Blackmagic Forum

I am stumped on this one and the only explanation I have left is software bug.

I simply cannot get the render cache to play smoothly.

I'm running Resolve Studio 15.0.0.086 on Windows 10 Pro (1803). I'm using cDNG from the Pocket stored on a dedicated Media drive with over 200 MB/s read speed and which plays back beautifully on its own.

I'm adding a Film Damage effect which understandably causes playback to stutter, given my GTX 960 video card. So, I render using DNxHD LB on 1/4 resolution stored on the same Media drive.

And it just will NOT play back smooth. It stutters every bit after render as it did before. I'm aware of the switch to turn Optimized Media on or off. It's on, but I assume not relevant for Render Cache. Is there such a switch specifically for the Render Cache?

Is the Render Cache not baking the effects into the new files? If not, the performance I'm seeing would be well explained. But then it begs the question, what is the purpose of the Render Cache? And how do we generate preview files with effects baked in?

Unless you have it set up so the node with the Film Damage effect isn't getting cached, what you're describing makes no sense. You should be able to render to full DNxHD HQ and play back without issue.

To avoid potential error, start over: remove any existing instances, add the fx to clips in the timeline (not in the color page), choose "user" for render cache, select the clips, right click and cache the output.

Have you tried setting setting render cache to user, proxy mode to off, and render color output (right click on the clip in the timeline) checked. Hope this helps

John Paines wrote:add the fx to clips in the timeline (not in the color page), choose "user" for render cache, select the clips, right click and cache the output.

Those are the conditions under which the original post was made and which simply do not allow a functioning Cache.

Tasio Liberakis wrote:Have you tried setting setting render cache to user, proxy mode to off, and render color output (right click on the clip in the timeline) checked.

Yes, that's how I did it in the original post.

I ran some tests on a second machine with a more powerful GTX 1070 using the same media and effects.

I found the more powerful GPU was able to play back the original media with Film Damage in real time without difficulty. I turned on the Render Cache for that clip, and it also played back without difficulty.

So I added a couple more effects, then a couple more, until I got to the point where real time playback wasn't possible using the original media. I again turned on the Render Cache for that clip but unlike with the single effect applied, this time it did not play back in real time.

So it looks like the Render Cache is NOT baking the effects into the new file. Which begs the question, how to we get smooth playback while editing with heavy effects?

I added Film Damage, Film Grain, Lens Flare, Light Rays, Color Compressor and Contrast Pop. Pre-caching, clip runs about 5fps. Cached to DNxHR HQX, clip plays without issue at 23.976.

If what you report is happening on two machines, the obvious suspicion is that you're doing something wrong.

You do see a blue line above the clip?

I do see the blue line. I don't know how it works for you and not me (on two separate machines).

Are you using the Windows version? Perhaps it's an OS specific issue?

Jim Simon wrote:I do see the blue line. I don't know how it works for you and not me (on two separate machines).

Are you using the Windows version? Perhaps it's an OS specific issue?

On what kind of a drive are the cache files located and is this drive shared by the source media or the project database location?

Cary Knoop wrote:

Jim Simon wrote:I do see the blue line. I don't know how it works for you and not me (on two separate machines).

Are you using the Windows version? Perhaps it's an OS specific issue?

On what kind of a drive are the cache files located and is this drive shared by the source media or the project database location?

This is a very important consideration - one should cache to a separate fast drive, NOT the same as the source drive. Reading the source while writing & again reading the cache - all on the same drive - might exceed the bandwidth of the source drive. I personally keep my source media on a 4x WD Black RAID 0 drive, but cached media go to a 1TB M.2 NVMe SSD drive.

Having said that, sometimes I also am under impression that not all effects have been baked into the cached media as playback from the M.2 drive is just a tad shy below the nominal fps speed of the project. I would appreciate it if someone from BMD authoritatively explained which caching scenario is supposed to bake all the color page nodes into the cached media. I *suppose* that when auto-caching, only the node(s) Resolve "feels" need caching will be baked in; however I tried the User mode and cached the output, reasoning this will bake in everything - and yet, with lots of nodes/effects - I still happen to not be able to play back full-speed from the cache.

