First off, the different electronics shouldn't matter too much. Assuming we receive some sort of binary signal, then the format change is really not much different from converting, say, MP4 to AVI. Files are really just a bunch of numbers jumbled together in a way the computer can interpret.
Even binary probably isn't necessary. Number systems should be universal, and binary should therefore be the universally least complex system available and what they would likely use. It is entirely plausible, however, that they have some faster non-binary system that we cannot fathom. Even then, however, converting the data should still be trivial as it's a task computers do all the time.
We understand how their data is encoded. We need to know whether they use binary or some other number system. We need to know which pieces of data relate to which pixels. We need to know how they store audio files. In theory, we might be able to use algorithms make educated guesses as to how the format works, given a small/simple file type (OBJ files are pretty easy to guess), but that would be incredibly difficult. Much easier if they send along some handy instructions for which bits mean what.
Moreover, we are assuming that they use video the same way we do (sound and picture). It is entirely plausible they have something else entirely that we wouldn't be able to comprehend even if we could recreate it. Still, assuming that the finished format is comprehensible to humans, converting it shouldn't be a problem.
Transmitting video back to them should be as straightforward as sending them an MP4 and instructions on what the data means. Again though, assuming they have the same concept of video screens/sound/etc. Though sending them instructions on building those devices is also doable.