Can you specify more than one output index in a transaction's input? It looks to me like each input to a bitcoin transaction has an index that specifies only one output from the input its spending. Is there a way to specify more than one output index, or do you have to create a second input line that contains the same input ID with a different index? It seems like that second way is wasteful of blockchain space - I would have thought there would be a way to simply specify multiple indexes. Is there a way to do that?
It looks to me like each input to a bitcoin transaction has an index that specifies only one output from the input its spending.


That is correct.


  Is there a way to specify more than one output index, or do you have to create a second input line that contains the same input ID with a different index?


You have to add an extra input, which repeats the txid.


  It seems like that second way is wasteful of blockchain space - I would have thought there would be a way to simply specify multiple indexes.


It is wasteful, but only slightly. In your hypothetical system, you still need a signature/scriptSig/witness for each of the coins being spent (unless you also want to incentivize key reuse), which are generally larger than a repetition of a txid.


  Is there a way to do that?


No.