What makes it even more "mysterious" to me is the fact that the cached media playback speed varies from one Resolve version to another. I had this problem in Beta 8, but in Beta 9 (and final DR 15 release) my cached media speed tends to keep the pace. What gives?

Piotr

Have you also tried specifically setting the node cache to On for those particular nodes? I find that Resolve's Auto setting sometimes doesn't turn a nodes cache to on.

StefColosi wrote:Have you also tried specifically setting the node cache to On for those particular nodes? I find that Resolve's Auto setting sometimes doesn't turn a nodes cache to on.

Yep - that's what I meant by trying to enforce baking-in everything (as opposed to what Resolve decides in Auto mode) by using the User mode, and switching all nodes' caching mode from Auto to On. The results (in terms of cache playback speed) didn't change, though - which is the very source of my confusion. Especially that - with exactly the same hardware - the cache playback speed changed from one Beta to another... Luckily enough, the compilation which now became the final Release 15, I have no problems whatsoever with my cached media playback... But it still bugs me, as it may change again with some next compilation (Release 16 Beta x).

I exchanged several PMs with Rohit Gupta from BMD Resolve Development team when Resolve 15 was still in Beta status, and maybe even the information I provided him with (regarding this issue) have somehow been used by developers - but it was never confirmed or explained why it happens (or not)...

Piotr

Cary Knoop wrote:On what kind of a drive are the cache files located and is this drive shared by the source media or the project database location?

That doesn't make a difference. Placing them on the media drive which is a 12 TB spinner with 200 MB/s read speeds, a 500 GB SSD with 450 GB/s read speeds, or the C: drive with 100 MB/s read speeds.

The issue persists regardless of codec, resolution, or location. The only constant I can find is if the GPU can't process the effects in real time. When that occurs, Render Cache won't play real time, thus suggesting that the effects aren't being baked in.

StefColosi wrote:Have you also tried specifically setting the node cache to On for those particular nodes?

I haven't made it to the Color page yet. I'm adding the effects to the clips directly on the Edit page.

Jim Simon wrote:I do see the blue line. I don't know how it works for you and not me (on two separate machines).

Are you using the Windows version? Perhaps it's an OS specific issue?

It's Windows, but the forbidden version (say what you like, but one advantage of using a defunct OS is, it doesn't change at the whim of Mother Microsoft).

It might be useful to a post a screen shot of your master preferences, to eliminate the potentially simple explanations.

John Paines wrote:It's Windows, but the forbidden version (say what you like, but one advantage of using a defunct OS is, it doesn't change at the whim of Mother Microsoft).

Resolve is state of the art software, I would strongly suggest you make sure your OS and drivers are up to date.

Release 15 requires the Windows 10 Creators Update.

I am using Windows 10 1803 on both machines.

When I add an effect that plays in real time, the Render Cache plays fine. It only stutters when I add effects that don't play in real time. I would consider this "proof" that effects are NOT being "baked in" to the Render Cache files.

The question: Is that by design, or a bug? If the former, how then do we get real time playback with heavy effects? If the latter, can we get this added as a priority fix to the schedule?

Steps to reproduce.

1. Test on Windows 10.
2. Use media that plays back fine in real time without effects.
3. Set Playback>Render Cache to User.
4. Add some effects to the clip on the Edit page.
5. Repeat Step 4 until real time playback is no longer possible.
6. Right click the clip, set Render Cache Fusion Output to On.
7. Allow the Render Cache to generate.
8. Play the clip.

Okay, it's obvious. You're rendering a fusion cache you don't have. Render color cache output or ofx.

Hi Jim,

Here : no issue.... check project setting or your HDD Drive cache
(Cliip Alexa ACES UHD @24 FPS on HD TL with set Render Cache Fusion Output to On. )

John Paines wrote:Render color cache output or ofx.

I'll take my dunce cap now.