Function video_encoder_capabilities 

pub fn video_encoder_capabilities(
    codec: NativeVideoCodec,
) -> Vec<NativeVideoEncoderCapability>

The encoders usable for codec alone, as codec_capabilities lists them.

An export needs only its own codec’s, and an encoder whose registration does not prove it runs here is opened to find out ([encoder_runs_here]): asking for one codec opens only that codec’s.