[FFmpeg-trac] #3271(avcodec:open): Allow using additional pixel formats with libvpx-vp9

[FFmpeg]

#3271: Allow using additional pixel formats with libvpx-vp9
--------------------------------------+-----------------------------------
             Reporter:  GreatEmerald  |                    Owner:
                 Type:  enhancement   |                   Status:  open
             Priority:  wish          |                Component:  avcodec
              Version:  git-master    |               Resolution:
             Keywords:  libvpx        |               Blocked By:
             Blocking:                |  Reproduced by developer:  0
Analyzed by developer:  0             |
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Comment (by cdlvcdlv):

 I've made vp8/webm videos with alpha using ffmpeg with this command:

 {{{
 ffmpeg -i INPUT -c:v libvpx -pix_fmt yuva420p -metadata:s:v:0
 alpha_mode="1" OUTPUT.webm
 }}}

 But when I try

 {{{
 ffmpeg -i INPUT -c:v libvpx-vp9 -pix_fmt yuva420p -metadata:s:v:0
 alpha_mode="1" OUTPUT.webm
 }}}

 ffmpeg complains and changes the pixel format

 {{{
 Incompatible pixel format 'yuva420p' for codec 'libvpx-vp9', auto-
 selecting form at 'yuv420p'
 }}}

 Nevertheless, it seems there is a little utility to make vp9 videos. I've
 not tested it to see whether it works using Chrome but, as a part of
 chromium, we could assume compatibility.

 {{{
 https://chromium.googlesource.com/webm/webm-tools/+/master/alpha_encoder/
 }}}

 The README tells about VP8 only, but in the source code you can see the
 options:

 {{{
 printf(" -c codec (vp8 or vp9). default is vp8\n");
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/3271#comment:6>
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