Export with alpha

Hello experts,

When I export with alpha it doesn't seem to work properly and doesn't include the alpha channel.

I'm trying to export a short clip as MP4 (H.265), I've checked the option for the alpha channel in render settings, but when I try to use the file afterwards (like overlay it on something else in a new project), the alpha channel has not worked.

I've done this dozens of time before, I've got several MP4 (H.265) files on my desktop right now, that I've masked > alpha'd > exported with DaVinci Resolve, so I know this should work.

I haven't used DaVinci Resolve in a few months so I must have forgotten something, another option I need to change somewhere.

Does anyone have any ideas what I'm forgetting?

I can't speak as to the exporting of H.265 with Alpha channels, but I will point out that if you want to export with an Alpha channel it implies that you intend to bring that exported clip back into Resolve (or some other video processing product) in order to composite it with something. H.265 is a lossy codec and perhaps not the best choice for this.

When I do alpha exports I do so using MFX OP1A / DNxHR codec. This uses more disk space but has more fidelity, and the alpha channel definitely does work with it.

I can't speak as to the exporting of H.265 with Alpha channels, but I will point out that if you want to export with an Alpha channel it implies that you intend to bring that exported clip back into Resolve (or some other video processing product) in order to composite it with something. H.265 is a lossy codec and perhaps not the best choice for this.

When I do alpha exports I do so using MFX OP1A / DNxHR codec. This uses more disk space but has more fidelity, and the alpha channel definitely does work with it.

Thanks for the reply. I tried that file type and the alpha worked properly.
It's massive overkill for my needs though, I'm just making some low resolution junk for my friends. The file type you suggested came out 300x larger than the file size I'm expecting for my 3 second clip.

I really just need to know which setting it is that I've forgotten, that's stopping H.265's alpha channel working here, as I know that it should work.

Thank you for your reply though

I really just need to know which setting it is that I've forgotten, that's stopping H.265's alpha channel working here, as I know that it should work.

Thank you for your reply though

Mp4 h.265 is a little 'quirky' - after importing, you need to select the clip attributes and select 'Premultiplied' in the 'Alpha Mode' for the alpha to show.
Quicktime h.265 and DNxHR selects that attribute automatically when importing and shows the alpha.

Is that the step you 'forgot' - clip attributes?

I really just need to know which setting it is that I've forgotten, that's stopping H.265's alpha channel working here, as I know that it should work.

Thank you for your reply though

Mp4 h.265 is a little 'quirky' - after importing, you need to select the clip attributes and select 'Premultiplied' in the 'Alpha Mode' for the alpha to show.
Quicktime h.265 and DNxHR selects that attribute automatically when importing and shows the alpha.

Is that the step you 'forgot' - clip attributes?

That's strange, I have multiple clips that I made before (about 6 months ago), all Mp4 h.265, and they all just work, I don't need to change the attributes to make the alpha work. I just drop them in and they have transparency.

I can't make any new ones that work though. The moment I hit 'Render' the 'Export Alpha' checkbox deselects.

This is what the files show, the ones I made previously with DaVinci Resolve, they all say that they include the alpha in the codecs and they all work properly. Any new h.265 ones I make do not include that alpha part and the transparency doesn't work.

I really just need to know which setting it is that I've forgotten, that's stopping H.265's alpha channel working here, as I know that it should work.

Thank you for your reply though

Mp4 h.265 is a little 'quirky' - after importing, you need to select the clip attributes and select 'Premultiplied' in the 'Alpha Mode' for the alpha to show.
Quicktime h.265 and DNxHR selects that attribute automatically when importing and shows the alpha.

Is that the step you 'forgot' - clip attributes?

Quicktime h.265 doesn't work for me either. It does exactly the same as Mp4, the alpha channel does not get included in the exported file.

I think h.265 export is bugged in the current version of Resolve, I'd be interested to know if anyone can successfully export h.265 on a silicon Mac and preserve the alpha, as for me it doesn't work at all anymore.

But I've found a workaround.

If I export as AppleProRes 4444 (resulting in a massive file), I can then select the exported file on my desktop, 'Encode Selected Video Files', choose HEVC, which gives the option to 'Preserve Transparency'. Mac will then convert it for you and the alpha works just like it used to in Resolve, no need to mess around with clip attributes, no blocky mess and it's a nice small file that's only 1% the size of ProRes.

