I've been doing multicam in Vegas for years but there's a required workflow. Multicam cuts need to be done before the color grading because multicam mode tosses all track and event fx. If you need a lut to see what you're doing, apply it as a media-level CGP. If you're applying luts at the media level as a chained FX, I think that will slow things down when you start using CGP. I think the grading panels get summed into a lut during processing but not with other chained FX.

After the multicam cuts are complete, I then expand back to the original camera tracks... usually one track per camera. That's where I do all the grading. If exposure is consistent throughout the shoot (ie, cameras white balanced and in full manual), I grade primary at the track level with only occasional CGP tweaks at the event level.

If I get footage from other cameramen without white balance and shot in auto exposure mode, it's allot more work. Because exposure and color balance changes with every camera move. And each time their camera moves or zooms, clip-cuts need to be individually graded at the event level. To ease doing this, I make heavy use of Grading Panel presets off of the FX chain. That way I can save a Grading Panel setup from one event and quickly apply it to a similar event shot at the same angle via the saved preset.

I do see some hesitation moving from one selected event to selecting another while remaining in the event-level grading panel. But it's never more than a few seconds, at most. Nowhere near 20. I do notice that as I'm moving through a 2 to 3 hours multicam shoot, it's more noticeable the longer I edit... if Live Save is enabled, it's allot worse. You might want to make sure Live Save is off. Another thing to consider is maybe temp storage might need a cleanup. Perhaps a Vegas reset on startup might help.

I wasn't even doing multicam. There were two short clips, one on track 1 and the other on track 2.

...A few minutes later. Now I'm not having any trouble. I restarted Vegas 21, not reset.

Now I know what caused the delays. I had been working with Smart Mask to create a Bezier Mask. Then I used Color Grading to adjust. Whoa!

Thanks Howard-Vigoriata for the benefit of your experience. However from my experiments it turns out the unusable color grading panel was down to the AUDIO. I wasn't expecting that!
BTW I regularly reboot the PC and restart Vegas. I dont use Live Save but often save incrementally.
I agree the best point in the workflow to color grade would be after the mulit-cam edit. If there's any error it'll show up worse at a camera change. So I went back to the point in the project after the edit and after expading back to multiple tracks. Totally unusable CGP.
Next I copied all the video clips from the timeline and pasted into a new instance of VP21. Now the CGP is virtually instant. Any clip can be selected and graded with no delay at all. Not the slightest hesitation jumping from one track to another back and forth over the hour with the panel open.
If I copy the audio tracks as well then the CPG is again unusable. So it's not down to corrupt project file. Back to the original.
I have two audio tracks one from one camera (24bit) as the main audio, and one from another as backup (16bit) which was muted. Both have some effects, compression and eq but it was not due to any of that. Only if I deleted both audio tracks would the CPG function. These tracks are the original .mp4 files from the cameras.
Next I rendered my audio track down to a single 16 bit .wav file and used it instead of the original. Now we have a working system with a pretty fast CGP. Even previewing in Good(Full) hence not using the proxys was possible.

I can see how the audio tracks might cause delays when scrubbing and scrolling through (which it didn't) but I cannot see why it would affect opening and using the colour grading panel. It does make sense to split the video and audio into separate streams but usually there is no need. The audio has to be extracted from a big .MP4, 20GB in my case, somehow. So when a video proxy is created maybe an audio proxy in the form of a separate .wav file should be createdas well.
Any ideas anyone?

@paul-marshall said: "These tracks are the original .mp4 files from the cameras.
Next I rendered my audio track down to a single 16 bit .wav file and used it instead of the original. Now we have a working system with a pretty fast CGP. Even previewing in Good(Full) hence not using the proxys was possible.

I can see how the audio tracks might cause delays when scrubbing and scrolling through (which it didn't) but I cannot see why it would affect opening and using the colour grading panel. It does make sense to split the video and audio into separate streams but usually there is no need. The audio has to be extracted from a big .MP4, 20GB in my case, somehow. So when a video proxy is created maybe an audio proxy in the form of a separate .wav file should be created as well.
Any ideas anyone?"

SWAG

If your audio tracks are literally the original camera files, then Vegas has to decode the video and audio to play the audio track. That would add significant load to the process along with the load of the CGP itself. Extracted .WAV files would be much less load. I suspect an audio track should be ...

...

...

...

...

... well, audio.

/SWAG

If your audio tracks are literally the original camera files, then Vegas has to decode the video and audio to play the audio track.

