函数 av_muxer_iterate 

pub unsafe extern "C" fn av_muxer_iterate(
    opaque: *mut *mut c_void,
) -> *const AVOutputFormat

Iterate over all registered muxers.

@param opaque a pointer where libavformat will store the iteration state. Must point to NULL to start the iteration.

@return the next registered muxer or NULL when the iteration is finished