Allow using additional pixel formats with libvpx-vp9

[GreatEmerald]

Currently ffmpeg assumes that libvpx is only capable of yuv420p pixel format. However, libvpx-vp9 with Profile 1 allows additional pixel formats - yuv422p and yuv444p, and possibly also yuva422p and yuva444p (the libvpx code states that they also support alpha in Profile 1). So these pixel formats should be made available.

The code comments for that can be found here (line 1133):
​https://chromium.googlesource.com/webm/libvpx/+/2344e3a2e1600a2a31e63d2a82a9bbd0b91912b0/vp9/encoder/vp9_bitstream.c
The announcement of yuv444p support can be found here:
​https://groups.google.com/a/webmproject.org/forum/?fromgroups=#!topic/webm-discuss/UzoX7owhwB0

[GreatEmerald]

Still happens in libavcodec 55.52.102.

[SocDemScum]

libavcodec 56.19.100 produces an error saying that yuv420p colour spaces can only be used on profile 0 and 2, when telling it to use profile 1 and a yuv444p colour space.

[cehoyos]

Is this still a valid ticket for yuva4xxp or was alpha abandoned for vp9?

[jzern]

Alpha never made it to the final vp9 bitstream, but can be done in the same way as vp8 -- encoding and muxing the alpha plane separately.

[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");

[cehoyos]

Implemented by Vignesh Venkatasubramanian in acca56d9629b7fc158ce188190d22314c3d92c39