Rendering a video sequence with a Nodes-only scene strip fails with "No camera" error #38074

System Information
Windows 7 x64

Blender Version
Broken: 2.68.0 r58537, 2.69.0 r60995, 2.69 0074eac
Worked: Unknown

Short description of error
If a scene is created that does not contain a camera, but still has valid output (i.e., only a node network) and this scene is placed in a video sequence strip in another scene, attempting to render the video sequence fails with a "No camera" error, even though the video preview displays correctly.

Similar reports

#4463 (unclear)
http://www.blenderartist.org/forum/showthread.php?254572-VSE-render-says-no-camera (seems very close)

Exact steps for others to reproduce the error

Create the first scene, Main Scene. Ensure Sequencer is enabled in the scene properties.
Create the second scene, Scene 1. Ensure Compositing is enabled in the scene properties.
In Scene 1, go into the Nodes design surface. Ensure the Use Nodes check box is checked. Remove the default source, add another source (my use case is for Movie Clips, but I used an RGB source in the example as that also reproduces the issue), and wire the output to the Composite input.
In Main Scene, go into the Video Sequence editor. Add a Scene strip for Scene 1. Note that the video preview correctly renders Scene 1 (you may have to move off the current frame -- there are issues refreshing the current frame sometimes).
Attempt to render the video sequence by clicking the Animation button in the scene properties.

Recreated in attachment: Broken_Scene_Rendering.blend

Expected result: video sequence is rendered.
Actual result: video sequence immediately fails to render with error "No camera".

Note that this error is different than if there are no strips at all in the video sequence. In that case the error is "Cannot render, no camera".

Changed status to: 'Open'

Added subscriber: @jseigelis

Added subscriber: @KingAnderson34-4

Okay, I found the bug, but did you try adding in a camera in Scene 1 and then trying to render. I know the bug will still happen and should be fixed, but adding a camera in Scene 1 will get your job done.

Tried it again and this is still a bug. But, use my suggestion from my last comment.

Adding a camera does get rid of the error, but the output is wrong (the node network output no longer shows up in the video). I might be doing it wrong.

What do you mean by the node network output no longer shows up in the video?

I'm only using Scene 1 for Nodes, which has its own input and output. There are no 3D objects. When I place a camera in the 3D area, I assume it's looking at that stuff, not the output of Nodes, and so nothing shows up in Main Scene. Are you able to add a camera to the .blend file I attached so I can see how it's supposed to be done?

I think I've found the solution. To help you understand more, please take a look at these files I've assembled.

Broken_Scene_Compressed_fix_file_1.zip

my-system-info.txt

Screenshots:

Sorry I couldn't upload a longer video in the folder. The site has a 2 migabyte limit of uploading files. But anyway, hoped I helped. If not, just tell me what I did wrong. Thank you.

Huh... This time when I added a camera, the preview and output looks fine. I have no idea what I did wrong before.

Thank you very much for your help.

No problem, dude. Anytime. =)

Added subscriber: @ThomasDinges

So there is no bug here, can this be closed?

Using compositing alone can produce output, so IMO it doesn't make sense to require a camera in the scene. The error is clear, but if I don't need a camera because there's nothing to "look at" in 3D world (and the output I want is visible elsewhere), that's very confusing.

It might be simplest to let a camera be optional all the time. I would think that anyone doing 3D work should know enough to add a camera to view the scene. As long as there's no 3D output captured if there's no camera!

If the behaviour is changed to be consistent, then at least users will be able to figure out how to fix the problem on their own.

I guess it can probably be closed.

Added subscriber: @mont29

This issue was referenced by blender/blender-addons-contrib@61c9cacbd7

This issue was referenced by 61c9cacbd7

Changed status from 'Open' to: 'Resolved'

Closed by commit 61c9cacbd7.

Added subscriber: @brecht

I think this is a bug, fixed this now.

Thank you, much appreciated!

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Rendering a video sequence with a Nodes-only scene strip fails with "No camera" error #38074