pe(OSSL_ENCODER_CTX *ctx,
                                      const char *output_type);
 int OSSL_ENCODER_CTX_set_output_structure(OSSL_ENCODER_CTX *ctx,
                                           const char *output_structure);

 int OSSL_ENCODER_CTX_add_encoder(OSSL_ENCODER_CTX *ctx, OSSL_ENCODER *encoder);
 int OSSL_ENCODER_CTX_add_extra(OSSL_ENCODER_CTX *ctx,
                                OSSL_LIB_CTX *libctx, const char *propq);
 int OSSL_ENCODER_CTX_get_num_encoders(OSSL_ENCODER_CTX *ctx);

 typede