Exporting videos with an Alpha Background

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Jeffrey Howard

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Exporting videos with an Alpha Background

PostWed Aug 30, 2017 2:59 am

I have spent the past night trying to figure this out, and am ready to pull my hair out, so if anyone has any insight on this it would be greatly appreciated!

I am using Resolve 14 Beta (just downloaded it, was using 12.5ish Free). I am trying to export a video with a transparent background that I can use as a transition on my Twitch stream. I have found a video on YouTube showing how to do it on Adobe After Effects, but no luck with Resolve (just search "How to Make Video Transitions with Transparency in OBS " on YouTube, if it helps).

The whole video is 5 seconds of some PNG files coming off screen, joining together on screen to block the whole screen, then they all go back off screen. I just need the background to be transparent when I export, but can't figure out how to do that. All of my PNG files do have transparent backgrounds, so I have that figured out.

I completely understand if this is just not possible with Resolve, I just figured I would pick the minds of the forum before completely giving up.
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Uli Plank

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Re: Exporting videos with an Alpha Background

PostWed Aug 30, 2017 5:25 am

It works fine for me in DR 14 beta, but in ProRes 4444, uncompressed RGBA or image sequences only.

Which format are you trying? DNxHR/HD seems not ready yet.
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostWed Aug 30, 2017 7:41 am

Jeffrey, this is indeed easily possible if your codec deals with alpha channel. Best example : ProRes 4444.
Also have a look on youtube and/or in the manual to see how to add an alpha output in the node tree.
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Jeffrey Howard

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Re: Exporting videos with an Alpha Background

PostWed Aug 30, 2017 3:06 pm

Thank you both for your replies!

I'm not sure if I am overlooking it or its just not available in the free version, but I dont see prores 4444... Is it under QuickTime? I exported as uncompressed argh but vlc and media player classic dont seem to have thr natural codec to play it, do you have any suggestions on any codec packs I should download to play it?

Alpha output in the node! I bet thats my problem. I'll try to search when I get off work and post what I find out. Thank you!
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostWed Aug 30, 2017 4:20 pm

ProRes is not available under Windows in Resolve, only in Fusion 9, that may be the problem (but I don't remember if you wrote about your system).
Otherwise, codecs with "a" (argb for ex.) mean they deal with the alpha channel. Therefore you could try animation or uncompressed argb
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Uli Plank

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 2:31 am

On the PC you don't have much of an option yet for more than 8 bit, other than image sequences.
"Animation" or uncompressed should work, but with huge files and limited bit depth.

Let's hope that BM soon fixes the DNxHD/HR output.
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Jeffrey Howard

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 3:12 am

Yes, I am using Windows.

So I played around with it a bit more and realized what I needed to do to create an alpha background; I had to right click the node tree, click "add alpha output", then link the nodes, then make sure to click the individual files and Export Alpha options when rendering. BUT I am now having a problem with most programs using the exports. VLC and OBS (my streaming program) seems to hate all the exports I've tried (Grass Valley, Uncompressed ARGB/BGRA, I even went back to 12.5 and tried DNxHD), even Quicktime sometimes won't play them. I don't see a Quicktime animation option, where would that be at? I understand this isn't a forum for VLC or OBS, but does anyone have any suggestions on why they wouldn't play the video files?
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Peter Cave

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 4:44 am

On Mac OSX the DNxHD 1080p codec exports ok with alpha channels. You do need to add an alpha output on the Color Page or there will be no alpha (or full raster alpha) in the output file.
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Uli Plank

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 6:35 am

Thanks, Peter,
need to try that, DNxHR didn't work for me, even if it offers an alpha channel.
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 8:13 am

Peter Cave wrote:On Mac OSX the DNxHD 1080p codec exports ok with alpha channels. You do need to add an alpha output on the Color Page or there will be no alpha (or full raster alpha) in the output file.
Just for me to know because I understand you're writing it to make it clear about the codec, but how come anyone on OSX could prefer it to ProRes 4444 ?
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Uli Plank

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 9:32 am

Teamwork, maybe?
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Peter Cave

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 11:37 am

Sam Steti wrote:
Peter Cave wrote:On Mac OSX the DNxHD 1080p codec exports ok with alpha channels. You do need to add an alpha output on the Color Page or there will be no alpha (or full raster alpha) in the output file.
Just for me to know because I understand you're writing it to make it clear about the codec, but how come anyone on OSX could prefer it to ProRes 4444 ?


