RGBA movie rendering: WebM/VP9 codec missing alpha channel #80769

New Issue

Georg K · 2020-09-14T13:35:32+02:00

Georg K commented

2020-09-14 13:35:32 +02:00

System Information
Operating system: Linux-5.8.6-1-MANJARO-x86_64-with-glibc2.32 64 Bits
Graphics card: AMD VERDE (DRM 2.50.0, 5.8.6-1-MANJARO, LLVM 10.0.1) X.Org 4.5 (Core Profile) Mesa 20.1.7

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-14 10:24, hash: b8a25bbd8a, also broken in 2.82a
Worked: (newest version of Blender that worked as expected)

Short description of error
Rendering a movie with alpha channel works for

ffmpeg video codec #1
png codec
HuffYUV codec
But choosing WebM/VP9 does not include an alpha channel, so either the RGBA option should not be there or something is wrong in the encoding step.

Edit
Exported movie looks like it has proper alpha, but Blender (next to other software cannot import that properly)

Exact steps for others to reproduce the error
In the default scene:
render properties: Film transparent
output properties: File Format: FFmpeg video, Color RGBA, Video Codec: WebM/VP9
Render Animation and open the file: black background is still there, no checkerboard like with the working codecs, also putting it over a solid color in the sequencer using Alpha Over clearly shows that there is no alpha channel.

**System Information** Operating system: Linux-5.8.6-1-MANJARO-x86_64-with-glibc2.32 64 Bits Graphics card: AMD VERDE (DRM 2.50.0, 5.8.6-1-MANJARO, LLVM 10.0.1) X.Org 4.5 (Core Profile) Mesa 20.1.7 **Blender Version** Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-14 10:24, hash: `b8a25bbd8a`, also broken in 2.82a Worked: (newest version of Blender that worked as expected) **Short description of error** Rendering a movie with alpha channel works for - ffmpeg video codec #1 - png codec - HuffYUV codec But choosing WebM/VP9 does not include an alpha channel, so either the RGBA option should not be there or something is wrong in the encoding step. **Edit** Exported movie looks like it has proper alpha, but Blender (next to other software cannot import that properly) **Exact steps for others to reproduce the error** In the default scene: render properties: Film transparent output properties: File Format: FFmpeg video, Color RGBA, Video Codec: WebM/VP9 Render Animation and open the file: black background is still there, no checkerboard like with the working codecs, also putting it over a solid color in the sequencer using Alpha Over clearly shows that there is no alpha channel.

Georg K commented

2020-09-14 13:35:32 +02:00

Added subscriber: @georgK

blender-admin commented

2020-09-14 13:35:32 +02:00

#85430 was marked as duplicate of this issue

Philipp Oeser commented

2020-09-14 14:28:05 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-09-14 14:28:05 +02:00

But choosing WebM/VP9 does not include an alpha channel, so either the RGBA option should not be there or something is wrong in the encoding step.

Should be supported, see 43b7512a59

I cannot get it to show either, but it might be me using it wrong.

> But choosing WebM/VP9 does not include an alpha channel, so either the RGBA option should not be there or something is wrong in the encoding step. Should be supported, see 43b7512a59 I cannot get it to show either, but it might be me using it wrong.

Philipp Oeser commented

2020-09-14 14:56:21 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Philipp Oeser commented

2020-09-14 14:56:21 +02:00

Added subscriber: @dr.sybren

Philipp Oeser commented

2020-09-14 14:56:21 +02:00

Here is a file I created with following settings (and transparent film)

0001-0100.webm

This actually looks like it holds transparency (in the browser)?
(cannot get it to show in Blender though)

@dr.sybren : is it possible we are not importing it correctly?

Here is a file I created with following settings (and transparent film) ![image.png](https://archive.blender.org/developer/F8878464/image.png) [0001-0100.webm](https://archive.blender.org/developer/F8878466/0001-0100.webm) This actually looks like it holds transparency (in the browser)? (cannot get it to show in Blender though) @dr.sybren : is it possible we are not importing it correctly?

Georg K commented

2020-09-14 15:21:01 +02:00

You are right, it works in kdenlive, too. But VLC, mpv and Blender don't recognize the alpha channel in the VP9.

Georg K commented

2020-09-20 13:57:25 +02:00

This comment was removed by @georgK

*This comment was removed by @georgK*

Richard Antalik commented

2020-09-28 09:20:19 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-09-28 09:20:19 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Archived'

Richard Antalik closed this issue

2020-09-28 09:20:19 +02:00

Richard Antalik self-assigned this 2020-09-28 09:20:19 +02:00

Richard Antalik commented

2020-09-28 09:20:19 +02:00

In #80769#1015268, @georgK wrote:
You are right, it works in kdenlive, too. But VLC, mpv and Blender don't recognize the alpha channel in the VP9.

I have looked into this, and image was rendered fully opaque by ffmpeg itself. After some googling, I have found https://trac.ffmpeg.org/ticket/8344
Comment states that "The native VP8/9 decoders don't decode alpha". So this isn't supported at the moment.

Since encoding works correctly, I will close this report.

> In #80769#1015268, @georgK wrote: > You are right, it works in kdenlive, too. But VLC, mpv and Blender don't recognize the alpha channel in the VP9. I have looked into this, and image was rendered fully opaque by ffmpeg itself. After some googling, I have found https://trac.ffmpeg.org/ticket/8344 Comment states that "The native VP8/9 decoders don't decode alpha". So this isn't supported at the moment. Since encoding works correctly, I will close this report.

Georg K commented

2020-09-28 20:35:38 +02:00

Thanks for finding the source of the problem.
While it's not Blender's fault, shouldn't users be warned that this format is an exception and that the alpha channel will be lost if the video will be used in Blender?
I tried adding it here https://docs.blender.org/manual/en/dev/files/media/video_formats.html, but this page can't be edited by me (a warning in the UI would be more effective of course).

Thanks for finding the source of the problem. While it's not Blender's fault, shouldn't users be warned that this format is an exception and that the alpha channel will be lost if the video will be used in Blender? I tried adding it here https://docs.blender.org/manual/en/dev/files/media/video_formats.html, but this page can't be edited by me (a warning in the UI would be more effective of course).

Richard Antalik was unassigned by Sybren A. Stüvel

2020-09-29 17:43:17 +02:00

Sybren A. Stüvel self-assigned this 2020-09-29 17:43:17 +02:00

Sybren A. Stüvel commented

2020-09-29 17:43:17 +02:00

Changed status from 'Archived' to: 'Resolved'

Sybren A. Stüvel commented

2020-09-29 17:43:17 +02:00

In #80769#1024974, @georgK wrote:
While it's not Blender's fault, shouldn't users be warned that this format is an exception and that the alpha channel will be lost if the video will be used in Blender?

Yes, so I did.

> In #80769#1024974, @georgK wrote: > While it's not Blender's fault, shouldn't users be warned that this format is an exception and that the alpha channel will be lost if the video will be used in Blender? Yes, so I did.

Georg K commented

2020-09-30 00:22:03 +02:00

Thank you!

Evan Wilson commented

2021-02-07 08:57:12 +01:00

Added subscriber: @qubodup

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RGBA movie rendering: WebM/VP9 codec missing alpha channel #80769