函数 avformat_index_get_entry 

pub unsafe extern "C" fn avformat_index_get_entry(
    st: *mut AVStream,
    idx: c_int,
) -> *const AVIndexEntry

Get the AVIndexEntry corresponding to the given index.

@param st Stream containing the requested AVIndexEntry. @param idx The desired index. @return A pointer to the requested AVIndexEntry if it exists, NULL otherwise.

@note The pointer returned by this function is only guaranteed to be valid until any function that takes the stream or the parent AVFormatContext as input argument is called.