Change cmx_3600 adapter to use transition duration frames (Issue #895)

[JoshBurnell]

The cmx_3600.py adapter appears to use a duration for Transitions that doesn't conform to the CMX 3600 spec.

According to this spec (Page 30), the duration is stored in a "RATE" field.

This guide makes it a little easier to read:

75 frame dissolve from reel 123 to reel 123B on video and A1:

Edit # Reel Name  Channel Trans      Dur      Source IN          Source OUT          Record IN         Record OUT
105 123    B     C        03:05:57:17 03:05:57:17 01:00:21:20 01:00:21:20
105 123B   B     D    075 03:15:33:09 03:15:35:24 01:00:21:20 01:00:24:05

However, the cmx_3600.py adapter appears to use the length of the previous clip:
https://github.com/PixarAnimationStudios/OpenTimelineIO/blob/84c8245c070b12d7e627c145435a5db9add0d2de/src/py-opentimelineio/opentimelineio/adapters/cmx_3600.py#L668

Test:

➜  OpenTimelineIO-JoshBurnell git:(issue-895) python3 tests/test_cmx_3600_adapter.py    
..............................
----------------------------------------------------------------------
Ran 30 tests in 0.285s

OK
➜  OpenTimelineIO-JoshBurnell git:(issue-895) python3 tests/test_cmx_3600_adapter.py EDLAdapterTest.test_transition_duration
.
----------------------------------------------------------------------
Ran 1 test in 0.092s

OK

[ssteinbach]

First of all, kudos for citing a document from 1988! Is there some way to get that as a citation/reference with a comment above the block where you set the transition duration?

[JoshBurnell]

lol If you look closely, I bet you can see the perforated edges of the dot matrix paper that that document was printed on. :-P

Great idea. I couldn't find a good reference link directly to something that said "Duration works like so..." but I'll add something.

[ssteinbach]

Do you know what the legal status of that document is? Is that something that we or ASWF could host? @jmertic do you know if there is a place for documents like that?

[jmertic]

Good question! Do you know the org that owns this spec? Or who used to :-)?

[mikekoetter]

TIL the CMX from cmx 3600 comes from CMX Editing Systems (a member of the Chyron group)
and the 3600 was a model of a "Highly popular online videotape editor" :)

[jminor]

SMPTE ST 258:2004 is the most official spec I know of for EDL
https://ieeexplore.ieee.org/document/7291839

The proper citation format is something like: "ST 258:2004 - SMPTE Standard - For Television — Transfer of Edit Decision Lists," in ST 258:2004 , vol., no., pp.1-37, 6 April 2004, doi: 10.5594/SMPTE.ST258.2004.

[jminor]

and there are mentions/links to two of the docs mentioned above here: https://opentimelineio.readthedocs.io/en/latest/tutorials/adapters.html

[ssteinbach]

Ok great, so in that case SMPTE is the organization that hosts the document and we should link to it with the citation that @jminor notes. Thanks everyone!

[jmertic]

Citation makes complete sense here :-)

One other thing to think about is if within the project there is an implementation of the spec; if so you likely would want to review the copyright/IP policy of the standards owner to ensure your use is allowed in that context. You probably are fine, but just mentioning it :-)

[JoshBurnell]

I updated the Citation per Josh's suggestion.

[ssteinbach]

Looks great -- one more last thing, if you accept the change, we can use assertIsInstance instead of assertTrue(isinstance(...))