Of course - isnt that what it usually does? Anyway I dont see why that should delay the color grading panel from opening or make it unusable. Do you or anyone else demux into separate audio and video files? I suspect not.
Something is wrong and I dont know it is what but at least I have a work-around.

Why audio is causing issues with the color grading panel is strange. I'll keep an eye on it and if others can replicate would be good to get that confirmation here.

@paul-marshall

Let me ask a clarifying question. You do not have a separate audio track over and above the audio from your original camera audio?

@john_dennis
Not specifically. The audio track of one camera is ungrouped from it's corresponding video stream. And while the video stream is chopped up into many bits inter-cut with the other cameras, that sound track is pretty much un edited, its file 20GB of mp4 and lasts 45mins. I see now that a separate .wav audio track does make sense though it might be harder to keep in sync. Doing that does make the CGP work although I dont see why.

Displacing into a 20GB file to create an uninterrupted audio stream while displacing to other parts of the same file to play snippets of video from that and other files can be challenging.

I'd like to see a screenshot of your timeline. Or you could share your .veg file without any media.  I have lots of XAVC media I could use to replace your files.

@paul-marshall I find it surprising but maybe you're onto something. Didn't mention it earlier but as soon as I get my camera tracks into alignment, my next step is to do an Audio mix-down which I render to Sony Wave64 24-bit pcm format. After which I replace all the stems and audio tracks from the cameras with the mix-down. Only selecting the camera video tracks to create the multicam track. Thereafter, the audio mix-down is the only active audio track in later stages. Definitely no issue when I mute all the camera audio tracks. Mixdown, Multicam, and Grading stages look like this:

I can always go back to the audio-mix stage to tweak and regenerate the mix-down and the audio track update propagates.

This is a screenshot of the whole timeline after the multi-cam edit expanded to multiple tracks. I make extensive use of different window layouts on f keys.
It is a bit more complex than I said because two camera tracks have stills superimposed on them then I did an intermediate render to Pro-res LT. Those files were 80GB each, seemed a good idea at the time! Anyway that doesnt matter because it all worked great, It previews fine. It rendered out to HD and 4K with no issues and more or less finished. No crashes (except using Ttiler Pro 7 but thats another story) the only thing that was a problem was the CGP!
So I now realise that early in the workflow I should finalise the audio track and render that to pcm since it is kind of like the foundation for the whole thing. Still dont see what it's got to do with CGP though.
So when have I have time I'm going to redo it from scratch. Practise makes perfect they say!

The OP wasn't complaining about playback performance but rather

The color grading panel took 20 seconds to open and was unusable and another 20 secs to close

The order in which you do color correction doesn't matter if the tool is sluggish and unresponsive. If others are having the same problem we need to understand what triggers it so it can be fixed.

In either case:

My plan was to sync up my six video tracks then solo each one and do some color grading tweaks before I went to multi-cam edit mode.

Is not the recommended way to go about it. For performance reasons, it's always best to grade last.

This is a screenshot of the whole timeline after the multi-cam edit expanded to multiple tracks. I make extensive use of different window layouts on f keys.
It is a bit more complex than I said because two camera tracks have stills superimposed on them then I did an intermediate render to Pro-res LT. Those files were 80GB each, seemed a good idea at the time! Anyway that doesnt matter because it all worked great, It previews fine. It rendered out to HD and 4K with no issues and more or less finished. No crashes (except using Ttiler Pro 7 but thats another story) the only thing that was a problem was the CGP!
So I now realise that early in the workflow I should finalise the audio track and render that to pcm since it is kind of like the foundation for the whole thing. Still dont see what it's got to do with CGP though.
So when have I have time I'm going to redo it from scratch. Practise makes perfect they say!

 

The way I would go about this (to reduce clogged resources) is to render each of your six source videos with your CGP grading / corrections to lightweight digital intermediates first. Then open these in a fresh Vegas project, create the multicam timeline, and proceed as you have done. This eliminates two bottlenecks; 1) the burden of the source itself and 2) the color grading; the multicam project itself and your overlayed stills are in themselves resource hogs.

a "lightweight digital intermediate" might be MagicYUV, ProRes, XAVC-Intra, or even MPEG-2. Experiment to see which one gives the best performance on your timeline. Expect your intermediate files to be quite large.

Thanks guys for all your advice on multi-cam and color grading workflow. Not something I've ever done much of and now have a better idea what to do.

It does seem to be a good idea to mix audio down to a pcm track prior to multi-cam editing. The main advantage of keeping video & audio streams together is that they will always be in sync, or if one gets moved accidently is easy to restore. But that will be lost in multi-cam anyway.

@fr0sty What do you do for the audio tracks?