Resolve 17.1 - Deliver Tab - Render Failure (not always)

Resolve 17.1 - Deliver Tab - Render Failure (only in specific projects)
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Using Davinci Resolve 17.1, I have some existing video projects that fail to render. The problem symptoms are that, after the render job "starts" it never shows any progress. Additionally, the render job refuses to actually cancel after hitting the "stop" button. The UI also becomes generally unresponsive, in that it is not possible to return to the edit tab (for example), and attempting to quit Resolve produces a dialog box that asks if the render job should actually be cancelled before quitting.
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In task manager afterward, I can see after trying to quit Davinci Resolve once the render job failure problem occurs, that there are about half a dozen hidden dpdecoder.exe tasks running (with associated conhost.exe tasks with them). Those hidden tasks require several minutes to shutdown before Davinci Resolve can be restarted.
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note - My Windows computer has reasonable resources: Intel 10900K, 32 GB RAM, nVidia 2070 Super GPU, Crucial P5 NVME SSD storage. Normally rendering is quite fast.

I have traced the source of the - render failure - problem I have just discovered to - built in fusion titles - used within a video project. I tracked down this problem by creating a small test video project, and then adding features one at a time until the problem appeared.
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Curiously, once the - render failure - problem occurs, it appears that simply removing the offending fusion titles does not repair the rendering problem within that project. (very curious)
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Most specifically, it seems that if a - fusion title - is placed a track and given a length of more than a couple minutes, video delivery rendering fails, and the only way to get out of the problem is to quite Davinci Resolve. What makes matters worse is that I have discovered that even deleting the titles entirely doesn't repair the problem.
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One of the other symptoms of this problem is that, when a render job starts normally, one can see in Task Manager that all the systems CPU cores suddenly soar to about 98% usage, demonstrating that the computer is using all its resources to render the video. When the problem described in this post appears, after clicking the render job button, the CPU utilization never begins, but Davinci Resolve, seems mostly - frozen - with the only way to get out of the "crash" is to force quite the application.
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I have tested this problem with small test video projects that can be reproduced within a few minutes. I can make test projects available to blackmagic support if requested.

Are the Fusion titles in question native, or third-party?

If native, which ones?

Does it only occur after changing the length of the title?

The same happens to me. I have a title about halfway through the project. Resolve 17.1 renders UP UNTIL the beginning of the first title (Long Title Lower Third, specifically, in my case). My project hangs in rendering at 45%--stopping right at the beginning of the title.

My suggestion would be to render out the Fusion compositions by themselves as individual files, then bring them back into Resolve so they're all ready to go.

I think the new "Render in Place" function can also do this, but make sure you're at the correct resolution when you do so.

Fusion is a bit of a beast in terms of CPU, RAM, and GPU requirements.

Are the Fusion titles in question native, or third-party?

If native, which ones?

Does it only occur after changing the length of the title?

This serious problem occurs with any native (Resolve 17) Fusion Title, it doesn't matter which one.
( Note however, that the problem does not appear specific to Resolve 17 native Fusion Titles. )
This problem may imply some kind of bug (limitation) in Fusion related to the Fusion 'Keyframe Stretcher' node that is (oddly) failing after a specific length. In other words, it seems possible there might a problem with the "math"/"algorithm" inside that Fusion node.
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To reproduce this problem ...
Create a project, insert any native Fusion Title (you don't even need a video track).
Then click Ctrl-D and change the length of the title to six (6) minutes, and save the project.
Go to the deliver tab, and setup an render (the settings don't matter).
Then start the render.
The render will appear to begin, but then nothing actually happens. Upon clicking the [ stop ] button, the button does NOT respond.
In fact, Resolve is essentially all but frozen.
The only way out is to close down the entire application, to which Resolve displays a response, but still the only way out is that Resolve has to be shutdown.

My suggestion would be to render out the Fusion compositions by themselves as individual files, then bring them back into Resolve so they're all ready to go.

That sort of response gives the appearance of the admission that a software problem/bug exists, for which the only current workaround, is a clumsy kludge.

Fusion is a bit of a beast in terms of CPU, RAM, and GPU requirements.

People are using computers with plenty of "horsepower", resources, and so on.
This problem is not in any way related to computing power, this problem is a Davinci Resolve (apparently fusion component), software problem.

My suggestion would be to render out the Fusion compositions by themselves as individual files, then bring them back into Resolve so they're all ready to go.

Your wise suggestion seems like the most practical workaround for the short term.
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Our shop already does this after creating complex graphics package elements, which get rendered out with alpha channel, with little or no compression.
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People should note though, that for best results, it is not only important to have all the attributes matching the primary project, it is important to render with as little compression as possible. A side effect of this is graphics elements that use significant disc space (as though that matters much these days [LOL]).
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This same principle also applies to our shop's - sound design - elements, which are created with other audio production/synthesis tools (render in highest possible audio resolution in a lossless format).

I tried a variant of your test. I added a Fusion title to a 7 minute timeline I had available for testing and dragged it out to fill that.

Render got off just fine, and Stop also worked just fine.

This is in Studio 17.1 for Windows using a meager 4GB GTX 970 .

I tried a variant of your test. I added a Fusion title to a 7 minute timeline I had available for testing and dragged it out to fill that.

Render got off just fine, and Stop also worked just fine.

This is in Studio 17.1 for Windows using a meager 4GB GTX 970 .

To clarify, the fusion title itself needs to be long, in your case seven (7) minutes should be enough.
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Also, as I have noted (several times), this problem doesn't have anything to do with computing resources.
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This problem, is clearly a problem with Fusion Titles, and creating fusion titles that exceed (not quite fixed length) a short on screen duration.
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This problem is easily replicated with such Fusion Titles as:
- "Clean and Simple Heading Lower Third", and
- "Horizontal Line Reveal"
When the problem occurs it is quite apparent, and quite alarming since it requires a shutdown of the application.
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Notably, as well, as this discussion thread demonstrates, other Resolved users have observed this problem. Just because you haven't created the content needed to reproduce the problem, doesn't mean the problem doesn't exist.
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The purpose of posting about this problem, is to make both BlackMagic Design aware of it, and to make other Resolve users aware of it, so that the problem can be researched and resolved, hopefully by both various Resolve users experiencing the problem, and by BlackMagic Design.
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Reporting about this sort of problem requires valuable time, and it isn't done idly.
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Just because you haven't created the content needed to reproduce the problem, doesn't mean the problem doesn't exist.

Agreed. But if we can't find easily duplicatable steps, it could mean it will be more difficult for BMD to track it down.

I added the Horizontal Line Reveal to a 13 minute timeline and dragged it out for the duration. I started the export and let it run about half way, then stopped it.

Everything worked. I was unable to duplicate the issue.