DNxHD is the native Avid codec. Using Avid round trip grading workflows with Resolve, DNxHD is an easier format to use and does not have some of the interchange issues that ProRes can exhibit. I prefer ProRes if NOT working with Avid systems. Some of my clients only work with Avid codecs and will not accept ProRes.
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostThu Aug 31, 2017 12:11 pm

Yep of course, Avid codecs are crossplatorm, Uli also rang the bell about collaborations made on exports.
It's my fault, I haven't seen a macuser on Avid for a while (I'm talking about Media Composer), most of them are on FCPX, Premiere, FCP7 and Resolve... Itend to behave as if it was the whole world :)
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Jeffrey Howard

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Re: Exporting videos with an Alpha Background

PostTue Sep 05, 2017 11:32 am

Just as an update: No luck using resolve; I ended up trying some other video programs and it works pretty easily using Hitfilm Express, using some basic settings.
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chrisbrearley

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 12:10 pm

Is this nonsense getting sorted in 15? Just spent the last hour trying to get an alpha out of Resolve on Windows to no avail. The only codec options with alpha seem to be DNxHR which don't seem to work. I can see video layer 1 underneath layer 2 which is the layer I want to export in both the edit and colour page with with my external matte plugged into the alpha output in the node graph. Set to render individual clips with Export Alpha ticked. Do I get an alpha? No. I seem to remember having more success under 12.5. Is this a codec issue? Why do TIFF, DPX and EXR not have an Export Alpha tickbox option?
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Andrew Kolakowski

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 12:39 pm

What if you don't render individual clips? This may be your problem.
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 1:25 pm

BMD's Peter (or some else ?) had finally answered this in the meantime in another thread : try rendering a single clip instead of individual ones from your same TL (put and i and o for the test purpose if needed)
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chrisbrearley

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 1:31 pm

Nope, no difference. Here's Jeff.

resolveALpha.png
resolveALpha.png (763.62 KiB) Viewed 2759 times


No difference with an external matte added, you can still see the video layer 1 underneath. It shouldn't need one anyway as it is carried in the source clip I just tried it as it wasn't working without. As far as I can tell my render settings are correct. Turning video layer 1 off when rendering for a timeline render also does not work.

Also not the way that I have to stack and offset my parallel node stack even though I am working on UDH monitor... 150% GUI scaling anyone??
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chrisbrearley

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 2:44 pm

Exporting ProRes 4444 from a Mac works so the problem seems to be with the DNxHR implementation. This leads me to my earlier point, why is there no alpha option with TIFF, DPX or EXR?
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 4:31 pm

I just played around with this and am also stumped. On Windows (no Prores 4444). From what I understand, DNxHR 444 supports alpha so I wonder what the deal is. Would be nice if someone from BMD chimed in...

Cheers
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Jean Claude

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 5:56 pm

Here no problem.

A TIFF => Fusion TAB => Luma Keyer (without adding Alpha option ... with even simpler option :) )
Color TAB => add Alpha Output
Delivery => Quicktime => DnxHD 444

Reimport delivery:
Clip Attribute => Alpha Mode Premultiplied

Result
Result.jpg
Result.jpg (71.91 KiB) Viewed 2747 times
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chrisbrearley

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 6:04 pm

I've just tried rendering a Quicktime DNxHR 444 12bit as opposed to an MXF and Resolve sees the alpha when reimporting. However After Effects does not see the alpha. Who's to blame I don't know but I'm no better off. Need TIFF, DPX etc....
Last edited by chrisbrearley on Wed May 16, 2018 10:34 am, edited 1 time in total.
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostTue May 15, 2018 8:21 pm

I gave this a shot and it sort of works. I tried adding a blur to a text object and the premultiplication looks a bit odd when I bring the media back into Resolve.

I also tried another test where I put a circular window over my footage (in a node on the color page) and added an alpha output channel - connected the windowed node to the alpha output channel and then generated the output media on the delivery page - that also works but there is something off regarding the edge of the softened circle.

So - I'm not quite there - missing some key knowledge I guess...

The output file is an DNxHR 444 10-bit but I tried with DNxHD 444 and DNxHR 444 12-bit and got the same odd edge behavior.

I am not a smart man, miss jenny...
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostWed May 16, 2018 5:09 pm

Is it possible that DNxXX 444 expects alpha as premultiplied white whereas Resolve expects premultiplied black (or vise-versa)?

I ask because Media Composer offers to treat alpha in one of three ways (straight, premultiplied white and premultiplied black) because Avid historically treats premultiplied different than Adobe (IIRC). Given that Resolve does not offer this option, is it possible that this is causing problems with DNxXX 444 and the alpha generated from within Resolve.

Bear in mind that I don't know what I'm talking about, lol.
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Jean Claude

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Re: Exporting videos with an Alpha Background

PostWed May 16, 2018 5:23 pm

Steve Alexander wrote:Is it possible that DNxXX 444 expects alpha as premultiplied white whereas Resolve expects premultiplied black (or vise-versa)?

I ask because Media Composer offers to treat alpha in one of three ways (straight, premultiplied white and premultiplied black) because Avid historically treats premultiplied different than Adobe (IIRC). Given that Resolve does not offer this option, is it possible that this is causing problems with DNxXX 444 and the alpha generated from within Resolve.

