Please explain Rendering

I have not fully grasped if the process of rendering..
My understanding is that when you add a shot to the timeline or titles etc - it needs to render.
But my question is once it has finished rendering can I delete these files. I have a note about this been a good way to free up some space but I'm afraid to do this in case I mess up my edit.
Any comments or suggested tutorial would be appreciated.
K

If your project properties match your media you should not need to render the clips. You only need to render clips that have effects applied or titles or transitions or generators that aren't video. You don't have to render and most users I think switch off automatic background rendering. If something is rendered and you trash the render files, it will need to be rendered again. I use the word need loosely. In many instances, such as for transitions, there is no necessity to render for playback.

Also keep in mind that making ANY change to a title, transition or generator, even if you just move it, t will need to be re-rendered.

After an edit session or two, I go to File>Delete generated... and then I delete the UNUSED render files. This will reduce your Library size since those render files do take up space. I have on occasion deleted unused render files, only to go back into a project and find there are a bunch of things that need to be re-rendered for some reason.

But if a transition needed to be rendered and is now complete - will it have to re-render if I deleted the rendered files?

Yes. However need is relative. I need to render all transitions, but I never (almost never) do. You don't have to render. Rendering will speed up export to some extent, but of course you lose the time somewhere, and it can take a lot of resolution because the application renders to high data rate formats.

If this is an issue for you, you can turn off background rendering. Then, when you need to have an effect or transition rendered, you just select the relevant clips and press ctrl+R. That command renders only selected clips. Also, you can set your render quality to ProRes(LT). The default is regular ProRes 422. That will save a little space.

Hello iKitty
Perhaps a basic understanding of what rendering is will help. Whether you need to render or not is very dependent on you total system configuration, so sometimes it is or isn't beneficial/necessary.
Rendering is simply writing files to disk. Your computer is set-up by default to use background rendering when there is no other activity going on within the program (FCP/Motion). It renders to decrease the amount of processing that has to happen in real time to see something on screen without dropping frames. We may be talking about m(b)illions of lines of code being processed.
Things like effects, titles, audio effects, etc… are highly processor intensive. The type of codec and resolution also plays a big part in the necessity of rendering.
Simply playing back a rendered(written) file from a drive is much less processor intensive. The rendered file already contains all the results for the processes involved. The file is simply sent to RAM and played.
Now with modern CPUs and especially GPUs (video cards) processing video and audio can happen in real time, mostly, but with lots of caveats.
If your computer system barely meets minimum specs in RAM, CPU, and GPU, then allowing background rendering to happen will speed up your system once rendering is complete. If you have a top of the line system, then it most likely will not matter much.
This is the major reason I always recommend the best computer you can afford if you want to edit video.

Yes if you change anything within the clip, an effect, title, etc… then a new file is rendered/written in its place. Apply a moving title to a clip, let it render, then change the words and the orange bar will appear above the clip. It has to totally rewrite the entire clip file.
How long it will take to render is based on how fast your system is and since this is background rendering, how often you stop doing something for more than 5 seconds (by default). Ideally, with background rendering, performance is never negatively affected. YMMV
Also if you delete the render files from your drive, and have background rendering on, (preferences) then the app will simply recreate them, you gain nothing and make the computer work harder.
The only thing you will gain by removing rendered files is some extra space on the drive where you store them. As long as you have plenty of room on the drive, this won't matter.
You don't need to archive rendered files however, so delete them after completing the project.
In rare cases, if a rendered file becomes corrupted, then deleting them may be necessary to have the program work properly. Basic trouble shooting includes deleting render files.

So to use background rendering or not. If you have minimum specced computer, then I say definitely use it. If you are using a top of the line system or working in optimized or proxy media, then you may not need it at all.

Gone are the days of legacy FCP where with each change you had to wait for rendering to finish before moving on. Being able to continue editing is one of the things I love about FCPX.

Tom, AFAIK when exporting from FCPX, the project is totally re-rendered and does not use the stored rendered files, am I wrong about this? I have had issues when I attempt to export while background rendering is still working on the project. Seems to tie up additional resources, may be a bug where FCPX does not stop background rendering for export. When I export, it is usually to a different format.

Hope this helps, Greg

Depends what you export to. If you go to master file in ProRes, being rendered should see faster delivery times. Frankly I don't think it's worth it though. You lose the time somewhere. Also not wild about auto background rendering that is starting and stopping while you're working. It can't be a good idea to be building these files while continuously disrupting the process.

Great question, and one I never thought to ask, now that it has been asked, my understanding of rendering is nothing other than file caching to the hard drive instead of RAM.

If you make changes to the timeline, and the software tries to playback the new updated timeline, this will conflict with the cache file on the hard drive, and will need to be re-cached or re-saved to the hard drive before perfect playback will occur.

This is just my layman understanding of rendering in FCP X as it is not the same in motion 5, in motion 5, you do a RAM preview, which I assume from the letters R A M, this mean the RAM memory and not a fixed address on the hard drive, again I might be wrong!!!

Render files for playback are "flattened" files. Instead of FCPX having to composite multiple video and audio sources in real time, it writes one single flattened file (like flattening several Photoshop layers into one layer). One flat video file, one stereo audio file. When a change is made in the Timeline, that render file is no longer valid, is ignored, and a new render file would need to be written. It is only to make playback easier, that's it.

Thank you everyone for all your posts - I now have a much better understanding about rendering.
My conclusion for best workflow is to switch off bg rendering - especially during the titles making process etc so as not to over work computer - then once I'm done render all and upload...

iKitty2 wrote: - then once I'm done render all and upload...

Don't bother to render and export (Upload) in two separate steps at this point, just export, that step renders as part of the export process. As BenB points out, render is only to make timeline playback easier. Since you'd be done editing, just let FCPX finish your export with one step.

iKitty2 wrote: I have not fully grasped if the process of rendering....

Rendering is the process of converting a software model to a 2D or 3D image. When you invoke an effect that is a mathematical transformation that must be applied to every frame of the clip. Even though producing render files is a common practice, it is really unrelated to disks and caches since it could be entirely buffered in memory.

We often use the term loosely such as "render it out". However technically you render an *effect*, but but encode or export to a video stream or file. If the timeline is not rendered, then exporting may require rendering as one phase but they are distinct actions.

Premiere is very good at using the GPU for accelerated rendering of effects. This is indicated in the timeline by a yellow bar which means GPU rendered. Since FCP X doesn't use that color coding it is tempting to say it's more dependent on background rendering.

However if you just turn off background rendering in FCP X it does pretty well. Pre-render, it must use some approximation of the effect before actual rendering, maybe not that different than Premiere.

Even with Premiere CS6 when I used a lot of effects I'd eventually have to fully render it in the timeline to be sure of what I was seeing.

Despite the so-called "Mercury" GPU-accelerated rendering, the stabilizer effect in Premiere is excruciatingly slow. FCP X and most other 3rd party stabilizers are vastly faster yet still produce good quality. Ironically Adobe calls it "Warp" stabilizer -- it cannot possibly be referring to speed.

Re render file space, doing anything substantial in video editing takes lots of space. My suggestion is buy plenty of disk space and don't worry about meticulously deleting render files. That said, FCP Library Manager can safely clean up a lot of wasted disk space: www.arcticwhiteness.com/finalcutlibrarymanager/