Opened 12 days ago

Last modified 7 days ago

#6718 new enhancement

Option to remove label on alpha channel

Reported by: ttdww Owned by:
Priority: wish Component: undetermined
Version: unspecified Keywords: alpha
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

Summary of the bug:

When FFMPEG writes to RGBA PNG 32bit .MOV Quicktime, it seems to label alpha to be interpreted as 'straight' when we need the files to have 'no label' so After effects can remember it's own interpretation setting for 'Import of an unlabeled alpha'. Otherwise users will constantly have to force the interpretation of every FFMPEG created PNG file they import regardless of what After Effects is set to.

Version of FFMPEG: ffmpeg-20170921-183fd30-win64-static

How to reproduce:
ffmpeg.exe -r 24 -f image2 "explosion.%%04d.exr" -vcodec png -pix_fmt rgba -y "explosion.mov"

If we are doing something wrong, we apologize. We have searched far and wide for an answer.

Change History (8)

comment:1 Changed 12 days ago by cehoyos

  • Keywords label interpret removed
  • Priority changed from important to wish
  • Type changed from task to enhancement

comment:2 Changed 12 days ago by ttdww

Hi Cehoyos,

Since I see this was changed from bug to wish, I'm guessing there is no way to control this currently?

From other programs we've used here, 3ds max, After Effects, etc., the alpha channel of most QT files outputted is always 'unlabeled', so we're hoping this can be added to FFMPEG soon. For now, we're going to have to keep command-line AE in our workflow to process files.

Thanks again for your time.

comment:3 Changed 12 days ago by ttdww

I'm seeing something in the docs about -vf unpremultiply (http://ffmpeg.org/ffmpeg-filters.html#toc-unpremultiply) though I'm not clear on how to use it with switches.

Perhaps an example would help us. Thanks!

comment:4 Changed 12 days ago by ttdww

Ok, that only affects the input. The output file still have alpha labeled as 'straight'.

comment:5 Changed 12 days ago by cehoyos

Will the change affect the png encoder or the mov muxer?

comment:6 Changed 12 days ago by ttdww

I'm thinking the mov muxer overall? Or even beyond that, it could affect any filetype that supports outputted alpha (Quicktime PNG, QT Animation, EXR, TGA..). However the primary issue for us, currently, is to have it work with PNG RGBA.

[Edit] I realize now I may have misunderstood your question. If you are asking me if it will affect either one of those or both, I'm not sure.

Last edited 12 days ago by ttdww (previous) (diff)

comment:7 Changed 12 days ago by ttdww

From what I'm understanding, some filetypes (not sure which ones, but definitely Quicktime PNG 32bit) can get a property or metadata string added to the file which defines how the alpha should be interpreted. Most programs I've seen that output PNG don't add one so that the image editing app importing it can force it to it's own setting per that app. Somehow when FFMPEG is writing it, it seems it's getting that property added and set to 'straight'. This is my best guess, however I'm not a coder.

Last edited 12 days ago by ttdww (previous) (diff)

comment:8 Changed 7 days ago by ttdww

Hi,

Was that a question for me?

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