incorrect help msg for -h decoder=ayuv

[Glenn Slayden]

Summary of the bug:
How to reproduce:

% ffmpeg -h decoder=ayuv
ffmpeg 4.1
built on 20181017

Result of the command:

V....D ayuv Uncompressed packed MS 4:4:4:4

According to the following website the planar format should be referred to as "4:4:4":

​https://docs.microsoft.com/en-us/windows/win32/medfound/recommended-8-bit-yuv-formats-for-video-rendering#ayuv

Note that ffmpeg lists an extra ":4" in the help text for the decoder name.

[Balling]

This looks right, see ​https://github.com/FFmpeg/FFmpeg/commit/2ed8baa614839bffa2df0fb14687239994613892

It is 4:4:4(:4). But I am not a guru in this))

[Carl Eugen Hoyos]

The linked MS documentation clearly describes a 4:4:4:4 format.

[Glenn Slayden]

Ok, thanks. I guess its an error on the MS site then, that it says:

4:4:4 Formats, 32 Bits per Pixel

AYUV
A single 4:4:4 format is recommended, with the FOURCC code AYUV.