Function channel_layout_description_from_ffmpeg 

pub fn channel_layout_description_from_ffmpeg(
    value: &ChannelLayout,
) -> ChannelLayoutDescription

Builds a fully-populated ChannelLayoutDescription from an FFmpeg AvChannelLayout.

• Native / Ambisonic layouts populate native_mask from AvChannelLayout::bits (clearing it to None if zero).
• Custom layouts populate custom_channels from FFmpeg’s per-channel list (AVChannelLayout.u.map), with each label drawn from AVChannelCustom.name.
• text carries the result of av_channel_layout_describe (FFmpeg’s human-readable rendering — e.g. "5.1(side)").
• known_kind runs channel_layout_from_ffmpeg’s two rungs against that same single rendering: constant table first, then the describe rung.