[FFmpeg-trac] #5792(undetermined:closed): Alpha planes not found/ignored decoding VP8a/VP9a (VPxa)

[FFmpeg]

#5792: Alpha planes not found/ignored decoding VP8a/VP9a (VPxa)
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             Reporter:  cdlvcdlv     |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:  invalid
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by cdlvcdlv):

 So that's the option I needed. Thank you.

 This way it's possible to use {{{overlay}}} in **ffmpeg** to blend two
 videos or use {{{alphaextract}}} in **ffplay**, but I cannot make a proper
 {{{overlay}}} in **ffplay** because it accepts only one input. Then I must
 use {{{movie}}} filter, but I cannot specify the {{{-vcodec libvpx}}}.

 As I said, I googled for an additional option to make the new decoder work
 but I didn't find it. Where was this documented? That's why I thought
 there was a problem and opened the ticket. Sorry.

 I'll try the {{{--disable-decoder=vp8,vp9}}} but I think that, when VPxa
 is used as input or in a filter, {{{libvpx}}} should be understood. Why
 would anyone want to overlay a video with alpha (no matter the codec) on a
 background ignoring the alpha planes? At least it's the improbable case.

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Ticket URL: <https://trac.ffmpeg.org/ticket/5792#comment:2>
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