[FFmpeg-trac] #7965(ffmpeg:new): Support for HEVC with Alpha

[FFmpeg]

#7965: Support for HEVC with Alpha
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             Reporter:  leemartin  |                     Type:  enhancement
               Status:  new        |                 Priority:  normal
            Component:  ffmpeg     |                  Version:  unspecified
             Keywords:             |               Blocked By:
             Blocking:             |  Reproduced by developer:  0
Analyzed by developer:  0          |
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 At WWDC this year, Apple introduced support for HEVC with Alpha to both
 their app and browser platforms. You can find their talk on the subject
 here:

 https://developer.apple.com/videos/play/wwdc2019/506

 I'm an amateur at FFmpeg but I went down a rabbit hole today, trying to
 create a video in this new format using the latest version of FFmpeg. I
 took a rather simple approach of using ffprobe on one of their example
 video files (found in the resources on the link above) to get a profile
 and attempting to tune an ffmpeg encoding command to fit the same profile.

 While the following command does recreate the profile, it does not retain
 the transparency of the source prores .mov file.

 {{{
 % ffmpeg -i puppets_with_alpha_prores.mov -c:v libx265 -tag:v hvc1
 -pix_fmt yuv420p -colorspace bt709 -color_primaries bt709 -color_trc bt709
 puppets_with_alpha_hevc.mov
 }}}

 Apple is pretty clear about how they are achieving this encoding in their
 talk and examples. Naturally, I didn't follow anything they said and
 simply tried to hack a solution.

 So I'm wondering if this is something FFmpeg can do or would be able to
 support in the future?

 Thanks for the help!

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Ticket URL: <https://trac.ffmpeg.org/ticket/7965>
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