How to export timestamps of multiple, synchronized clips in sequence?

[SteveSa]

Hello,

I'm a PP beginner and apparently do not fully understand how the sequence's frame rate, the synchronization feature and the Export option "Final Cut Pro-XML" work and relate to each other.

This is my use case:

I utilize PP to synchronize multiple clips before processing the clips with another tool in which I have to enter the clips' start timestamps to apply the synchronization there. I have to repeat this procedure for multiple batches of grouped clips and thus would like to use as much automation as possible, getting the results in a machine-readable file. In each batch of grouped clips there are clips with 30 FPS and clips with 29.97 FPS.

Currently, I use following workflow for each batch of clips:

1. Create a project
2. Add all clips to the sequence in different tracks of the sequence window
3. Select all clips and use context menu option "Synchronize".
4. Export the results in an XML file: "File->Export->Final Cut Pro-XML"
5. Parse the <start> tag for each clip in the exported XML file to determine the frame number in which the respective clip starts
6. Convert the frame number into a timestamp (relative to the beginning of the sequence) by dividing the frame number by the frame rate.

What I don't get:

What makes me curious is that the calculated timestamp sometimes deviates by a couple of seconds from the start timestamp of the respective clip displayed when hovering over it in the sequence window.

My first idea was that the different frame rates of the clips or alternatively the frame rate of the sequence need to be considered in step 6 instead of just assuming 30 FPS. I see that the XML file also contains tags for frame rate (<timebase>) and ntsc information (<ntsc>) but no matter which frame rate I assume, I fail to reproduce the start timestamp in the sequence window for at least some of the clips. Switching the sequence's frame rate between 30 and 29.97 seems to have an effect on the synchronization results as well as on the exported XML file but I still can't reproduce the start timestamp in the sequence window.

Is there something wrong with my workflow or does a more straight-forward workflow exist for my purpose? Do I misunderstand how frame rates and timestamps are used by PP?

[Kevin-Monahan]

Hi @SteveSa,

I read your note. You are having trouble synchronizing clips for preparation to use in another application. Is that right? Is this some kind of multicamera editing app? Sorry that I'm not fully understanding your workflow. Timecode can come in not only different frame rates, but also different flavors of timecode style. Drop frame and non-drop frame, which is for frame counting purposes. See if this article uncovers the anomaly you are facing: https://blog.frame.io/2017/07/17/timecode-and-frame-rates/

Let us know what happens after trying things from the article.

Thanks,
Kevin

[SteveSa]

Hi @Kevin-Monahan,

thanks for your reply!

Yes that is right. Actually, the other application allows coding the video data (i.e., adding annotations at specific timestamps for an evaluation of the recorded scene) for each batch of clips.

Thank you for the article regarding drop frame/non-drop frame. To double-check my understanding and the implications for my use case, I would like to know:

1. Given the information from the article, I would assume that drop frame is applied to the clips recorded with 29.97 and non-drop frame to the clips with 30 FPS. Is that correct or would I need to verify that somehow?
2. Could you help me understand how potential drop frames affect the counting? Let's assume we would like to know the timestamp for frame 18,000 for both types of clips: For the latter (30 FPS), frame 18,000 should be at 10:00.000. For the former (29.97 FPS), is it the same (but frames 1,800, 1,801, 3,600, 3,601, 5,400, 5,401, 7,200, 7,201, 9,000, 9,001, 10,800, 10,801, 12,600, 12,601, 14,400, 14,401, 16,200, 16,201 just not being accessible)? Or would the former clips be already 18 frames ahead, that is, at timestamp 10:00.600?
3. Is the frame counting solely dependent on the individual clip's frame rate/time code setting?
4. I see that in sequence settings, for the 29.97 FPS option I can choose between drop/non-drop frame rate. Which frame rate (30 vs. 29.97) and timecode style (drop vs. non-drop) should I use in the sequence settings if I have clips of both types in the sequence? How will these sequence properties affect frame counting?

Best, Steve

[Kevin-Monahan]

Hi @SteveSa,

Thanks for the question. Any clip can contain either drop frame or non-drop frame timecode. It depends on the camera person and how they recorded the original footage. You can verify the different timecodes by inspecting the numbers. If they contain a semi-colon, it is drop frame timecode. If it contains a colon, then it is non-drop frame. Most cameras shoot non-drop frame by default. Non-drop frame timecode is typically only used for broadcast TV.

This article contains info about the ramifications of timecode variants, and how to count the frames here: https://sonix.ai/resources/what-is-drop-frame-vs-non-drop-frame-timecode/

See if that answers your questions.

Thanks,
Kevin

[SteveSa]

Hi @Kevin-Monahan ,

thanks again for your reply. It has taken some time for me to test and verify what I am dealing with.

I do now know that the 29.97 FPS clips are non-drop frame. Note that within the sequence view of PP the colon/semi-colon display seems to depend on the sequence settings and not on the source files, that is why I asked the camera manufacturer to get the non-drop frame information.

Having that knowledge, consider questions 1 & 2 in my last post as no more relevant.

The questions not yet answered by the linked article are:

1. How do the sequence settings influence the results of the synchronization? According to the sequence settings and the NDF-knowledge, I have the choice to use 29.97 NDF or 30 for the sequence. Does this mean that when converting the frame number provided in the exported Final Cut Pro-XML file is a simple division of the frame number by the chosen sequence's frame rate? Or do I have to use the individual clip's frame rate for that calculation?
2. What are the advantages and disadvantages of using the further or the latter frame rate in the sequence settings for my purpose?
3. When playing back the synchronized, but not modified clips (with both frame rates of 29.97 and 30.0) in the other tool, would I need to slow down/speed up some of the clips to ensure the videos keep synchronized at all time? Is this what PP does when setting the appropriate frame rate in the sequence settings?

Best, Steve