Bear in mind that I don't know what I'm talking about, lol.


Hi Steve,

You should try in MC (we can reverse in MC: OK :) )
Fusion Tab => invert Luma
invert.jpg
invert.jpg (151 KiB) Viewed 2690 times


result
Result.jpg
Result.jpg (112.04 KiB) Viewed 2690 times
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostWed May 16, 2018 8:00 pm

Thanks Jean Claude -

I did pretty much that and found that it worked well unless I introduced a softened edge to the hole - then the resulting alpha didn't look right. Not sure what's going on there.

Also - I couldn't bring this back into MC to see the alpha so I've definitely done something wrong...
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Uli Plank

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Re: Exporting videos with an Alpha Background

PostWed May 16, 2018 10:09 pm

You know that alpha only gets rendered if you set Deliver to individual clips, do you?
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 1:01 am

Then I have it backwards - I thought it was the other way around - single clip renders alpha... I'll keep playing with this... that could be my whole problem. If I ever figure this out I'll do a tutorial covering the workflow.
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Sam Steti

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PostThu May 17, 2018 7:59 am

That's what I told you 2 days ago ;)
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 2:21 pm

Not really, Sam - This is what you said:

"BMD's Peter (or some else ?) had finally answered this in the meantime in another thread : try rendering a single clip instead of individual ones from your same TL (put and i and o for the test purpose if needed)"

This is incorrect - in order to make use of Alpha for DNxHR 444 10-bit and 12-bit you must select the 'Individual clips' mode. I'm not sure if you posted the reverse of what you meant but I was following your advice (which didn't work for me) and now I see that if I select individual clips that I get an addition option to 'Export Alpha' for DNxHR 444 10-bit and 12-bit. The 'Export Alpha' option is not available when selecting the 'Single clip' option.

I have now successfully exported a short timeline with a power-window applied in the CC panel with an alpha output and that seems to work just fine (bringing it back into Resolve - the alpha is perfect). I haven't tried bringing it into Media Composer yet - but I will.

I also tried (separately) to use a mask in Fusion to see if I could also delivery a DNxHR with alpha but I don't seem to be able to get that working correctly.

Tiny steps, Ellie...
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 3:55 pm

Tried using the file in Media Composer and received a core consistency check failure. Nothing is easy - lol.
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Sam Steti

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 4:17 pm

Yep sorry Steve, I didn't post the reverse of what I meant on puprose, I admit I just made a mistake :oops:
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Steve Alexander

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 4:21 pm

No problem, Sam - I didn't think there was any malevolence involved - lol
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chrisbrearley

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Re: Exporting videos with an Alpha Background

PostThu May 17, 2018 9:19 pm

Yes it seems Resolve can export an alpha channel from Windows using DNxHR MOVs but only Resolve can see the alpha. So pretty useless. We had to resort to exporting the project to an old iMac and rendering some prores at about 2fps.

Peter, is this getting sorted??
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Jean Claude

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Re: Exporting videos with an Alpha Background

PostFri May 18, 2018 5:29 pm

Sorry,

For the moment it is still a V15.BETA: if it is possible it is to call in VFX connnect or in Standalone Fusion Studio (on PC) and RENDER in PRORES4444. AVID immediately recognizes ALPHA :)

In Davinci Resole : ALPHA is 'Strainght' :oops:

Import_After_FU_PRORES_4444.jpg
Import_After_FU_PRORES_4444.jpg (22.75 KiB) Viewed 2513 times
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Bruce Allen

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Re: Exporting videos with an Alpha Background

PostMon Jun 04, 2018 3:54 pm

Hey, so from this thread it seems I can't export an .EXR or a 16bit LZW .TIFF with alpha?

My only option is DNxHR or uncompressed DPX? And I can't choose between premult & straight?

That's sad - I was hoping for a nice clean workflow doing some work that we traditionally do in Nuke in Resolve / Fusion then piping work back and forth with the Nuke artists.

Feature request for Resolve 16, I guess!

Of course the ideal would be where you could export and input multiple named mattes as channels in the EXR. And have those come in as separate layers.

That way you could pass separate, named matte channels for separate elements etc between artists, roto, 3d tracking, etc as we often do in Nuke.

Bruce Allen
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Bruce Allen

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Re: Exporting videos with an Alpha Background

PostMon Jun 04, 2018 4:10 pm

Hmm, just tried DNxHR 444 12bit with Export Alpha checked and it doesn't show up in After Effects...

Yes, with all of the power Resolve has with Fusion etc it's going to be used a heck of a lot as the center of a VFX workflow, so I hope they get this all sorted out!

Bruce Allen
Senior Theatrical Designer & TD - mOcean

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