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tiff frame sequences and frame rates

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Michael McCune
tiff frame sequences and frame rates
on Aug 30, 2019 at 5:46:37 pm


I have film scanned at 2K and then converted to a DPX frame sequence, which was then converted by Media Encoder to a tif sequence. In Resolve, after import, all seems to work as expected.

EXCEPT for a question regarding frame sequences and timeline frame rates. Here is the situation:
When tif sequence clips are imported into a 29.97 fps timeline, an alert dialog box may pop up saying the frame rate of the clip and the timeline differ and do I want to change the timeline frame rate (to 24 fps) to match the clip??? I understand that this frame rate mismatch alert is a feature of Resolve that is available when the first clip is dropped onto a new timeline and thereafter there is no frame rate mismatch alert even if there is a mismatch.

Dropping this same clip onto a 24 fps project timeline does not raise the alert dialog box.

Thus Resolve seems to recognize this clip as a (compatible) 24 fps frame sequence clip and not as a 29.97 fps clip.

Here is the question: If frame sequences have no inherent frame rate then what triggers this alert???

And, FWIW, exports from the Resolve deliver page also detect--and deal with explicitly--a 24 fps timeline clip when one tries to export it at 29.97 fps. It offers the option not simply of 29.97 fps but, "30 (3:2)." This is good.

So it seems that Resolve is handling this situation smoothly but also it seems to be recognizing these clips as 24 fps and performing 3:2 pull-up or pull-down as needed and on the fly for the timeline and for export. So the timeline export runs smoothly. (Again, that's good!).

But what is it in the tif frame sequence that seems to distinguish them as 24 fps or 29.97 fps???

Resolve seems to detect something in the tif frames. But what??? (I have even opened tif frames in a hex editor looking for a clue but didn't see anything obvious.)

Any thoughts would be welcome!

Thanks all. Mike

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Marc Wielage
Re: tiff frame sequences and frame rates
on Aug 31, 2019 at 1:48:30 am

If you check the TIFF with Clip Attributes, what does the Video Frame Rate read as?

It's possible there is embedded metadata in over which you have no control. Change them all to 29.97fps and see what happens.

Me personally, I would not drop a 24fps or a 23.976fps film scan into a 29.97 project without having a firm understanding of 2:3 pulldown and so on. Ideally, I'd convert everything to 29.97 prior to import so that I had more control over pulldown and potential interlace issues on cuts within the film.

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Michael McCune
Re: tiff frame sequences and frame rates
on Aug 31, 2019 at 4:53:23 am

Found it!!! This answers the question of how Resolve knows the frame rate of an imported frame sequence. Also shows other helpful info about the frame sequence, such as dates and times and pixel aspect ratio.

Here is the metadata from a frame, in this case using Media Encoder to create sequences with known frame rates. We encoded the original DPX into a 24.976 fps frame sequence, 24 fps and 29.97 fps.

Using a text editor (Notepad++) and a frame from the 23.976 fps encoding and then searching for '23.976,' we find:
Line 128: xmpDM:videoFrameRate="23.976024"

Also works for other example frames, such as 24 fps. Lines below are 123 to 133. (I expect that these xmp lines and data appear at the same line number location within every frame.)
And I also see the helpful info about pixel aspect ratio, here clearly indicating it is 1:1. (I had a problem recently in Resolve that seemed related to pixel aspect ratio but could only guess and deduce what the original pixel aspect ratio was. But here it is!!! Plain as day.
Note, from Wikipedia about xmp:
Extensible Metadata Platform - Wikipedia › wiki › Extensible_Metadata_Platform

The Extensible Metadata Platform (XMP) is an ISO standard, originally created by Adobe Systems Inc., for the creation, processing and interchange of standardized and custom metadata for digital documents and data sets. XMP standardizes a data model, a serialization format and core properties ... for embedding XMP information into popular image, video and document file ...


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Michael McCune
Re: tiff frame sequences and frame rates
on Aug 31, 2019 at 6:00:28 am

Complication: the xmp lines of info, described in the previous post, seem to be place ONLY in the first frame of the sequence. And the last frame of the sequence seems to terminate the frame and--and the frame sequence--with a series of "NUL/FS/NUL" triplets.

The frame sequence will nonetheless import into Resolve without the first or last frames but playback seems to show that the timing is off.

Also, Marc, you suggested to check the Edit page Clip Attributes. It does indeed show a value for fps BUT it appears to be only a drop down selection list with the field initially populated with the timeline fps.

So, as you say, Marc, it seems prudent to set up the frame sequence for the editor's timeline fps before importing it. That would seem to avoid some very tricky and hard to understand jitter issues, such as I found in playing with a frame sequence imported without an xmp head or a tail frame.

Any thoughts???
Thanks, Marc.

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