This answer was inspired by Mokubai's comments (feel free to edit if it misses the mark).
Neither of the other answers really focuses on the critical criteria.
Whether or not a question is on-topic isn't governed by the potential answer; the question needs to be judged on its own merits. For example, a question can't request a software recommendation, but software can be recommended as a solution.
If, in the example here, the OP was trying to go directly from a phone to a DVD player, that whole process would be off-topic. An answer could be to inject a computer into the process to solve it, but as covered above, the potential answer doesn't affect whether the question is on-topic.
We might anticipate that the problem can be fixed only by doing something to the DVD player. We don't know that for sure, and closure on that basis would preclude getting an answer with a computer-based solution.
Potential answers (or comments) could be:
I think the only solution is modifying the DVD player, and we can't help with that because it is out-of-scope.
Based on yakkity-blah authoritative source, the only solution would be to modify the DVD player in a fundamental way, which cannot be done, so sorry, there's no solution to the problem.
But such answers are acceptable, and don't make the question off-topic.
Absence of a computer would disqualify the question, but the presence of a computer doesn't guarantee that the question is on-topic. The fact that a computer is involved in the OP's process means that it isn't off-topic as not involving a computer, but that, alone, isn't enough to make it on-topic; that only gets it consideration. Other context in the question determines whether it's on-topic.
The DVD player doesn't make it off-topic. Even though that's where the symptom appeared, and even if the computer didn't actually contribute to the symptom, that, alone, doesn't make the question off-topic.
What does it depend on?
The OP's process, hardware, and symptoms are just the history that brought us to the question. What drives whether or not the question is on-topic is the question -- what is the OP asking us to help them do?
- If the question is this, it is off-topic:
Having described the history, I know that the problem is with the DVD Player. How do I fix the DVD player so it will properly play the videos?
- If the question is this, it is on-topic:
What can I do on the computer to diagnose the issue and/or produce DVDs that will play properly on the DVD player?
In this question, the OP wasn't specific. They just wanted the problem solved. So how do we determine whether or not it's on-topic? We can approach it like this:
Speaking generally, the question would be on-topic if the OP was looking for a computer-based solution, and the OP didn't request an off-topic solution; they just want a solution. We can help with one but not the other, so why not pursue the path we can help on?
But specific to the particulars of this question, the OP's stated goal wasn't to play videos on the DVD player, it was to share the videos with others. Using DVDs was just one way to share large files. The DVD player happened to be a test bed to verify that the DVDs worked. The symptom raised the question of whether the DVDs might also mess up on other equipment that might be used to view them.
The problem wasn't necessarily limited to the DVD player, so a solution of fixing the player wouldn't even solve the problem. That being the case, the fact that it would be off-topic isn't a relevant criterion. A solution might actually be just to tell the friends to view the videos on their computer rather than other equipment. Problem solved with a zero tech solution.
The question can be edited to better focus it as on-topic. Rather than just leave it up in the air and subject to interpretation, add a request for an on-topic solution.
How can I diagnose the file incompatibility issue, and is there a way to modify the file on the computer to make it compatible with a DVD player?
Perhaps the biggest take-away from the question is not so much the answer of why it is or isn't on-topic, but why it led to opposite viewpoints. The question didn't actually ask a question or request a specific action or result. It just stated an unexpected history. Readers extrapolated and filled in the blank for themselves after picking up on different aspects of what was reported. What we each saw was completely consistent with the facts as we read them, so our positions seemed obvious and correct, and we never noticed that the question was missing a question.