函数 avcodec_parameters_from_context 

pub unsafe extern "C" fn avcodec_parameters_from_context(
    par: *mut AVCodecParameters,
    codec: *const AVCodecContext,
) -> c_int

Fill the parameters struct based on the values from the supplied codec context. Any allocated fields in par are freed and replaced with duplicates of the corresponding fields in codec.

@return >= 0 on success, a negative AVERROR code on failure