS

as to correct sync... There is frame rate and there is speed ( film speed or video speed ) I have a couple of panasonic HVX200A's they can run both 24 and 23.98. ie: both film speed and video speed. I'm sure the HVX500 can do both as well. If you set the camera up for 23.98 and 48Khz run at video speed for 1080p, 1080i or 720p and run the recorder at 48khz, 23.98 all will be well. if you want to shoot at 24 film speed, you can record on the boomrecorder at 48 with a pulldown during the post process.
My cameras also do 480 30p which is kinda cool. I can do squeeze mode, run Standard Def, 480 but end up with a video cut in 16:9 progressive 48 Khz, video speed. Handy for multimedia and web delivery. My HD delivery from the HVX200A is 1080i or 720p 48Khz. I don't use the 24 frame mode, but I have a DP friend who rented a full set of 35mm lenses, shot in 24 frame mode, "film look" mode on the 200A and the picture looked amazing for a $5k camera. Mostly I shoot multimedia, web delivery, broadcast demos, docs, and reality on these cameras and deliver at SD 480 or HD 720p.


Convert 60i to 24P
Use this option for standard interlaced NTSC shot at 1/60th sec shutter speed, where you wish to edit at 24P for the purpose of transfer to film or to author a 24P DVD. If this option is selected, all film effects (widescreen, grain, red boost) will be disabled. These effects can be added after editing.

Convert 3:2 Pulldown to 24P
Use this option for NTSC which was shot in 24P normal mode with a standard 3:2 pulldown, or with video that originated on 24 frames/sec film, where you wish to edit at 24P for the purpose of transfer to film or to author a 24P DVD. If this option is selected, all film effects (widescreen, grain, red boost) will be disabled. These effects can be added after editing.

Convert 2:3:3:2 pulldown to 24P
Use this option for NTSC video that was shot in 24P with a 2:3:3:2 pulldown, or 24P-NTSC archival material created with a 2:3:3:2 pulldown. Convert 2:3:3:2 Pulldown to 24P is the only option that works without recompression of the video data.


Output 23.976 (23.98 )
Use this option to output 23.976 frames/sec Quicktime with 48000 Hz audio, instead of 24.000 frames/sec Quicktime and 48048 Audio. This option works best with editing programs that can set the timeline to exactly 23.976 frames/sec. If this option is not used, then the Quicktime's playback rate is 24.000 fps and the audio playback rate is set to 48048 Hz to keep perfect sync, and the 24.000 frames/sec timeline must be set up for 48048 Hz audio.


hope this helps.....

cheers
geo
Old 22nd November 2009
  #7
Lives for gear
 

To be clear--the 702T DOES have 23.976, but they call it 23.98 to save a digit in the display. The sync will be fine w/ the camera--esp if you can get the TC out f the camera and have the 702T input it.

Philip Perkins
Old 22nd November 2009
  #8
Quote:
Originally Posted by philper View Post
To be clear--the 702T DOES have 23.976, but they call it 23.98 to save a digit in the display. The sync will be fine w/ the camera--esp if you can get the TC out f the camera and have the 702T input it.

Philip Perkins
thanks Philip... I went down a video rathole there...
Old 22nd November 2009
  #9
Gear Maniac
 

Thanks. I'm trying to wrap my head around all this.
First of all, there wasn't much usable production sound and I didn't get OMFs. I worked from a temp stereo mix. I don't have DV Toolkit, so I can't import OMF anyway and I don't really see any frame rate stuff on my end.

I checked the video files by opening them with QT and getting info. Also, I just put them in Final Cut and checked the properties - the original says 29.97 and the new one says 24fps.

Considering that the original video file I worked from is 29.97, it's starting to look like there are too many variables for me to use any kind of 'automatic' fix.

I'll re-read some of these posts and see it I can make any more sense of the situation.

Really, I still don't understand why the real-time of my audio wouldn't simply match any frame rate - even if he gave me a file that was 3.14159fps. Does it mean that PT is playing one (or both) of these files back at the wrong speed?
Old 22nd November 2009
  #10
Lives for gear
 
TVPostSound's Avatar
Quote:
They did. I just got a new file from the editor and started manually (no EDL or DV Toolkit here) conforming a few chunks of audio where they needed to be moved. That's when I noticed that even when I synced up a chunk at the beginning, it would be out of sync after a minute or so. So I started comparing the two video files I have gotten from the editor and sure enough, the recent one is DV at 24fps while the original one is 29.97fps.
You're overthinking this. Who says the video editor just edited chunks??
What if he was frame f%$ing?

The question is, does it "drift", or does it just go out of sync all of a sudden??

