add rendering notes

[meshula]

This PR adds notes on rendering since rendering behavior is unclear from the specification itself.

[codecov-commenter]

Codecov Report

Merging #1679 (86b0074) into main (cbef407) will decrease coverage by 6.16%. Report is 81 commits behind head on main. The diff coverage is n/a.

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[darbyjohnston]

What would also be really useful is the equivalent of the "project settings" in Final Cut Pro for establishing the output resolution, audio format, etc: https://support.apple.com/guide/final-cut-pro/final-cut-pro-project-settings-ver1b946a4ff/10.7/mac/13.5

Currently in tlRender I make a guess at the settings by using the video and audio from the first clip in the timeline. This works mostly OK but fails in some situations and also requires opening the media.

[reinecke]

I spun the project settings suggestion @darbyjohnston made into #1683 - I know it'd been talked about before but we'd failed to capture it as an issue. Thanks for highlighting it again!

[meshula]

@reinecke @darbyjohnston Does my edit on compositing ring true?

[darbyjohnston]

Looks good to me, thanks. For transparent clips that allow the background to show through, we assume the background color is black?

[meshula]

@darbyjohnston yes, I added a bit about zero values, and 100% values for alpha. Note that I specified zero, not black, because if we say "black" then it invites discussion about black levels and what we expect to happen for non-zero blacks. I also said 100% so that no one wonders if we mean "1", "1.0", or "255" or ...

[darbyjohnston]

Thanks, I think the note about "zero" is good so we don't get into color issues as you mentioned. Why the 100% alpha? For viewers it is nice to preserve the alpha channels for checking renders, though that could also be achieved by viewing the individual elements instead of the final composite.

[reinecke]

This update looks really good to me. On the background color, I think 100% opaque zero color values is a good baseline to match most NLEs. That said, if an application wants to allow people to override that behavior, there’s nothing stopping them.

[meshula]

If someone wants to go ahead and approve, we can merge.

[darbyjohnston]

It looks like the DCO check is failing...

[meshula]

right, if we accept changes in the online form, as we I did, the dco is not attached. heavy sigh.

[meshula]

Does anyone know a trick for repairing that? If not, I'm inclined to just merge, as there are not enough hours in the day to recreate a PR and go through the whole rigamarole again

[reinecke]

I forced DCO pass and merged - thanks for updating the docs @meshula