HEVC - Preserve alpha not working

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Level 1

4 points

HEVC - Preserve alpha not working

I just purchased Compressor for the sole reason that Media Encoder HEVC compression doesn't have the option to preserve alpha. After first solving the 'unable to submit to queue' issue, I finally have the export working. But, no matter what I do, the alpha channel doesn't carry through.

Tried different renders for the input file (prores 4444, uncompressed, etc), all with alpha channels (double checked after render). But to no avail. I have spend half a day now on what should be a 5 minute job and the frustration is pouring out of my ears. Please advice.

Settings in Compressor:

File output (alpha: none)

MacBook Pro 15″, macOS 12.2

Posted on Mar 8, 2022 3:12 AM

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Answer 1

Mar 8, 2022 5:04 AM in response to StudioGaar

Wait... there is something weird going on!

In my first test, I exported HEVC with alpha, at 8 bits. I imported the resulting file to FCP and it appeared to have a black background, no alpha (I have the viewer background set to checkerboard).

Then I thought... well, maybe it works if I choose 10 bits instead. So I did, and dragged the new file to FCP. It not just showed transparency, but now also the first file (the one exported as 8 bit) shows transparency as well!

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Answer 2

StudioGaar Author

Level 1

4 points

Mar 24, 2022 8:18 AM in response to Tom Wolsky

I know, same here. It's driving me nuts, but perhaps I'm missing something. Tried with both straight and premultiplied mattes. Also just tried to render from an uncompressed / lossless mov with alpha. Same issue occurs.

Ok, so update. The issue might not be the export. It might be importing it in AE or Premiere to check. Just found this:

"After Effects and Premiere does not recognize the alpha channel, so this codec really only works as a delivery codec"

I feel dumb now. But also amazed. Any tips on another way to check whether the export works?

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Answer 3

StudioGaar Author

Level 1

4 points

Mar 24, 2022 9:08 AM in response to Luis Sequeira1

Thanks for this tip. I double checked in iMovie and the alpha works. So it was After Effects and Premiere that just didn't read the alpha channel right. Which is completely amazing to me, as they usually read out every file type or codec - sometimes with an extra codec install needed, but still. So I was looking at the problem all wrong. Thanks to both of you for putting some time in this and helping me reach the solution!

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Answer 4

Mar 24, 2022 9:01 AM in response to StudioGaar

Yes, iMovie exists and it's free.

You can get it from the App Store. The current version is 10.3.1.

I just dragged the HEVC video exported from Compressor over a solid color background in iMovie and can check the transparency, as expected.

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Answer 5

Tom Wolsky

Level 10

152,780 points

Mar 23, 2022 9:51 AM in response to StudioGaar

Luis could not reproduce the problem with QuickTime HEVC 8-bit. It works correctly for me as well. Perhaps your OS needs to be updated as it wasn't working earlier in the month. I'm using 12.3.

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Answer 6

Mar 8, 2022 4:58 AM in response to StudioGaar

I just tried a quick test: created a new setting, Quicktime Movie, HEVC, and checked "preserve alpha".

Exported a 4444 movie with alpha channel and got no alpha channel on the export, just as you are experiencing.

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Answer 7

Tom Wolsky

Level 10

152,780 points

Mar 23, 2022 7:49 AM in response to StudioGaar

No, this is a strictly user to user forum. Compressor engineering are probably aware of it, though using feedback is always useful. One more voice.

Oddly you can make a ProRes 4444 file with alpha into HEVC with transparency in the Finder, though the options are limited.

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Answer 8

Mar 23, 2022 9:15 AM in response to Tom Wolsky

Tom, were you able to reproduce this problem in Compressor?

I have been doing several experiments, taking a ProRes 4444 with Alpha Channel, and exporting to HEVC using 8-bit or 10-bit, faster encoding, slower encoding, and they are all coming out with the Alpha Channel correctly...

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Answer 9

StudioGaar Author

Level 1

4 points

Mar 24, 2022 2:57 AM in response to Tom Wolsky

Well, initially he was experiencing the same problem when trying to reproduce my issue:

"I just tried a quick test: created a new setting, Quicktime Movie, HEVC, and checked "preserve alpha".

Exported a 4444 movie with alpha channel and got no alpha channel on the export, just as you are experiencing."

Anyhow. I'm running 12.2.1. Which was a fresh update to Monterrey at the time (because it was necessary to install the latest Compressor in the first place). So let me try to update to 12.3 and see where that takes us.

Thanks!

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Answer 10

Mar 24, 2022 8:53 AM in response to StudioGaar

You can easily import into FCP or iMovie to check. In FCP, change the background to checkerboard to make it obvious which parts of the image are transparent. In iMovie, you could place the video atop some background image and check which parts of the image show through.

Note: it should be obvious in Quicktime Player or in Quicklook in the Finder, if they worked just like Preview does for still images; but alas those don't work, as they show transparent parts as black.

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Answer 11

Mar 23, 2022 9:19 AM in response to Tom Wolsky

Actually, I have to correct something I said. It is not producing 10-bit files with Alpha Channel. The moment I check "preserve alpha" it switches to 8-bit.

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Answer 12

StudioGaar Author

Level 1

4 points

Mar 23, 2022 4:42 AM in response to StudioGaar

Are there any Apple employees that roam this forum? Is this an issue that the development team is aware of? I'm stuck in a corner here, my client needs a HEVC file with alpha, the only application that can provide this is Compressor, which I bough specifically for this purpose - and it doesn't deliver what it's supposed to. Please advice.

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Answer 13

StudioGaar Author

Level 1

4 points

Mar 23, 2022 9:45 AM in response to Tom Wolsky

Thanks Tom, for the info and for giving this a go.

"Oddly you can make a ProRes 4444 file with alpha into HEVC with transparency in the Finder, though the options are limited."

Yes, indeed. Unfortunately, this doesn't give enough options for compression, leading to way to big a file size for the intended purpose. Also, strange stuff part two, this method also does not lead to a file with transparency.

I would say there is perhaps something wrong in my system. However, the fact that Luis can reproduce the problem leads me to think otherwise.

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Answer 14

StudioGaar Author

Level 1

4 points

Mar 23, 2022 9:47 AM in response to Luis Sequeira1

Did you ever find a fix? Because in your earlier reply, they also came out wrong for you.

Importing FCP is not an option for me, as I do not work with FCP and am not inclined to purchase another program just to fix this bug.

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Answer 15

Tom Wolsky

Level 10

152,780 points

Mar 24, 2022 5:58 AM in response to StudioGaar

I can’t see why it wouldn’t work. It cannot be machine specific. I’m assuming the original has a correct alpha channel. Perhaps you could share the primal file to test. Maybe using WeTransfer ot Dropbox.

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HEVC - Preserve alpha not working

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