I just recently got a DVCProHD at 24 from an FCP editor, it was actually 23.98.
When the session was getting too fat to roll HD, I converted it to a SD DV, it made it 29.97, the video length did not change.
Old 22nd November 2009
  #11
Gear Maniac
 

Quote:
Originally Posted by TVPostSound View Post
You're overthinking this. Who says the video editor just edited chunks??
What if he was frame f%$ing?

The question is, does it "drift", or does it just go out of sync all of a sudden??
Well, there have been some issues where he sent video for color correction. When he got it back he said he had to manually adjust frames here and there. So that is one of the variables I mentioned that might make it difficult to 'automatically' fix.

And I'm pretty sure that the sync is steadily drifting. Whether it's because of f%$ed frames here and there or not, I don't know how to find out.
Old 22nd November 2009
  #12
Gear Maniac
 

I'm starting to feel like this is too much of a mess for any of you to want to deal with. But I'll try anyway:

Below is the latest email I got from the editor. Any idea how I should answer his questions?

Note: when he says everything has been in sync - that's not my opinion. The newer files that I have gotten from him (where he had conformed my rough mix) were out of sync when I inspected them on my systems. Again, more variables that I can't pin down. A DVD I got from him is strangely out of sync on my home DVD player (differently than when I check it on my computer! - and all other DVDs play synced fine in both). The new DV encode I got seems out of sync in different sections.

Quote:
I'm not sure what is going on at your end. The new reference video that I gave you is in sync on my end, I'm looking at it now.

Worst case scenario would be to keep working without worrying about the changes to the sequence and just make those areas clean cuts and when you send the final edit over I can worry about moving the scenes then. Any holes that are left at that point you can address as a separate project.

That would be the safety net plan since everything has been working with sync up to this point.

About frame rate issues I apologize about the first DV encode being 29.97 - I don't have that file anymore so I can't check on it, but it came from me so I must have done that.
Is your audio sequence set to 24fps or 29.97?
All versions of our timelines and movies are at 24fps and that is also in the timecode on the original reference video.

The Good News is that everything you have been doing so far is working good when you send it back to me, so it stands to reason that if you keep on doing what you're doing that it will sync up well when you send it next time.

If you need that new reference vid as 29.97 i can make that for you np.
Personally, I think I'd rather get a new 24fps DV file of the final locked cut and re-sync everything (nearly starting over) - rather than to go back and work off the old video (possibly with scattered frame problems) and letting him try to fix it.
Old 22nd November 2009
  #13
Gear Maniac
 

One question that might help me understand a little more:

Hypothetically, let's say the editor gives me a 29.97fps DV file. I import that video into PT and work on it. Then, the editor gives me a 24fps DV file of the same cut. If I import that 24fps video, replacing the 29.97fps track in PT - would my audio be out of sync?
Old 22nd November 2009
  #14
Lives for gear
 
Henchman's Avatar
do not work in 24fps.
Old 22nd November 2009
  #15
Gear Maniac
 

Quote:
Originally Posted by Henchman View Post
do not work in 24fps.
Even if that's what the footage was shot in?
Old 22nd November 2009
  #16
Lives for gear
 
Henchman's Avatar
Yes.
How do you expect to lock up with blackburst and do the audio transfer/
It seems pretty obvious to me, that your video guy is pretty clueless.
Old 22nd November 2009
  #17
Gear Maniac
 

This is all new to us. First film, DIY. To be honest, the crew pretty much consists of the director, the editor (who shot most of it) and myself (all post audio engineering).

Considering this, the production value is actually quite high... except for the technical problems that I'm trying now to fix.

So, how would you recommend proceeding at this point?
Old 22nd November 2009
  #18
Gear Maniac
 

BTW, our highest hopes would be to be considered for something like SXSW. A mid-sized festival somewhere perhaps.
Old 22nd November 2009
  #19
Lives for gear
 
JSt0rm's Avatar
if your video is 29.97 and the editor worked at 24p then you need a .01% pull down on the audio attached to the 24p session. This will put it inline with your 29.97 session. Soundhack can do this also a option in protools.
Old 22nd November 2009
  #20
Gear Maniac
 

Just to be clear:

The footage was shot 24fps. The editor is editing in 24fps. He accidentally sent me a 29.97fps DV file that I did a rough mix for. Now there have been a few changes to the cut and I need to import a new video file.

What format of video file should I ask the editor for?

Do I need to do some kind of pull down conversion? And if so, can PT do it without DV Toolkit?

Will anything need to be done when I have a mix for the editor to conform back to his video in Final Cut?
Old 22nd November 2009
  #21
Lives for gear
 
JSt0rm's Avatar
if he gave you 29.97 before then all your audio is at that rate.