This is what the files show, the ones I made previously with DaVinci Resolve, they all say that they include the alpha in the codecs and they all work properly. Any new h.265 ones I make do not include that alpha part and the transparency doesn't work.

Is it possible you're using a different encoder? On my system not all of the encoders support alpha channels...

H.265-Encoders.jpg (48.68 KiB) Viewed 3356 times

Have you added the Alpha output on the color page?

Did you use "Main" for the profile? It seems that H.265 in Main10 on the Mac doesn't offer alpha.

I think h.265 export is bugged in the current version of Resolve, I'd be interested to know if anyone can successfully export h.265 on a silicon Mac and preserve the alpha, as for me it doesn't work at all anymore.

I'm on Windows and don't know about Mac - different beast.
Can't imagine it's bugged.

Sean, Robert and Uli offered some good comments.

As I wrote, it's limited to the plain Main profile, but it works for me on a Mac with Apple silicon.
You have to tell DR to use alpha in the Clip Attributes.

This is what the files show, the ones I made previously with DaVinci Resolve, they all say that they include the alpha in the codecs and they all work properly. Any new h.265 ones I make do not include that alpha part and the transparency doesn't work.

Is it possible you're using a different encoder? On my system not all of the encoders support alpha channels...

The attachment H.265-Encoders.jpg is no longer available

Hi Sean,

I don't even have an encoder option when I go to export my clip. Mine looks like this.

Have you added the Alpha output on the color page?

Hi Robert,

Yes I have. I add an alpha output on the color page, then I drag the line to link up to the blue dot. Then I do m magic mask and the alpha shows properly when I play back on the timeline.

It just doesn't render the alpha channel in my final when I export my video. It still 'blacks-out' the area I want to remove from the clip, it just doesn't include the transparency in the video so I cannot use it as an overlay.

I've exported dozens of clips this way and it's always worked before, it just doesn't work anymore.

Did you use "Main" for the profile? It seems that H.265 in Main10 on the Mac doesn't offer alpha.

I used 'Main' and always have done.
If you select Main10, the 'export alpha' checkbox disappears so you have to use 'Main'.

As I wrote, it's limited to the plain Main profile, but it works for me on a Mac with Apple silicon.
You have to tell DR to use alpha in the Clip Attributes.

I tried that when you mentioned it before, that creates a horrible blocky outline which makes it unusable.

It used to work perfectly well, without needing to go into 'clip attributes' and it didn't use to leave blocky artefacts around the edges of the object. Something has changed or been broken or bugged in the last couple of updates.

Well, I can't reproduce that here, but HEVC is still a heavily compressed format.
I'd consider a better codec instead for delicate work with an alpha channel.

[quote="NoobNoob"]
Were you able to fix it?

I'm having the same problem. Both H265 and MP4/QuickTime have a strange black outline.

I can only export as alpha properly in CineForm or DNxHR. But these codecs are heavy and not very compatible compared to MP4/QuickTime.

Regarding the MP4, I was only able to activate alpha when importing by marking “Alphe mode premultiplied” in clip attributes.

I think Resolve should detect when an H265 MP4 has an alpha channel and activate it automatically, because if a person uses an alpha file, they certainly want to use it as alpha most of the time, so this should be the default behavior.

MP4 H265

Screenshot 2024-11-22 002019.png (48.88 KiB) Viewed 2704 times

QuickTime H265

Screenshot 2024-11-21 234116.png (16.85 KiB) Viewed 2704 times

DNxHR ou CineForm

Screenshot 2024-11-21 234152.png (78.24 KiB) Viewed 2704 times

Exporting alpha (transparent background) fails with H.265 but works with AppleProRes in Davinci Resolve 20.0, too.

The H.265 quicktime does not have the transparent background when it is imported to another project, whereas the prores quicktime does.

~Andrew~

Animation .mov - Quicktime H.265:

Alpha test - H.265

Bug 2025-05-30 Davinci Resolve 20.0 - No alpha for png in fusion from h.265 render.png (290.44 KiB) Viewed 657 times

Animation .mov - Quicktime ProRes:

Alpha test - ProRes

Bug 2025-05-30 Davinci Resolve 20.0 - No alpha for png in fusion from h.265 render - prores works.png (297.43 KiB) Viewed 657 times