24p is .01% higher

cheapest easiest way is to
1. use sound hack on all the header information. Change that number from 48000 to either 48,048 OR 47,952 (pull up or pull down)

THEN

2.import into session without sample rate converting it back to 48k This will force it to play at that slower or faster rate in your session and be in sync.

Now I would recommend taking a 2-track stem to try this on until you know the exact settings. You wont see any drift on a little bit of audio and hacking header information on 1000 little audio files is NOT fun
Old 22nd November 2009
  #22
Gear Maniac
 

Quote:
Originally Posted by JSt0rm View Post
cheapest easiest way is to
1. use sound hack on all the header information. Change that number from 48000 to either 48,048 OR 47,952 (pull up or pull down)

THEN

2.import into session without sample rate converting it back to 48k This will force it to play at that slower or faster rate in your session and be in sync.

Now I would recommend taking a 2-track stem to try this on until you know the exact settings. You wont see any drift on a little bit of audio and hacking header information on 1000 little audio files is NOT fun
Thank you.
However, I don't know enough to understand the details about this process.
At soundhack.com, there are a bunch of freeware apps that I don't know the first thing about. So I don't know how to "use sound hack on all the header information". I just don't know what that means.

Then, "import into session without sample rate converting it" sounds like I should do this:
Duplicate my current PT Project
Apply this "sound hack" to the files in the audio folder (?)
Create a new PT Project
Import the new 24fps video
Import the tracks from the duplicated/soundhacked project

That's my best guess of what you're saying.

This conflicts with Henchman's suggestion to not work in 24fps.
Old 22nd November 2009
  #23
Lives for gear
 
JSt0rm's Avatar
Ill go backwards

Import the tracks into protools WITHOUT sample rate conversion. I think the command is ADD

header information is text information at the head of an audio file that says what sample rate and bit depth the file is. When you hack this information you are tricking your computer to think it is slower or fast.

http://music.ucsd.edu/~tre/soft//SH896.zip

^that is sound hack

command+o opens a file

command+h or k will open the header info (its been a while don't remember exactly)

punch in your numbers then command+s to save.

Like I said do this to a 2-trk FIRST so you know exactly what to do. Check your drift and you will see that it will either get twice as bad or get in sync. If it does anythign else your problems are worst.
Old 22nd November 2009
  #24
Lives for gear
 
JSt0rm's Avatar
sorry this stuff is pretty crazy. I'm hazed on it. I think you might want to sample rate convert the audio back to 48khz after the slowdown as it will still play it back at that slower/faster rate. Make sure to try both as my memory is fuzzy.
Old 22nd November 2009
  #25
Lives for gear
 
JSt0rm's Avatar
Quote:
Originally Posted by bradhebert View Post
Thank you.
This conflicts with Henchman's suggestion to not work in 24fps.
ohh I'm not conflicting with henchman You shouldn't work at that rate (or if you do it is a long conversation before hand) but if they are unable to output you a 29.97 picture that syncs to your audio then this is your option.
Old 22nd November 2009
  #26
Gear Maniac
 

Well, they did output a 29.97 from it and that started the problem.

They could give me a 29.97 version of the new cut if that would make this fix easier.
Old 22nd November 2009
  #27
Lives for gear
 
JSt0rm's Avatar
have them give you a 29.97 file and if its in sync continue to work. Then hand them back the file and run

or do all that crap i just told you 1 time on the stems instead of 1000times on omf dx
Old 22nd November 2009
  #28
Gear Maniac
 

Ok, I'm going to try a 29.97 version of the new cut.

If anyone sees a problem with this, please let me know.
Old 23rd November 2009
  #29
Gear Head
 

I'm working in a little post house that is doing a lot of publicity projects. Here, this is christmas all year long regarding frame rate and sync workflow ( since most projects are driven at lightspeed by producers that mainly eat amphetamine for breakfeast ). To avoid many complications we are working only at 29.97 all the time even if we have to convert the video files and ignore the burnt in tc.

Since we do this most sync issues disapeared from our day to day work.

just my 2 cents
Old 23rd November 2009
  #30
Gear Maniac
 

Thanks everybody. Once again, this forum has proved invaluable.

I converted the latest cut, which was given to me at 24fps, to 29.97 like the previous cut I was working from. No drift now!

I'm guessing that when I give the editor my mixdown, it will sync up in his Final Cut - even if his project is 24fps? I believe it worked last time (without us realizing I was working on a 29.97 file).

I hope one day to really understand why frame rate changes my sync in Pro Tools, but I can mix to a different frame rate than the editor and it will be in sync when I give them my mix. Basically, why does the frame rate change the duration of the movie in Pro Tools? It seems the video would be the same length no matter what frame rate.

Well, at least it seems to be working. This has been such a learning experience.
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